Journal of Colloid And Interface Science (v.360, #2)
Developing a self-assembled monolayer microarray to study stem cell differentiation
by Wei Luo; Muhammad N. Yousaf (pp. 325-330).
We have integrated microarray technology with SAMs on gold to develop a well-defined model substrate for high-throughput investigation of cell-surface interactions. This system is able to control the composition, ligand density, and spatial distribution of SAMs on the surface to probe the chemical effects on stem cell differentiation.Display Omitted► A self-assembled monolayer (SAM) microarray chip was generated. ► Electrochemistry analysis provides precise surface chemistry composition of the chip. ► SAM arrays are applied to the study of stem cell differentiation.We have developed a novel strategy to generate self-assembled monolayer microarray (SAMs-Array) of alkanethiolates on gold surfaces for the study of human mesenchymal stem cells (hMSCs) differentiation. Electroactive alkanethiols were microarray-printed in varying densities to probe the chemical effects on stem cell differentiation. Cyclic voltammetry (CV) was used for the precise determination of the amount of alkanethiol molecules transferred and SAMs formed on the microarray. We can also control the oxidative and reductive state of each molecule displayed to cells by CV. Based on this SAMs-Array technology, we generated a platform for potential high-throughput screening of various surface chemistry effects on cell behaviors for future applications in biomaterials and tissue engineering.
Keywords: Microarray; Electroactive; Self-assembled monolayers; SAMs-Array; Stem cell
Thickness measurement of colloidal opal crystal growth by Bragg reflection
by Ming-Zheng Lin; Guan-Hui Li; Ming-Yau Chern; Chung-Wen Lan (pp. 331-334).
The left side is the results of reflectance spectrum from measurement and simulation, the right side is the SEM observation, they are in good agreement in thickness of opal crystals.Display Omitted► The reflectance simulation estimates the thickness of the opal crystals. ► The reflectance simulation results are in good agreement with SEM observation. ► Different velocity of substrates will make different thickness of the opal crystals.This study investigates a simple method for thickness estimation with single layer accuracy for self-assembling opal crystals prepared by the dip-coating method. The thickness (number of layers) of the opal crystals was estimated by an analysis of the optical reflectance from s-polarization incident light, and then verified with SEM. The opal crystals were considered as periodic dielectric layers and were analyzed with the transfer matrix method. The reflectance simulation showed a good agreement with the experimental results. The lattice constant and the thickness were determined at the peak position and by the fringes of the reflection spectra, respectively.
Keywords: Opal crystal; Dip-coating; Bragg reflection and transfer matrix
Enzymatic tailoring for precise control of plasmonic resonance absorbance of gold nanoparticle assemblies
by Joong Hyun Kim; Jung-Won Kim; Bong Hyun Chung (pp. 335-340).
We could obtain precise control of plasmonic property of AuNP assemblies on hyaluronic acid by tailoring the size of the templates with hyaluronicdases.Display Omitted► Gold nanoparticles are assembled on HAs. ► Tailoring of the size of HA with HAases allows precise control of the palsmonic absorbance of the array. ► Nearly one dimensional array of AuNPs is also obtained.We report an enzymatic method to control the plasmon resonance absorbance of gold nanoparticle (AuNP) arrays assembled on hyaluronic acids. While multiple electrostatic interactions between cysteamine on the AuNPs and the carboxylic acid residues in the whole intact hyaluronic acid induced the formation of large aggregates, precise control of the plasmon absorbance was possible by tailoring the size of the bio-polymeric templates with hyaluronidase, almost over the entire range of the resonant coupling wavelengths. It was possible to precisely tune the position of the second plasmon absorbance by manipulating the amount of the template and the enzymatic hydrolysis time. Finally, we were able to produce a chain-like array of AuNPs, which was nearly one dimensional, with a maximum shift of up to 189nm in the plasmon absorbance at the optimal hydrolysis time of the templates. This enzymatic method can be used as a useful tool to tailor the plasmonic properties of the nanostructures required for specific applications.
Keywords: Gold nanoparticles; Surface plasmonic resonance; One dimensional array; Hyalurnoic acid; Hyaluronidase
Synthesis of citrate-stabilized hydrocolloids of hydroxyapatite through a novel two-stage method: A possible aggregates–breakdown mechanism of colloid formation
by Cuicui Li; Liping Zhao; Jingjia Han; Ruifang Wang; Chengdong Xiong; Xingyi Xie (pp. 341-349).
The ligand–particle chelation induced the HA particles to loosely aggregate during low-temperature reaction (a). High-temperature aging broke some ligand–particle links, forming colloidal particles stabilized by their surface charge (b).Display Omitted► Citrate-stabilized hydroxyapatite (HA) hydrocolloids were synthesized through a novel two-stage method. ► The HA hydrocolloid remains stable for over 2years. ► The conformational changes in citrate ions on HA at different temperatures explain the colloid formation process.Long-term stable (>2years) hydrocolloids of hydroxyapatite (HA) were synthesized via a low-temperature (18–50°C) reaction of aqueous ammonium phosphate with calcium nitrate in the presence of citrate ions, followed by an aging process at high temperature (80–99°C) for 4h. Changing the reaction and/or aging temperature seldom yielded stable HA hydrocolloids. The as-prepared hydrocolloids were desalinated through ultrafiltration where their average particle size gradually decreased, bottomed out at 100–400μS/cm, and sharply increased in parallel with a decrease in solution conductivity. The colloid formation is most likely through a temperature-sensitive aggregates–breakdown process. During low-temperature reaction, citrate–calcium chelation bridges the growing HA particles into loose aggregates. High-temperature aging disrupts these inter-particle links and thus breaks the aggregates, imparting negative charges to the HA, forming colloidal particles stabilized by surface charge. The decrease in mean particle size during early ultrafiltration suggested that the aggregate breakdown further proceeded through desalination. In conclusion, the temperature-dependent interactions between citrate ions and calcium sites on HA particles played key roles in the synthesis and stability of the HA colloids.
Keywords: Hydroxyapatite; Hydrocolloid; Long-term stability; Citrate; Aggregates–breakdown; Ultrafiltration
Facile fabrication of amphiphilic gold nanoparticles with V-shaped brushes from block copolymers with a trithiocarbonate group as the junction
by Zhao-Li Wang; Jun-Ting Xu; Bin-Yang Du; Zhi-Qiang Fan (pp. 350-354).
Amphiphilic AuNPs with V-shaped brushes were prepared by grafting a PS- b-PEO block copolymer with a trithiocarbonate group as the junction to the Au surface..Display Omitted► A PS- b-PEO block copolymer with a trithiocarbonate group as the junction was prepared. ► AuNPs with V-shaped brushes (Au-V-brushes) were prepared by anchoring the trithiocarbonate group to the Au surface. ► The obtained Au-V-brushes are soluble in both water and organic solvent. ► The Au-V-brushes can transfer from the water into toluene or from toluene to the interface.Amphiphilic gold nanoparticles grafted with V-shaped brushes (Au-V-brushes) were prepared by grafting a polystyrene- b-poly(ethylene oxide) (PS- b-PEO) block copolymer with a trithiocarbonate group as the junction to the Au surface. The obtained Au-V-brushes were subjected to solubility test and UV–vis, FT-IR, TEM and DLS characterizations. It is found that the Au-V-brushes are soluble in both water and organic solvents. In the common solvent DMF, the size of the Au-V-brushes is about 17nm, whereas in selective solvents (toluene and water) aggregates of 70–90nm are formed. Phase transfer of the Au-V-brushes from the water phase into the toluene phase occurs upon addition of Na2SO4 into water and the Au-V-brushes can also transfer from the toluene phase to the interface of toluene and water phases after addition of citric acid in the water phase.
Keywords: Gold nanoparticles; Mixed brushes; Block copolymer; Trithiocarbonate
Moderating effect of ammonia on particle growth and stability of quasi-monodisperse silver nanoparticles synthesized by the Turkevich method
by Luiz F. Gorup; Elson Longo; Edson R. Leite; Emerson R. Camargo (pp. 355-358).
The formation of diamine silver complex prevents the reduction of silver ion..Display Omitted► Stable silver nanoparticles of 2nm were obtained using ammonia to control the particle growth mechanism. ► Stable silver nanoparticles with sizes as small as 1.6nm were obtained after 17min of reaction. ► Soluble diamine silver (I) complexes played an important role in the nanoparticles stabilization. ► Morphology and particle size at ambient temperature do not change in the course of several months.A new method to stabilize silver nanoparticles by the addition of ammonia is proposed. Colloidal dispersions of silver nanoparticles were synthesized by the Turkevich method using sodium citrate to reduce silver nitrate at high pH and at 90°C. After approximately 12min, a diluted ammonia solution was added to the reaction flask to form soluble diamine silver (I) complexes that played an important growth moderating role, making it possible to stabilize metallic silver nanoparticles with sizes as small as 1.6nm after 17min of reaction. Colloidal dispersions were characterized by UV-visible absorption spectroscopy, X-ray diffraction, and transmission electronic microscopy.
Keywords: Silver nanoparticles; Turkevich method; Growth and stability
Interaction of naproxen amphiphilic derivatives with biomembrane models evaluated by differential scanning calorimetry and Langmuir–Blodgett studies
by Dorotea Micieli; Maria Chiara Giuffrida; Rosario Pignatello; Francesco Castelli; Maria Grazia Sarpietro (pp. 359-369).
Structures of naproxen (NAP), NAP-EDA-LAA10 and NAP-EDA-LAA 14.Display Omitted► NAP–EDA–LAA10 and NAP–EDA–LAA14 prodrugs were obtained by conjugation of naproxen with lipoaminoacids through a diethylamine spacer. ► The interaction of NAP and prodrugs with biomembrane models was studied by differential scanning calorimetry and Langmuir–Blodgett techniques. ► The prodrugs showed a stronger interaction than naproxen with the biomembrane models.Anti-inflammatory drugs represent a potential new strategy for the treatment of Alzheimer’s disease (AD). The ability to cross the blood–brain barrier and to reach brain tissues is a critical point for these drugs and is strictly related to their lipophilicity.Naproxen (NAP) is a non-steroidal anti-inflammatory drug (NSAIDs) under active investigation for AD. To improve its lipophilic character, NAP was conjugated through a diethylamine spacer (EDA) to lipoamino acids (LAA), α-amino acids containing a long alkyl side chain, to obtain the NAP–EDA–LAA10 and NAP–EDA–LAA14 prodrugs.The interaction of NAP and prodrugs with dimyristoylphosphatidylcholine phospholipids, forming either multilamellar vesicles or monolayers (at the air/water interface) and used as biomembrane models, was studied by differential scanning calorimetry and Langmuir–Blodgett techniques.Experimental data showed that NAP conjugation with LAA residues was able to enhance the drug interaction with such biomembrane models.
Keywords: Naproxen; Lipoamino acids; Alzheimer’s disease; DSC; LB; Amphiphilicity
Poly(zinc dimethacrylate) as a precursor in the low-temperature formation of ZnO nanoparticles
by Gabriela Ambrožič; Srečo D. Škapin; Majda Žigon; Zorica Crnjak Orel (pp. 370-376).
A low-temperature synthesis of pure ZnO nanoparticles and polymer–ZnO hybrid materials formed by the NaOH-mediated conversion of poly(zinc dimethacrylate) in 1-butanol is presented.Display Omitted► A novel synthesis of pure ZnO nanoparticles and polymer–ZnO hybrid materials is reported. ► The conversion of poly(zinc dimethacrylate) in 1-butanol proceeds by the addition of the NaOH. ► The polymer was used as a precursor and template in the low temperature preparation of neat ZnO.We present a simple, low-temperature synthesis of pure ZnO nanoparticles and polymer–ZnO hybrid materials formed by the NaOH-mediated conversion of poly(zinc dimethacrylate) in 1-butanol. The polymer poly(zinc dimethacrylate) was used as a precursor to prepare neat ZnO particles. It has a double role in the ZnO formation process, acting as a template and simultaneously controlling the crystal growth. The obtained single-crystalline ZnO nanorods show a low tendency to aggregate. The reaction mechanism of ZnO formation was proposed on the basis of a model system of the base-mediated conversion of a monomer zinc dimethacrylate Zn(MA)2.
Keywords: ZnO; Nanoparticles; Polymer precursor; Hybrid material
Chemical and nanomechanical analysis of rice husk modified by ATRP-grafted oligomer
by Samir M. Morsi; Anahita Pakzad; Amal Amin; Reza S. Yassar; Patricia A. Heiden (pp. 377-385).
Rice husk residues were reacted to produce a heterogeneous ATRP-active multifunctional initiator that was further reacted to give different surfaces.Display Omitted► Synthesis of ATRP-active macroinitiator on surface of rice husk. ► Synthesis of amphiphilic block copolymer by grafting from rice husk surface. ► Rice husk with structured interface. ► Nanomechanical characterization of ATRP-grafted rice husk. ► XPS characterization of ATRP-grafted rice husk.Rice husk (RH), an abundant agricultural residue, was reacted with 2-bromoisobutyryl bromide, to convert it to a heterogeneous polyfunctional macroinitiator for Atom Transfer Radical Polymerization (ATRP). The number of active sites placed on the RH surface was small, but they were ATRP active. Non-polar methyl methacrylate (MMA) and polar acrylonitrile (AN) were polymerized from the RH, and a sequential monomer addition was used to prepare an amphiphilic PMMA-b-PAN copolymer on RH surface. FTIR qualitatively confirmed the grafting. Gravimetric and XPS analysis of the different RH surface compositions indicated thin layers of oligomeric PMMA, PAN, and PMMA-b-PAN. The modified surfaces were mapped by nanomechanical AFM to measure surface roughness, and adhesion and moduli using the Derjaguin–Muller–Toropov model. RH grafted with MMA possessed a roughness value of 7.92, and a hard and weakly adhering surface (13.1GPa and 16.7nN respectively) while RH grafted with AN yielded a roughness value of 29 with hardness and adhesion values of 4.0GPa and 23.5nN. The PMMA-b-PAN modification afforded a surface with a roughness value of 51.5nm, with hardness and adhesion values of 3.0GPa and 75.3nN.
Keywords: Rice husk; Nanomechanical; Heterogeneous ATRP; Macroinitiator; Surface modification; Grafting
Preparation and characterization of zwitterionic surfactant-modified montmorillonites
by Jianxi Zhu; Yanhong Qing; Tong Wang; Runliang Zhu; Jingming Wei; Qi Tao; Peng Yuan; Hongping He (pp. 386-392).
XRD measurements verified that zwitterionic surfactant could be intercalated into the interlayer spaces of montmorillonite and causing interlayer space-swelling.Display Omitted► Zwitterionic surfactants can be intercalated into the montmorillonites. ► Structural characteristics of organo-montmorillonites are examined. ► Increasing surfactant concentration will increase the basal spacing. ► Increasing surfactant alkyl chain length will increase the basal spacing.A series of zwitterionic surfactant-modified montmorillonites (ZSMMs) were synthesized using montmorillonite and three zwitterionic surfactants with different alkyl chain lengths at different concentrations [0.2–4.0 cation exchange capacity (CEC)]. These ZSMMs were characterized by X-ray diffraction (XRD), thermo-gravimetric analysis and differential thermo-gravimetric (TG/DTG) analyses. The zwitterionic surfactant could be intercalated into the interlayer spaces of montmorillonites and causing interlayer space-swelling. From XRD measurements, the amount of the surfactants loaded and the basal spacing increased with surfactant concentration and alkyl chain length. One endothermic DTG peak occurred at ∼390°C, which was assigned to the decomposition of the zwitterionic surfactant on the organo-montmorillonites from 0.2 to 0.6 CEC. When the surfactant loading was increased, a new endothermic peak appeared at ∼340°C. From the microstructures of these ZSMMs, the mechanism of zwitterionic surfactant adsorption was proposed. At relatively low loadings of the zwitterionic surfactant, most of surfactants enter the spacing by an ion-exchange mechanism and are adsorbed onto the interlayer cation sites. When the concentration of the zwitterionic surfactant exceeds the CEC of montmorillonite, the surfactant molecules then adhere to the surface-adsorbed surfactant. Some surfactants enter the interlayers, whereas the others are attached to the clay surface. When the concentration of surfactant increases further beyond 2.0 CEC, the surfactants may occupy the inter-particle space within the house-of-cards aggregate structure.
Keywords: Zwitterionic surfactants; Organo-montmorillonites; Basal spacing; Microstructure
Controlling the size and morphology of anisotropic nanostructures of nickel borate using microemulsions and their magnetic properties
by Menaka; Soma Sharma; Kandalam V. Ramanujachary; Samuel E. Lofland; Ashok K. Ganguli (pp. 393-397).
The reverse micellar route has been used to control the shape and size of anisotropic nickel borate particles. The nanorods of lower diameter show four fold enhancement in magnetization.Display Omitted► The reverse micellar route has been used to control the shape and size of nickel borate nanoparticles. ► Uniform nanorods and nano-spindles of nickel borate have been synthesized for the first time. ► A magnetization enhancement of four fold was found in the surfactant mediated process.Anisotropic nanostructures of nickel borate with controlled size and morphology have been synthesized by a precursor-mediated route. The nickel boron precursor has been synthesized using microemulsions using Tergitol as a surfactant. Microemulsions with various co-surfactants (1-butanol, 1-hexanol and 1-octanol) have been used to obtain uniform nanorods (dia 3–5nm, length 25nm) and nanospindles (dia 30nm, length 400nm). A higher chain length of the co-surfactant (octanol) leads to more uniform rods rather than spindles (butanol). These nanorods show antiferromagnetic behavior with the Néel temperature ranging from 44 to 47K. Though there is no marked variation in Nėel temperature, the magnetic moment increases drastically with the anisotropy of nanorods (thinner rods).
Keywords: Reverse micellar route; Co-surfactant; Nanorods; Nanospindles; Nickel borate
Transport behavior of humic acid-modified nano-hydroxyapatite in saturated packed column: Effects of Cu, ionic strength, and ionic composition
by Dengjun Wang; Lingyang Chu; Marcos Paradelo; Willie J.G.M. Peijnenburg; Yujun Wang; Dongmei Zhou (pp. 398-407).
Representative breakthrough curves of nHAP as a function of pore volumes (PVs) at varying Cu concentrations (a) at pH 6.0, KCl concentrations (b) at pH 5.8±0.2, and CaCl2 concentrations (c) at pH 5.8±0.1 in the presence of 10mgL−1 HA. Each data point represents the average value determined from all experiments conducted at a given IS.Display Omitted► Divalent cations have a strong effect on the deposition of humic acid-modified nano-hydroxyapatite (nHAP). ► Divalent Ca2+ cation bridges the humic acid-modified nHAP and causes greater deposition than monovalent Na+ cation. ► Cu2+ cation has a greater effect on the deposition of humic acid-modified nHAP than Ca2+ cation due to their strong exchange with Ca2+ of nHAP and its surface complexation with nHAP.The surfaces of nano-hydroxyapatite (nHAP) used for contaminated soil and groundwater remediation may be modified to render nHAP highly mobile in the subsurface. Humic acid (HA) is widely used to modify and stabilize colloid suspensions. In this work, column experiments were conducted to determine the effects of contaminant (e.g., Cu) concentration, ionic strength (IS), and ion composition (IC) on the transport behavior of HA-modified nHAP in saturated packed columns. IS and nature of the cation had strong effects on the deposition of nHAP, and the effect was greater for divalent than for monovalent cations. Divalent cations have a greater capacity to screen the surface charge of nHAP, and Ca2+ bridges the HA-modified nHAP colloidal particles, which causes greater deposition. Moreover, Cu2+ had a greater effect on the transport behavior than Ca2+ due to their strong exchange with Ca2+ of nHAP and its surface complexation with nHAP. The relative travel distanceL T, of the injected HA-modified nHAP colloids, ranges from less than one to several meters at varying Cu concentrations, ISs, and ICs in saturated packed columns. The results are crucial to evaluate the efficacy of nHAP on the remediation of contaminated soil and groundwater environments.
Keywords: Nano-hydroxyapatite (nHAP); Humic acid (HA); Cu; Ionic strength (IS); Ionic composition (IC)
Preparation and characterization of silica aquasols
by Karl Bredereck; Franz Effenberger; Michael Tretter (pp. 408-414).
Hydrolysis of tetraethoxy silane (TEOS) in water under rigorously stirring gives an emulsion of TEOS droplets (1–8μm size), which disappear by adding a catalyst (HCL, NaOH or NH3 respectively) to give a nano sized dispersion of silica particles in water.Display Omitted► The first direct preparation of silica aquasols is described. ► Silica nanoparticles were characterized by DLS, REM, NMR and BET. ► The silica aquasols have a high hydrophilizing effect on hydrophobic textile fabrics.Aquasols containing silica nanoparticles with diameters of 75 to 95nm were obtained directly by hydrolysis of 2wt.% tetraethoxysilane (TEOS) in water in the presence of a non-ionic surfactant. The reaction was catalyzed by hydrochloric acid, ammonia, or sodium hydroxide. The particle size, which mainly depends on the concentration of TEOS in water, was determined by dynamic light scattering (DLS). Whereas the catalysts have almost no influence on the particle size, they very strongly affect the morphology of the silica particles formed. The dried SiO2 particles obtained via the HCl-catalyzed reaction have film-forming properties and show no measurable BET surface area. SiO2 particles prepared with ammonia as catalyst form nanoporous films on glass, and the BET surface area of the freeze-dried particles is 540m2/g. Using sodium hydroxide as catalyst results in some agglomeration of uniform spherical particles with a BET surface area of 237m2/g.29Si MAS NMR investigations of the freeze-dried particles provide information about the degree of condensation and the ratio of “free” hydroxyl groups. The silica aquasols described have a surprisingly high hydrophilizing effect on hydrophobic fibers (PP, PET). Silica nanoparticles of comparable diameters, prepared by the “Stöber method”, dispersed in alcohol do not show any hydrophilizing properties worth to mention.
Keywords: Silica nanoparticles; Tetraalkoxysilanes; Aquasols; Hydrophilizing effect
Preparation of poly(methyl methacrylate) grafted hydroxyapatite nanoparticles via reverse ATRP
by Yan Wang; Yan Xiao; Xiujuan Huang; Meidong Lang (pp. 415-421).
Compared with HAP nanoparticles, the dispersibility of surface-grafted HAP with PMMA was significantly improved.Display Omitted► Reverse ATRP was used to synthesis HAP particles grafted with poly(methyl methacrylate). ► The surface-grafted HAP showed excellent dispersibility in MMA monomer. ► The compressive strength of HAP/PMMA composites was improved. ► This approach can give HAP nanoparticles novel properties for perspective applications.Surface-initiated reverse atom transfer radical polymerization (reverse ATRP) technical was successfully employed to modify hydroxyapatite (HAP) nanoparticles with poly(methyl methacrylate) (PMMA). The peroxide initiator moiety for reverse ATRP was covalently attached to the HAP surface through the surface hydroxyl groups. Reverse ATRP of methyl methacrylate (MMA) from the initiator-functionalized HAP was carried out, and the end bromide groups of grafted PMMA initiated ATRP of MMA subsequently. Fourier transformation infrared (FTIR) spectroscopy, thermal gravimetric analysis (TGA) and transmission electron microscopy (TEM) were employed to confirm the grafting and to characterize the nanoparticle structure. The grafted PMMA gave HAP nanoparticles excellent dispersibility in MMA monomer. As the amount of grafted PMMA increased, the dispersibility of surface-grafted HAP and the compressive strength of HAP/PMMA composites were improved.
Keywords: Hydroxyapatite; Surface grafting; Reverse ATRP; Poly(methyl methacrylate)
Self-assembly of gold nanoparticles on functional organic molecular crystals
by Silvia Trabattoni; Massimo Moret; Luciano Miozzo; Marcello Campione (pp. 422-429).
The strong interaction between Au nanoparticles (NPs) and S atoms promotes the adsorption of NPs at the crystal surface of 1,2,3,4-tetrafluoro-7-thiomethyl-acridine, as shown in AFM image (1×1 μm2).Display Omitted► NP depositions were carried out on two isostructural tetrafluoroacridine crystals. ► Gold nanoparticles adsorb on organic crystal surface, thanks to S–Au interaction. ► The substrate coverage, determined by AFM measurements, reaches value up to 13%. ► NPs distribute on the surface uniformly, and aggregates appear increasing deposition time. ► Deposition and imaging have been done simultaneously by AFM equipped with fluid cell.The utilization of metal nanoparticles (NPs) to fabricate metal electrodes under mild conditions is one of the most studied topic in recent years. In this work, colloidal Au NPs were deposited on two isostructural molecular crystals, namely 1,2,3,4-tetrafluoro-7-thiomethyl-acridine (MeSAcr) and 1,2,3,4-tetrafluoro-7-methoxy-acridine (MeOAcr), exposing S atoms and O atoms, respectively, at their largest crystal faces. The depositions were carried out mainly by drop casting under ambient conditions, increasing the contact time from 1 to 120min, and the samples were then analyzed by atomic force microscopy (AFM) to evaluate the coverage. Thanks to the affinity between S and Au atoms, Au NPs are observed to adhere on the MeSAcr surface within 1-min contact time, whereas at least 1h is required to find NPs on the MeOAcr surface. NP adsorption is also affected by the substrate surface morphology; indeed, step edges represent preferential adsorption sites even in the absence of Au–S interaction. Experiments under different conditions were performed to maximize the coverage on MeSAcr, reaching values up to 13%. AFM equipped with fluid cell was also employed to simultaneously depositing and imaging NPs, achieving a better understanding of the adsorption mechanism.
Keywords: Gold nanoparticle; Organic crystal; Atomic force microscopy; Fluid cell
Effect of Al-doping on the structure and optical properties of electrospun zinc oxide nanofiber films
by Sining Yun; Sangwoo Lim (pp. 430-439).
Changes in the crystallite size, grain size, cell parameter, blueshift of UV peak and the intensity of UV–Vis–NIR emission for AZO correlate with the size effect resulting from impurity incorporation..Display Omitted► AZO nanofibers with various average diameters were fabricated by a simple electrospinning. ► AZO nanofiber films were characterized by the XRD, SEM, EDS, TEM, XPS and PL. ► Al doping causes a decrease trend in the crystallite/grain size and lattice parameter for AZO. ► A blue shift of UV peak is attributed to the size effect and Al-doping or the impurity incorporation. ► Optical properties of AZO nanofiber films can be greatly improved by an appropriate Al doping level.Electrospun ZnO precursor nanofibers of average diameters 122±64nm, 117±44nm and 110±39nm were fabricated by controlling the Al concentration of a polymeric solution. The resulting nanofibers were characterized by the XRD, SEM, EDS, TEM, XPS and PL. The electrospun Al-doped ZnO nanofiber films were polycrystalline and composed of densely packed grains, with crystallite size ranging from 28.7nm, 25.7nm, 25.4nm to 20.4nm corresponding to the atomic concentration of aluminum from 0, 1.6, 2.5 to 5.8at.%. The incorporation of aluminum resulted in a decrease trend in the grain size and lattice parameter of the ZnO nanofiber films. The room temperature PL spectra of all samples show three different emissions, including UV (ultraviolet) emission with an obvious blue shift, Vis (visible) emission and NIR (near infrared) emission, the intensity of which decreases monotonically as the doping concentration is increased except for the highest doping level. The impurity content correlates with changes in the PL spectra, and the appropriate Al doping can improve the optical properties of ZnO nanofibers. The small size effect and Al-doping or the impurity incorporation should be responsible for the blue shift observation in Al-doped ZnO nanofiber films.
Keywords: AZO nanofibers; Electrospinning; Morphologies; Crystal structure; Optical properties
Characterisation of organoclays and adsorption of p-nitrophenol: Environmental application
by Yuri Park; Godwin A. Ayoko; Ray L. Frost (pp. 440-456).
N2 adsorption–desorption measurements of the clay and organoclays show that the loaded surfactant is highly important in determining the mechanisms of p-nitrophenol sorption onto organoclays.Display Omitted► The expansions of organoclays with and without adsorbed p-nitrophenol were investigated. ► X-ray photoelectron spectroscopy showed that structural changes occurred within the interlayer of the organoclays. ► TEM images of the organoclays were not only linear but curved or bent. ► This research provides important information on the mechanisms for the adsorption of organic molecules on organoclays.Organoclays were synthesised through ion exchange of a single surfactant for sodium ions, and characterised by a range of method including X-ray diffraction (XRD), BET, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM). The change in surface properties of montmorillonite and organoclays intercalated with the surfactant, tetradecyltrimethylammonium bromide (TDTMA) were determined using XRD through the change in basal spacing and the expansion occurred by the adsorbed p-nitrophenol. The changes of interlayer spacing were observed in TEM. In addition, the surface measurement such as specific surface area and pore volume was measured and calculated using BET method, this suggested the loaded surfactant is highly important to determine the sorption mechanism onto organoclays. The collected results of XPS provided the chemical composition of montmorillonite and organoclays, and the high-resolution XPS spectra offered the chemical states of prepared organoclays with binding energy. Using TGA and FT-IR, the confirmation of intercalated surfactant was investigated. The collected data from various techniques enable an understanding of the changes in structure and surface properties. This study is of importance to provide mechanisms for the adsorption of organic molecules, especially in contaminated environmental sites and polluted waters.
Keywords: Organoclay; X-ray photoelectron spectroscopy; Montmorillonite; Surfactant; BET
Low-temperature synthesis of nanoparticle-assembled, transparent, and low-crystallized hydroxyapatite blocks
by Masahiro Okada; Tsutomu Furuzono (pp. 457-462).
A general casting method on solid substrates and a novel casting method on flowable substrates to fabricate crack-free nanoparticle-assembled blocks of low-crystallized hydroxyapatite.Display Omitted► Transparent blocks were assembled with low-crystallized hydroxyapatite nanoparticles. ► A crack-free nanoparticle-assembled block was fabricated by a novel casting method on flowable substrates. ► The nanoparticle-assembled transparent HAp had nanosized pores among the particles.The conditions for preparing transparent blocks assembled with low-crystallized hydroxyapatite (HAp) nanoparticles were examined. An aqueous dispersion of 32-nm-sized HAp nanoparticles was prepared by a wet chemical process at room temperature (18–22°C), and then the nanoparticle-assembled block was prepared by casting the dispersion at 60°C. We also proposed a novel casting method on flowable substrates to fabricate crack-free nanoparticle-assembled blocks, because large and thick blocks were not obtained by a conventional casting method on solid substrates due to crack formation. The nanoparticle-assembled transparent HAp had nanosized pores among the particles. Cell adhesion and proliferation on the block could be directly observed with an optical microscope.
Keywords: Hydroxyapatite; Nanoparticle; Assembly; Transparent; Nanopore; Cell adhesion
Synthesis and characterization of silver nanoparticle and graphene oxide nanosheet composites as a bactericidal agent for water disinfection
by Qi Bao; Dun Zhang; Peng Qi (pp. 463-470).
Ag NP/GO nanocomposites have been synthesized by the in situ reduction with hydroquinone and can be used as a bacteria killer or to prepare paper like materials.Display Omitted► Nanocomposites were prepared via in situ reduction of silver on graphene oxide nanosheets. ► The presence of silver nanoparticles is evidenced by a change in the physicochemical property of graphene oxide. ► Graphene oxide’s antibacterial ability is greatly enhanced. ► Bacterial inactivation of the composites is retained in aquatic media.Graphene oxide (GO) nanosheets impregnated with silver nanoparticles (Ag NPs) were fabricated by the in situ reduction of adsorbed Ag+ by hydroquinone (HQ) in a citrate buffer solution. Paper-like Ag NP/GO composite materials were fabricated owing to convenient structure characterization and antibacterial tests. The Ag NP/GO composites were characterized by UV–vis spectra, transmission electron microscope, electron diffraction, Raman spectroscopy, and field emission scanning electron microscope coupled with Energy Dispersive Spectrometer. Antibacterial activity was tested using Escherichia coli and Staphylococcus aureus as model strains of Gram negative and Gram positive bacteria, respectively. The as-prepared composites exhibit stronger antibacterial activity against both. The Ag NP/GO composites performed efficiently in bringing down the count of E. coli from 106cfu/mL to zero with 45mg/L GO in water. The micron-scale GO nanosheets (lateral size) enable them to be easily deposited on porous ceramic membranes during water filtration; making them a promising biocidal material for water disinfection.
Keywords: Silver nanoparticle; Graphene oxide nanosheet; Nanocomposites; Antibacterial; Disinfection; Paper-like material
Preparation and characterization of highly stable lipid nanoparticles with amorphous core of tuneable viscosity
by Thomas Delmas; Anne-Claude Couffin; Pierre Alain Bayle; François de Crécy; Emmanuelle Neumann; Françoise Vinet; Michel Bardet; Jérôme Bibette; Isabelle Texier (pp. 471-481).
Fluid or gel formulations of stable lipid nanoparticles with a non-crystalline core, whose viscosity can be finely tuned by the lipid composition and the temperature, are described.Display Omitted► Fluid or gel formulations of stable lipid nanoparticles are achieved. ► The nanoparticle core is non-crystalline. ► The core viscosity can be tuned by the lipid composition and the temperature. ► A design of experiments investigates the limits of the system colloidal stability.Lipid nanoparticles (LNP) have been designed based on low cost and human-use approved excipients, and manufactured by an easy, robust, and up-scalable process. Fluid colloidal dispersions or gel viscous formulations of highly stable nanoparticles (more than 12month stability is achieved for some formulations) can be obtained. Their physicochemical properties are studied by Dynamic Light Scattering, Differential Scanning Calorimetry, and NMR. The results picture nanoparticles with a non-crystalline core, which viscosity can be finely tuned by the lipid composition and the temperature. A design of experiments has been used to investigate the limits of the system colloidal stability. The impact of core and surfactant weight fractions have been explored both experimentally and using the design of experiments. The versatility of this physicochemical system could open the way to a wide range of future pharmaceutical applications.
Keywords: Lipid nanoparticle; Amorphous system; Physical stability; Design of experiments
Detection of proteins on Silica–Silver Core–Shell substrates by surface-enhanced Raman spectroscopy
by Lei Chen; Xiaoxia Han; Jingxiu Yang; Ji Zhou; Wei Song; Bing Zhao; Weiqing Xu; Yukihiro Ozaki (pp. 482-487).
The proposed SSCS SERS-active substrates for four model proteins detection, atto610-biotin/avidin complex, fluorescein isothiocyanate (FITC)-anti human IgG, cytochrome c and lysozyme.Display Omitted► A SSCS substrate with aggregated Ag nanoparticles shell has been developed. ► This substrate exhibits strong SERS activity for label and label-free proteins. ► The SERS substrate is useful to investigate the protein structure and interaction.We have employed the proposed Silica–Silver Core–Shell (SSCS) SERS-active substrates to detect four model proteins: lysozyme (a protein without chromophore), cytochrome c (a protein with chromophore of heme), fluorescein isothiocyanate (FITC)-anti human IgG (labeled with FITC) and atto610-biotin/avidin (recognition with labeled small molecules). SERS spectra of these proteins and Raman labels on the SSCS substrates show both high sensitivity and reproducibility, which are due to electromagnetic SERS enhancement with additional localization field within closely packed Ag nanoparticles decorated on the SiO2 nanoparticles and the aggregation of SiO2@Ag particles. We have found that the SERS intensities of atto610-biotin/avidin adsorbed on the SSCS substrates are about 20 times stronger than those from Ag plating on Au-decorated substrate. Moreover, the broad surface plasmon resonance (SPR) of the proposed substrates will extend SERS applications to more biological molecules with different laser excitations.
Keywords: SSCS substrate; SERS; Protein detection
Poly(lactic acid)-coated mesoporous silica nanosphere for controlled release of venlafaxine
by Jing Tang; Igor I. Slowing; Yulin Huang; Brian G. Trewyn; Jun Hu; Honglai Liu; Victor S.-Y. Lin (pp. 488-496).
A possible schematic process of the drug venlafaxine released from two types of mesoporous nanospheres, DH-MSN and CA-PLA-MSN, in SGF, in SGA, and in SIF without pancreatin.Display Omitted► Cholic acid-crosslinked poly(lactic acid) was synthesized as pore block. ► Poly(lactic acid) layer could delay the release of venlafaxine in the beginning. ► Pepsin would stick on the surface of deliveries to reduce release rate.Two types of mesoporous silica nanospheres (MSNs) were synthesized for use as controlled-release agents. One was prepared by grafting with 5,6-dihydroxyhexylsilane (DH-MSN) and the other one by further coating with cholic acid-crosslinked poly(lactic acid) (CA-PLA-MSN). We studied the release of the antidepressant venlafaxine from each of the materials in simulated gastric fluid (SGF), in simulated gastric acid solution (SGA), and in simulated intestinal fluid without pancreatin (SIF). The CA-PLA-MSN material was able to significantly delay the release of the drug in intestinal condition compared with gastric acid surrounding due to the fast decomposition rate of PLA in gastric acid. Moreover, it successfully avoided the initial burst to a certain extent in SGF. The enzyme pepsin played a favorable obstruct role in both DH-MSN and CA-PLA-MSN systems to reduce release rate. A model based on Weibull model was built to fit the release results, and based on it, the mechanisms about release processes were brought out tentatively.
Keywords: Venlafaxine; Mesoporous materials; Controlled release
Growth, stability, optical and photoluminescent properties of aqueous colloidal ZnS nanoparticles in relation to surfactant molecular structure
by S.K. Mehta; Sanjay Kumar; Michael Gradzielski (pp. 497-507).
Aqueous dispersions of ZnS nanoparticles were stabilized with different cationic and anionic surfactants. The as-prepared nanoparticles exhibited surfactant structure dependent optical and photoluminescence properties.Display Omitted► Influence of various cationic and anionic surfactants as surface modifiers on synthesis of colloidal ZnS nanoparticles (NPs) has been compared. ► The tendency of the cationic surfactants to stabilize the ZnS NPs decreases with decreasing their hydrocarbon chain length. ► The anionic surfactants have been proven to be better stabilizing agents as compared to cationic surfactants of same hydrocarbon chain length. ► The growth behavior of ZnS NPs, as evident from red shift in absorption spectra has been found to be quite different in all the six surfactants. ► In presence of anionic surfactants, the whole absorption spectra of ZnS NPs witnessed prominent red shift with time indicating particle growth.The interaction between organic molecules and the surface of nanoparticles (NPs) strongly affects the size, properties and applications of surface-modified metal sulfide semiconductor nanocrystals. From this viewpoint, we compared the influence of cationic surfactants with various chain lengths and anionic surfactants with different head groups, as surface modifiers during synthesis of ZnS NPs in aqueous medium. The surfactant adsorbs on the surface of the particles as micelle-like aggregates. These aggregates can form even at the concentration lower than critical micelle concentration (cmc) due to interaction between the polar groups and the NPs. The nature of interaction depends specifically on the surfactant polar group. The ability of surfactant to form the micelle-like aggregates on the surface of the NPs correlates with their cmc. This leads to the fact that the surfactant with longer tail stabilizes the NPs better since its cmc is lower. The adsorption of the surfactant on the NPs also stabilizes them by the change of their charge which is in accordance with the correlation of zeta potential with the particles stability. The energetics of surface states generating interesting photoluminescence (PL) properties in ZnS NPs has been governed by the nature of surfactant molecules. In general, the size, structure, and stability of the ZnS NPs can be controlled by the choice of suitable surfactant.
Keywords: ZnS; Surfactants; Adsorption; Ostwald ripening; Photoluminescence; Zeta potential
The effect of copper on the precipitation of scorodite (FeAsO4·2H2O) under hydrothermal conditions: Evidence for a hydrated copper containing ferric arsenate sulfate-short lived intermediate
by M.A. Gomez; L. Becze; M. Celikin; G.P. Demopoulos (pp. 508-518).
The effect of copper on arsenic fixation via the formation of scorodite (FeAsO4·2H2O) and the formation of a hydrated ferric cupric arsenate sulfate short lived intermediate are reported.Display Omitted► Scorodite was found to form at T >138 C and >90min independent of the presence or absence of copper sulfate in the solution. ► At <96 min and 138 C an intermediate copper containing ferric arsenate sulfate phase was observed for the first time. ► Excess ferric sulfate was found to slow down the full development of H-bond structure in scorodite. ► Analysis of an industrial residue found the arsenate environment to be similar to that of intermediate basic ferric arsenate sulfate (BFAS).The effect of copper sulfate on scorodite precipitation and its mechanism of formation at 150°C was investigated. Scorodite was determined to be the dominant phase formed under all conditions explored (0.614)1.5, 0–0.3M CuSO4, 0–0.3M MgSO4, at 2.5h and 150°C). The produced scorodite was found to incorporate up to 5% SO4 and ⩽1% Cu or Mg in its structure. The precipitation of scorodite was stoichiometric, i.e. the Fe/As molar ratio in the solids was equal to one independent of the starting Fe/As ratio in the solution. The presence of excess ferric sulfate in the initial solution (Fe/As>1) was found to slow down the ordering of the H-bond structure in scorodite. Precipitation under equimolar concentrations (As=Fe=Cu=0.3M), short times and lower temperatures (30–70min and 90–130°C) revealed the formation of a Cu–Fe–AsO4–SO4–H2O short lived gelatinous intermediate that closely resembled the basic ferric arsenate sulfate (BFAS) type of phase, before ultimately converting fully to the most stable scorodite phase (96min and 138°C). This phase transition has been traced throughout the reaction via elemental (ICP-AES, XPS), structural (PXRD, TEM) and molecular (ATR-IR, Raman) analysis. ATR-IR investigation of an arsenic containing industrial residue produced during pressure leaching of a copper concentrate (1h and 150°C) found evidence of the formation of an arsenate mineral form resembling the intermediate basic ferric arsenate sulfate phase.
Keywords: Scorodite; Arsenic; Pressure leaching; Copper; Gelatinous intermediate; Basic ferric arsenate sulfate; XPS; ATR-IR; Raman
Avidin/PSS membrane microcapsules with biotin-binding activity
by Yoshihiro Endo; Katsuhiko Sato; Kentaro Sugimoto; Jun-ichi Anzai (pp. 519-524).
Avidin/PSS microcapsules prepared through a layer-by-layer deposition exhibit biotin-binding activity.Display Omitted► Polyelectrolyte microcapsules with avidin/PSS membrane were prepared. ► The uptake and release of biotin-labeled FITC (b-FITC) to the capsule were studied. ► The capsule was modified with b-GOD with retaining its catalytic activity.Polyelectrolyte microcapsules with avidin-poly(styrene sulfonate) (PSS) membrane were prepared by a layer-by-layer deposition technique. The uptake and release of biotin-labeled fluorescein (b-FITC) as well as immobilization of biotin-labeled glucose oxidase (b-GOx) to the microcapsule were studied. The polyelectrolyte microcapsules were prepared by coating the surface of calcium carbonate (CaCO3) microparticles with an avidin/PSS multilayer membrane, followed by dissolution of CaCO3 core in an ethylenediaminetetraacetic acid solution. Inner and outer poly(allylamine)/PSS films were required to isolate the microcapsules, whereas microcapsules could not be formed without the support. The uptake of b-FITC into the microcapsule was highly enhanced through a strong binding of b-FITC to avidin as compared with the uptake of biotin-free FITC. Release of b-FITC from the microcapsule was accelerated upon addition of biotin due to a competitive binding of the added biotin to the binding site of avidin. Similarly, the surface of microcapsule was modified with b-GOx with retaining its catalytic activity.
Keywords: Polyelectrolyte microcapsule; Layer-by-layer film; Avidin; Biotin; Uptake and release; Glucose oxidase
The interactions between doxorubicin and amphiphilic and acidic β-sheet peptides towards drug delivery hydrogels
by Shlomo Zarzhitsky; Hanna Rapaport (pp. 525-531).
The amphiphilic peptidePro-Asp-(Phe-Asp)5-Pro and doxorubicin (DOX) form injectable hydrogels composed of β-sheet fibrils that may be utilized as sustained delivery platform in treatment of bone cancers.Display Omitted► Amphiphilic and acidic β-sheet peptides interact by electrostatic and hydrophobic interactions with the chemotherapeutic drug, doxorubicin. ► The peptide hydrogels were found to release doxorubicin in a sustained and controllable manner. ► Released drug was found to maintain its cytotoxic activity in vitro on osteosarcoma cell line.Amphiphilic β-sheet peptides decorated by acidic amino acids may spontaneously assemble into ordered monolayers at interfaces as well as form hydrogels at near physiological pH values. Here we monitored interactions between the peptide Pro-Asp-(Phe-Asp)5-Pro and the mildly amphiphilic chemotherapeutic drug doxorubicin (Dox). The peptide in the form of monolayers at the air water interface was found to enhance Dox adsorption, pointing to favorable interactions between the amphiphilic peptide and Dox. In solutions the fluorescence emission of Dox which was fitted to the Stern–Volmer quenching models suggested the formation of Dox associated forms >25μM and larger forms at >100μM. In presence of the peptide these larger associated forms appeared already at Dox concentrations >50μM, indicating enhanced interactions between Dox and the peptide in the β-sheet conformation. Peptide hydrogels loaded with the drug showed sustained release profiles over several days. Smaller fractions of the drug were released with increase in either peptide or initially loaded drug concentrations. The released Dox was found to retain its cytotoxic activity in vitro. This study provides insights on the interactions between the amphiphilic and acidic peptide and Dox that are useful for the bottom up development of Dox-loaded peptide hydrogels for local drug delivery applications.
Keywords: Peptide monolayers; Drug-delivery; Hydrogels; Doxorubicin; Peptides self-assembly
Layered zinc hydroxide salts: Delamination, preferred orientation of hydroxide lamellae, and formation of ZnO nanodiscs
by Jan Demel; Josef Pleštil; Petr Bezdička; Pavel Janda; Mariana Klementová; Kamil Lang (pp. 532-539).
Layered zinc hydroxide salts are transformed in one step into the hydroxide lamellae dispersed in solvent and anisotropic ZnO nanoparticles.Display Omitted► Layered zinc hydroxide salts (LZH) are delaminated into individual lamellae. ► LZH intercalated with dodecyl sulfate anions are delaminated in butanol to ca. 10-20nm hydroxide lamellae. ► LZH nitrate treated in formamide yield lamellae with a size between 73.3nm and 10nm, affected by aging, having a thickness between 2.6 and 3.8nm. ► LZH intercalated with dodecyl sulfate anions are transformed to anisotropic disc-like nanoparticles of ZnO flattened along the (001) plane.Delamination of layered zinc hydroxide salts (LZH) into hydroxide layers provides nanobuilding blocs of a two-dimensional anisotropy. The methodology, extent of delamination, the size and stability of hydroxide lamellae are described in detail. The ability of lamellae to restack to form oriented hydroxide films depends on the solvent, original LZH salt, and conditions used for delamination. The most interesting results were obtained using LZH intercalated with dodecyl sulfate anions and LZH nitrate delaminated in butanol at 60°C and in formamide at room temperature, respectively. The former method produces hydroxide lamellae of a lateral size of ca. 10–20nm. The inner structure of the hydroxide layers is conserved and separated lamellae restack to the original layered structure of LZH dodecyl sulfate. The latter method yields lamellae with a size decreasing from 73.3nm to 10nm after a 2-week aging, while their thickness is nearly constant (2.6–3.8nm). However, the use of formamide is complicated by the formation of Zn(II) formate. The major part of LZH intercalated with dodecyl sulfate anions is transformed during the delamination procedure to anisotropic ZnO nanoparticles, either needle-like particles prolonged in the  direction or disc-like particles flattened along the (001) plane.
Keywords: Layered zinc hydroxide; Delamination; Exfoliation; Hydroxide layer; ZnO
A controlled approach to iron oxide nanoparticles functionalization for magnetic polymer brushes
by Francesco Galeotti; Fabio Bertini; Guido Scavia; Alberto Bolognesi (pp. 540-547).
Well-controlled surface modification of magnetite nanoparticles is achieved by accurate TGA monitoring, facilitating the realization of magnetic polymer brushes.Display Omitted► Magnetic nanoparticles surface modification with three different organosilanes. ► Thermogravimetric study to set the best reaction conditions. ► Grafting density up to 7molecules per nm2 obtained. ► Facile formation of dense PMMA magnetic brushes.In this article, we report a detailed study of surface modification of magnetite nanoparticles by means of three different grafting agents, functional for the preparation of magnetic polymer brushes. 3-Aminopropyltriethoxysilane (APTES), 3-chloropropyltriethoxysilane (CPTES), and 2-(4-chlorosulfonylphenyl)ethyltrichlorosilane (CTCS) were chosen as grafting models through which a wide range of polymer brushes can be obtained. By means of accurate thermogravimetric analysis a good control over the amount of immobilized molecules is achieved, and optimal operating conditions for each grafting agent are consequently determined. Graft densities ranging from approximately 4 to 7molecules per nm2 are obtained, depending on the conditions used. In addition, the surface-initiated atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) carried out with CTCS-coated nanoparticles is presented as an example of polymer brushes, leading to a well-defined and dense polymeric coating of around 0.6PMMA chains per nm2.
Keywords: Magnetite nanoparticle; Surface modification; Polymer brush
Mechanisms of TiO2 nanoparticle transport in porous media: Role of solution chemistry, nanoparticle concentration, and flowrate
by Indranil Chowdhury; Yongsuk Hong; Ryan J. Honda; Sharon L. Walker (pp. 548-555).
A complex combination of mechanisms involving DLVO-type interactions, aggregation, straining, blocking, and aggregate breakup can dominate the transport and removal of nano-TiO2 through porous media.Display Omitted► Removal mechanisms depend on nanoparticle concentration, flowrate, pH and ionic strength. ► Combination of mechanisms including straining, blocking, and aggregate breakup. ► Aggregate size is important parameter for removal under unfavorable conditions. ► Under favorable conditions, blocking leads to greater elution with nanoparticle concentration. ► Increased flowrate leads to more elution due to aggregate breakup.The role of solution chemistry, nanoparticle concentration and hydrodynamic effects in the transport and deposition of TiO2 nanoparticles through porous media has been systematically investigated. Two solution chemistry variables, pH and ionic strength (IS), showed a significant influence on the transport due to their involvement in the aggregation of the nanoparticles and interaction with quartz sand. An electrostatically unfavorable condition for deposition existed at pH 7, at which the greatest retention occurred in the column, likely due to aggregation (>1000nm) and straining effects. Under electrostatically favorable conditions (pH 5) significant elution from the column was observed and attributed to smaller aggregate size (∼300nm) and blocking effects. Nanoparticle concentration was found to contribute to the increased breakthrough of nanoparticles at pH 5 due to blocking and subsequent particle–particle repulsion. Increased flowrate resulted in greater elution of nanoparticles due to hydrodynamic forces acting on aggregates and subsequently contributed to blocking. Overall, a combination of mechanisms including straining, blocking, and DLVO-type forces were involved over the range of solution chemistry and nanoparticle concentrations tested. Consideration of these mechanisms is necessary for improved removal of TiO2 nanoparticles via filtration and reliable prediction of transport of these potentially problematic nanoparticles through the subsurface.
Keywords: Titanium dioxide; Transport; Porous media; Mechanisms; Nanoparticle concentration; Hydrodynamic effects
Highly temperature responsive core–shell magnetic particles: Synthesis, characterization and colloidal properties
by Md Mahbubor Rahman; Mohamed M. Chehimi; Hatem Fessi; Abdelhamid Elaissari (pp. 556-564).
Schematic representation of the temperature responsive core-shell magnetic particles preparation by seed emulsion polymerization using oil in water magnetic emulsion as seed.Display Omitted► Temperature responsive magnetic polymer particles were prepared. ► Perfect magnetic core and polymeric shell morphology observed by TEM. ► Hydrodynamic diameter of the particles was decreased with increasing temperature. ► Surface charge property of the particles can be tuned by pH.Temperature responsive magnetic polymer submicron particles were prepared by two step seed emulsion polymerization process. First, magnetic seed polymer particles were obtained by emulsion polymerization of styrene using potassium persulfate (KPS) as an initiator and divinylbenzne (DVB) as a cross-linker in the presence of oil-in-water magnetic emulsion (organic ferrofluid droplets). Thereafter, DVB cross-linked magnetic polymer particles were used as seed in the precipitation polymerization of N-isopropylacrylamide (NIPAM) to induce thermosensitive PNIPAM shell onto the hydrophobic polymer surface of the cross-linked magnetic polymer particles. To impart cationic functional groups in the thermosensitive PNIPAM backbone, the functional monomer aminoethylmethacrylate hydrochloride (AEMH) was used to polymerize with NIPAM while N,N′-methylenebisacrylamide (MBA) and 2, 2′-azobis (2-methylpropionamidine) dihydrochloride (V-50) were used as a cross-linker and as an initiator respectively. The effect of seed to monomer (w/w) ratio along with seed nature on the final particle morphology was investigated. Dynamic light scattering (DLS) results demonstrated particles swelling at below volume phase transition temperature (VPTT) and deswelling above the VPTT. The perfect core (magnetic) shell (polymer) structure of the particles prepared was confirmed by Transmission Electron Microscopy (TEM). The chemical composition of the particles were determined by thermogravimetric analysis (TGA). The effect of temperature, pH, ionic strength on the colloidal properties such as size and zeta potential of the micron sized thermo-sensitive magnetic particles were also studied. In addition, a short mechanistic discussion on the formation of core–shell morphology of magnetic polymer particles has also been discussed.
Keywords: Magnetic emulsion; Core-shell morphology; Temperature responsive; Volume phase transition; pH sensitive; Electrophoretic mobility
Roles of head group architecture and side chain length on colorimetric response of polydiacetylene vesicles to temperature, ethanol and pH
by Nipaphat Charoenthai; Thanutpon Pattanatornchai; Sumrit Wacharasindhu; Mongkol Sukwattanasinitt; Rakchart Traiphol (pp. 565-573).
This contribution demonstrates the colorimetric response of polydiacetylene vesicles to temperature, ethanol and pH varies with structures of their head groups and side chains.Display Omitted► The colorimetric response of polydiacetylene vesicles to different stimuli is investigated. ► Shortening the alkyl side chain leads to a faster colorimetric response. ► Poly(AEPCDA) vesicles exhibit an unusual multi-step color-transition. ► Our results are important for designing functional PDA vesicles.In this contribution, we report the relationship between molecular structures of polydiacetylene (PDA) vesicles, fabricated by using three monomers, 10,12-tricosadiynoic acid (TCDA), 10,12-pentacosadiynoic acid (PCDA) and N-( 2-aminoethyl)pentacosa-10,12-diynamide (AEPCDA), and their color-transition behaviors. The modification of side chain length and head group of the PDA vesicles strongly affects the colorimetric response to temperature, ethanol and pH. A shorter side chain of poly(TCDA) yields weaker inter- and intra-chain dispersion interactions in the bilayers compared to the system of poly(PCDA), which in turn results in a faster color transition upon exposure to all stimuli. A change of head group in poly(AEPCDA) slightly reduces the transition temperature. Interestingly, the colorimetric response of poly(AEPCDA) vesicles to the addition of ethanol is found to occur in a two-step fashion while the response of poly(PCDA) vesicles takes place in a one-step process. The amount of ethanol required for inducing complete color-transition of poly(AEPCDA) vesicles is also much higher, about 87% v/v. The increase of pH to ∼9 and ∼10 causes a color-transition of poly(TCDA) and poly(PCDA) vesicles, respectively. The poly(AEPCDA) vesicles, on the other hand, change color upon decreasing pH to ∼0. The colorimetric response also occurs in a multi-step fashion. These discrepancies are attributed to the architecture of surface layers of poly(AEPCDA), constituting amine and amide groups separated by ethyl linkers.
Keywords: Conjugated polymer; Structural–properties relationship; Optical sensor; Photophysics; Color-transition
CdS nanoparticles deposited on montmorillonite: Preparation, characterization and application for photoreduction of carbon dioxide
by Petr Praus; Ondřej Kozák; Kamila Kočí; Aleš Panáček; Richard Dvorský (pp. 574-579).
TEM micrographs of CdS nanoparticles deposited on montmorillonite.Display Omitted► CdS nanoparticles were precipitated by the reaction of cadmium acetate and sodium sulphide in the presence of cetyltrimethylammonium. ► The nanoparticles of the cubic structure (Hawleite) were deposited on the montmorillonite external surface. ► The size of CdS nanoparticles was calculated from the band-gap energy (2.63eV) at 7nm. ► The micrographs of transmission electron microscopy showed CdS nanoparticles with the size of 5nm. ► The CdS-montmorillonite composite was used for the photoreduction of carbon dioxide forming.CdS nanoparticles were precipitated by the reaction of cadmium acetate with sodium sulphide in the presence of cetyltrimethylammonium (CTA) and deposited on montmorillonite (MMT). The resulting CdS-MMT nanocomposite contained 6wt.% of CdS and 30wt.% of CTA. Band-gap energy of CdS was estimated at 2.63±0.09eV using the Tauc plot. The size of CdS nanoparticles was calculated from the band-gap energy at 5nm and from the micrographs of transmission electron microscopy (TEM) at 5nm. Selected area electron diffraction (SAED) recognized the cubic structure of CdS (Hawleite). The dynamic light scattering (DLS) method confirmed that CdS nanoparticles were anchored on the surface of MMT particles. CTA was found to be intercalated into MMT and adsorbed on its external surface.CdS-MMT was used for the photoreduction of carbon dioxide dissolved in NaOH solutions. The yields of originating gas products can be arranged in the order: H2≫CH4>CO. Amounts of these products were 4–8 folds higher then those obtained with TiO2 Evonic P25. Hydrogen reduced CO2 to CO and CH4.
Keywords: CdS nanoparticles; Montmorillonite; Photoreduction; Carbon dioxide
Charging and stability of anionic latex particles in the presence of linear poly(ethylene imine)
by István Szilágyi; Dana Rosická; José Hierrezuelo; Michal Borkovec (pp. 580-585).
The lack of dependence on the molecular mass of poly(ethylene imine) (LPEI) on colloidal stability reveals that the adsorbed LPEI layer is unusually homogeneous.Display Omitted► Linear poly(ethylene imine) adsorbs strongly on oppositely charged latexes. ► The suspension stability is independent of the molecular mass. ► This independence reveals that the adsorbed layer is laterally homogeneous.Charging properties and colloidal stability of negatively charged polystyrene latex particles were investigated in the presence of linear poly(ethylene imine) (LPEI) of different molecular masses by electrophoresis and dynamic light scattering (DLS). Electrophoretic mobility measurements illustrate that LPEI strongly adsorbs on these particles leading to charge neutralization at isoelectric point (IEP) and charge reversal. Time-resolved DLS experiments indicate that the aggregation of the latex particles is rapid near the IEP and slows down away from this point. Surprisingly, the colloidal stability does not depend on the molecular mass, which indicates that the adsorbed LPEI layer is rather homogeneous.
Keywords: Polyethylenimine; Electrophoresis; Dynamic light scattering; Overcharging; Aggregation; Flocculation; Coagulation
Controllable synthesis and luminescent properties of three-dimensional nanostructured CaWO4:Tb3+ microspheres
by Yue Tian; Baojiu Chen; Hongquan Yu; Ruinian Hua; Xiangping Li; Jiashi Sun; Lihong Cheng; Haiyang Zhong; Jinsu Zhang; Yanfeng Zheng; Tingting Yu; Libo Huang (pp. 586-592).
CaWO4:Tb3+ microspheres assembled by submicrospindles were synthesized via a mild sonochemical route with the aid of surfactant Polyglycol 600. The formation mechanism for the 3D-structured CaWO4:Tb3+ microspheres was studied.Display Omitted► Nanostructured CaWO4:Tb3+ microspheres were self-assembled via a sonochemical route with the aid of PEG-600. ► Formation mechanism of the microspheres was proposed based on the ultrasonic irradiation time experiments. ► Energy transfer processes between Tb3+ ions were studied through analysis on the fluorescence decays.Three-dimensional (3D) nanostructured CaWO4:Tb3+microspheres assembled by submicrospindles were synthesized via a mild sonochemical route from an aqueous solution of CaCl2, TbCl3 and Na2WO4 with the aid of surfactant Polyglycol 600 (PEG-600). The crystal structure and morphology of the as-prepared products were characterized by using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). Rietveld refinement was carried out on the XRD data. The results showed that the CaWO4:Tb3+nanoparticles can be formed without ultrasonic irradiation or addition of PEG-600. With continuously increasing irradiation time the submicrospindles and microspheres could be self-assembled. The central diameter and length of the submicrospindles are around 190 and 500nm, respectively. The 3D CaWO4:Tb3+nanostructured microspheres with diameter of 2–4μm were assembled by the submicrospindles. A possible formation mechanism for the 3D-structured CaWO4:Tb3+microspheres was proposed. The Photoluminescent (PL) properties of Tb3+ions in the nanostructured CaWO4 microspheres were studied. The energy transfer processes in CaWO4:Tb3+microspheres were analyzed. The electric dipole–dipole energy transfers related to5D3 level were studied by inspecting the fluorescence decay of5D3 level. The energy transfer critical distance was estimated.
Keywords: Controllable synthesis; Nanostructure; Assembly; Luminescence; Energy transfer
Sensitive protein microarray synergistically amplified by polymer brush-enhanced immobilizations of both probe and reporter
by Yingshuai Liu; Chun Xian Guo; Weihua Hu; Zhisong Lu; Chang Ming Li (pp. 593-599).
A unique copolymer brush was coated on substrate and silica nanoparticle to efficiently immobilize probe and reporter respectively for synergistic signal amplification of protein microarray.Display Omitted► A copolymer brush was grafted from substrate for efficient probe protein attachment. ► The brush-coated colloidal silica was prepared for high reporter loading. ► Synergistic signal enhancement was achieved by the brush-attached probe and reporter. ► Significantly improved sensitivity was demonstrated using microarray immunoassay.Great challenge remains to continuously improve sensitivity of protein microarrays for broad applications. A copolymer brush is in situ synthesized on both substrate and silica nanoparticle (SNP) surface to efficiently immobilize probe and reporter protein respectively for synergistic amplification of protein microarray signals. As a demonstration, sandwich immunoassay for a cancer biomarker carcinoembryonic antigen (CEA) detection is performed on microarray platform, showing a limit of detection (LOD) of 10pg/ml and dynamic range of 10pg/ml to 100ng/ml. Two orders improvement of LOD is achieved in comparison to the small crosslinker-activated substrate. The improved sensitivity is attributed to not only the high immobilization amount of both probe and reporter but also the favorite protein binding orientations offered by the flexible brushes. This work provides a universal approach to inexpensively and significantly improve protein microarray sensitivity.
Keywords: Silica nanoparticle; Copolymer brush; Protein microarray; Signal amplification
The aggregation of Tyr-Phe dipeptide and Val-Tyr-Val tripeptide in aqueous solution and in the presence of SDS and PEO–PPO–PEO triblock copolymer: Fluorescence spectroscopic studies
by Jilly James; Asit Baran Mandal (pp. 600-605).
The aggregation properties of Tyr-Phe dipeptide and Val-Tyr-Val tripeptide were determined in aqueous solution. Plot of ln(I o/ I) vs [ Q] at 25°C for [peptide-water] systems.λ ex=274nm andλ em=305nm.Display Omitted► For the first time demonstrated that dipeptide and tripeptide form micelles. ► Interactions of these peptides with SDS and PEO–PPO–PEO copolymer were studied. ► Aggregation number of the peptide micelles and their mixed systems were determined. ► Accessibility of DPC quencher was found to be more in dipeptide than tripeptide.The micelle formation of Tyr-Phe dipeptide and Val-Tyr-Val tripeptide has been studied for the first time. The aggregation numbers were determined for both the peptides in aqueous solution and in the presence of SDS and PEO–PPO–PEO triblock copolymer additive environments. The results obtained by steady state and time-resolved fluorescence spectroscopic techniques are in good agreement with each other. The higher value of aggregation number confirms the formation of mixed micelles. The fluorescence lifetime of tyrosine in various micellar and mixed micellar systems were also determined. The decreased lifetime values with the quencher suggested the dynamic nature of the quenching process. However, the possibility of static quenching cannot be ruled out. The accessibility of DPC quencher was found to be more in dipeptide than tripeptide.
Keywords: Peptide; Triblock copolymer; Surfactant; Aggregation number; Lifetime; Accessibility; Mixed micelles
Characteristics of aggregation in aqueous solutions of dialkylpyrrolidinium bromides
by M. Tariq; A. Podgoršek; J.L. Ferguson; A. Lopes; M.F. Costa Gomes; A.A.H. Pádua; L.P.N. Rebelo; J.N. Canongia Lopes (pp. 606-616).
The aggregation properties of three dialkylpyrrolidinium bromide ionic liquids have been studied using different experimental techniques, including isothermal titration calorimetry. On the one hand, this allowed the correlation between the thermodynamics of aggregation and the underlying structural motifs and on the other, the establishment of a bridge between the selfaggregation behaviors of conventional and ionic liquid-based surfactants.Display Omitted► Self-aggregation properties in aqueous solution of pyrrolidinium-based ionic liquids. ► Interfacial tension, fluorescence spectroscopy, NMR, diffusion coefficients of ionic liquids in water. ► Enthalpy of micellization determined by isothermal titration calorimetry. ► Relationship between surfactant structure and thermodynamics of aggregation revealed.Three pyrrolidinium-based ionic liquids— N-dodecyl- N-methylpyrrolidinium bromide, N-butyl- N-octylpyrrolidinium bromide, and N-butyl- N-dodecylpyrrolodinium bromide—were synthesized and characterized by their decomposition temperatures (T d) measured by thermogravimetric analysis, and by their melting point (T m), glass transition (T g) and crystallization temperatures (T cryst) determined by differential scanning calorimetry. Their self-aggregation properties in aqueous solution were studied and their behavior is compared with that of analogous conventional cationic surfactants, namely tetra-alkylammonium bromide salts. The critical micellar concentration, cmcs were obtained by isothermal titration calorimetry (ITC); which were further validated by measurements of interfacial tension, fluorescence and NMR spectroscopy. Enthalpies of micellization were measured at three different temperatures using ITC. The Taylor dispersion method and DOSY NMR were used to determine diffusion coefficients of the ionic liquid surfactants in aqueous solution at 298.15K. Several correlations between structural features of the surfactant species, such as the number and size of their alkyl chains, and the thermodynamic quantities of micellization—expressed by experimental values of cmc, counter-ion binding fraction,ΔmicG∘,ΔmicH∘, andΔmicS∘—are established. We could interpret the different contributions of the two alkyl side chains to the aggregation properties in terms of the balance of interactions in homogeneous and micellar phases, contributing to understanding the aggregation behavior of ionic liquids in water and the parallel between these systems and traditional ionic surfactants.
Keywords: Ionic liquids; Water; Self-aggregation; Critical micelle concentration; Enthalpy of micellization
Comparison of positional surfactant isomers for displacement of rubisco protein from the air–water interface
by Lizhong He; Sagheer A. Onaizi; Mirjana Dimitrijev-Dwyer; Andrew S. Malcolm; Hsin-Hui Shen; Chuchuan Dong; Stephen A. Holt; Robert K. Thomas; Anton P.J. Middelberg (pp. 617-622).
Two positional isomers of sodium dodecylbenzenesulfonate (SDOBS) were compared for their interaction with the protein rubisco at the air–water interface by neutron reflection.Display Omitted► Protein rubisco is the most abundant protein in nature. ► Sodium dodecylbenzenesulfonate (SDOBS) is one of the most used commercial surfactants. ► Two positional isomers of SDOBS were compared for their interaction with rubisco. ► Deuterated SDOBS isomers were used to provide contrast in neutron reflection study. ► Rubisco displacement is affected by the position of SDOBS isomerisation.Protein–surfactant interaction, which is a function of the protein and surfactant characteristics, is a common phenomenon in a wide range of industrial applications. In this work, we used rubisco, the most abundant protein in nature, as a model protein and sodium dodecylbenzenesulfonate (SDOBS), one of the most widely used commercial surfactants, with two positional isomers (SDOBS-2 and SDOBS-6), as a model surfactant. We first examined the surface tension and the mechanical properties of interfacial mixed rubisco–SDOBS films adsorbed at the air–water interface. The concentration of rubisco in solution was fixed at 0.1mgmL−1 while the SDOBS concentration varied from 0 to 150μM. Both the surface tension and the mechanical strength of the interfacial film decreased with increasing SDOBS concentration. Overall, the surface tension of a rubisco–SDOBS-6 mixture is lower than that of rubisco–SDOBS-2, while the mechanical strength of both systems is similar. Neutron reflection data suggest that rubisco protein is likely denatured at the interface. The populations of rubisco and SDOBS of the mixed systems at the interface were determined by combining non-deuterated and deuterated SDOBS to provide contrast variation. At a low surfactant concentration, SDOBS-6 has a stronger ability to displace rubisco from the air–water interface than SDOBS-2. However, when surfactant concentration reaches 50μM, SDOBS-2 has a higher population than SDOBS-6, with more rubisco displaced from the interface. The results presented in this work suggest that the extent of protein displacement from the air–water interface, and hence the nature of the protein–surfactant interactions at the interface, are strongly affected by the position of surfactant isomerisation, which might allow the design of formulations for efficient removal of protein stains.
Keywords: Positional isomer; Sodium dodecylbenzenesulfonate; Protein rubisco; Neutron reflection; Deuteration; Interfacial tension; Interfacial elasticity; Surface excess
Surface properties and liquid crystal alignment behavior of poly(2-hydroxyethyl methacrylate) derivatives with alkyl ester side chains
by Eun-Ho Sohn; Sung Hyun Kim; Mongryong Lee; Jong-Chan Lee; Kigook Song (pp. 623-632).
The surface properties of poly(2-hydroxyethyl methacrylate) derivatives with alkyl ester side chains were investigated and correlated with the liquid crystal alignment behavior of the polymer films.Display Omitted► PHEMA derivatives with alkyl ester side chains (PHEMA#C, 9⩽#⩽17), where # is carbon number in alkyl groups, were synthesized. ► PHEMA#Cs with ⩾15 showed ordered bilayer structures with very low surface energies inducing homeotropic LC alignment. ► PHEMA#Cs with ⩽13 have disordered structures and stick-slip behavior was observed on their surfaces.Poly(2-hydroxyethyl methacrylate) derivatives with amphiphilic side chains composed of polar ester and non-polar alkyl groups (PHEMA#C, #=9, 11, 13, 15, and 17), where # is the number of carbon atoms in the alkyl side groups, were synthesized. In this paper, the influence of ester and alkyl groups on the molecular structure and wettability of the polymers were studied through varying # in the alkyl side groups. PHEMA#Cs with relatively longer alkyl side groups (#⩾15) show bilayer lamellar structures with well aligned side chains giving rise to the very low surface energies, calculated from advancing contact angles, in the range of 22.7–22.8mN/m. In contrast, PHEMA#Cs with shorter alkyl side groups with #⩽13 have disordered structures on the polymer surfaces and stick–slip behavior was observed when water was used as the test liquid for the advancing contact angle measurements. Furthermore, the alignment behavior of nematic liquid crystal, 5CB on the PHEMA#C films could be correlated with the molecular structure and wettability of the polymers.
Keywords: Poly(2-hydroxyethyl methacrylate) derivative; Comb-like polymer; Alkyl ester side chain; Surface property; Stick–slip behavior; Liquid crystal alignment
Bile acid alkylamide derivatives as low molecular weight organogelators: Systematic gelation studies and qualitative structural analysis of the systems
by Miika Löfman; Juha Koivukorpi; Virpi Noponen; Hannu Salo; Elina Sievänen (pp. 633-644).
Bile acid aminoalkylamides have tendencies for fiber and colloidal aggregate formation, which in some cases lead to supramolecular gelation of organic solvents.Display Omitted► Bile acid amides screened in 36 solvents for supramolecular gelation. ► Kamlet–Taft parameters can probe solvent–gelator interactions. ► Micrometer-scale colloidal aggregates and fibers present. ► Spherical aggregates found uncommon for bile acid organogels.A series of amino- and hydroxyalkyl amides of bile acids have been synthesized and characterized by Fourier transform infrared spectroscopy (FTIR),1H and13C nuclear magnetic resonance spectroscopy (NMR), as well as electrospray ionization mass spectrometry (ESI-MS) measurements. The ability of the synthesized molecules to promote gel formation was systematically investigated. Out of 396 combinations formed by 11 compounds and 36 different solvents, 22 gel-containing systems were obtained with 1% (w/v) gelator concentration. Apart from one exception, the gelator compounds were lithocholic acid derivatives. This challenges the general trend of bile acid–based physical gelators, according to which the gelation ability of lithocholic acid derivatives is poor. A correlation between the values of Kamlet–Taft parameters and solvent preferences for gelators was observed. The morphologies of the solid and gel structures studied with scanning electron microscopy (SEM) showed variability from fibers to spherical microscale aggregates, the latter of which are unique among bile acid–based organogels. The gels exhibited more complex behavior than was previously established with bile acid derivatives, judging by the microscale diversity present in gelating and non-gelating systems and the tendency for polymorphism. This study underlines the importance of both the molecular and colloidal scale aspects of the gelation phenomenon.
Keywords: Bile acid alkylamide; Gel formation; Organogel; SEM; Gel morphology
Synthesis and foaming properties of new anionic surfactants based on a renewable building block: Sodium dodecyl isosorbide sulfates
by Aurélie Lavergne; Ying Zhu; Aldo Pizzino; Valérie Molinier; Jean-Marie Aubry (pp. 645-653).
Foaming Properties of sodium 5-O-dodecyl isosorbide sulfate evaluated during Bikerman’s test.Display Omitted► Synthesis of two anionic (sulfate) surfactants containing an isosorbide moiety as bio-sourced alternatives to the alkyl ether sulfates. ► Comparison of Krafft temperatures and critical micellar concentrations with pure SDS and LES also synthesized in this work. ► Very different aqueous properties of the two isomeric isosorbide surfactants: conformational effects imposed by the isosorbide moiety. ► 5-O-dodecyl isosorbide sulfate: most soluble and most efficient surfactant. Three-times lower cmc than SDS with comparable foaming properties.Two agro-based anionic surfactants containing an isosorbide moiety have been synthesized and their amphiphilic properties evaluated. Since isosorbide is now considered as an important platform chemical of the starch industry, these compounds could represent bio-sourced alternatives to the alkyl ether sulfates (notably lauryl ether sulfate, LES) that are based on petroleum-derived ethylene oxides. As isosorbide is an asymmetric diol, two isomers can be prepared (2- O-dodecyl isosorbide sulfate and 5- O-dodecyl isosorbide sulfate) that show significantly different aqueous properties as regards to their Krafft temperatures and critical micellar concentrations. 5- O-dodecyl isosorbide sulfate is the most soluble and the most efficient surfactant. It possesses a much lower critical micelle concentration (cmc) than sodium dodecyl sulfate, SDS, leading to comparable foaming properties with a three times lower concentration. Its behavior compares well with the one of pure diethoxylated dodecyl sulfate that has also been prepared and evaluated in this work.
Keywords: Isosorbide; Sorbitol; Sodium dodecyl sulfate; Lauryl ether sulfate; Anionic surfactant; Critical micelle concentration; Krafft temperature; Foam stability
Savinase proteolysis of insulin Langmuir monolayers studied by surface pressure and surface potential measurements accompanied by atomic force microscopy (AFM) imaging
by K. Balashev; Tz. Ivanova; K. Mircheva; I. Panaiotov (pp. 654-661).
The AFM images of insulin LB films before the enzyme action and at the end of proteolysis. Kinetic model of peptidase action at air–water interface.Display Omitted► The enzymatic action of Savinase on an insulin monolayer at the air–water interface was studied. ► We applied classical surface pressure and surface potential measurements and AFM imaging. ► We measured simultaneously changes of the surface area and the surface potential versus time. ► An appropriate kinetic model was applied, and the global kinetic constant was obtained. ► The AFM images revealed the state of the insulin monolayers before and after the Savinase action.The mechanism of the enzymatic action of Savinase on an insulin substrate organized in a monolayer at the air–water interface was studied. We followed two steps experimental approach classical surface pressure and surface potential measurements in combination with atomic force microscopy imaging. Utilizing the barostat surface balance, the hydrolysis kinetic was followed by measuring simultaneously the decrease in the surface area and the change of the surface potential versus time. The decrease in the surface area is a result of the random scission of the peptide bonds of polypeptide chain, progressively appearance of amino acid residues, and their solubilization in the aqueous subphase. The interpretation of the surface potential data was based on the contribution of the dipole moments of the intact and broken peptide groups which remain at the interface during the proteolysis. An appropriate kinetic model for the Savinase action was applied, and the global kinetic constant was obtained. The application of the AFM revealed the state of the insulin monolayers before and after the Savinase action. The comparison of the topography of the films and the roughness analysis showed that insulin Langmuir–Blodgett (LB) films transferred before the enzyme action were flat, while at the end of hydrolysis, roughness of films has increased and the appearance of 3D structures was observed.
Keywords: Insulin monolayers; Savinase; Enzyme hydrolysis; Atomic force microscopy (AFM)
On the predictions and limitations of the Becker–Döring model for reaction kinetics in micellar surfactant solutions
by I.M. Griffiths; C.D. Bain; C.J.W. Breward; D.M. Colegate; P.D. Howell; S.L. Waters (pp. 662-671).
A typical surfactant distribution during re-equilibration.Display Omitted► Micellar reaction kinetics may be described by the Becker–Döring equations. ► This system information may be captured by a simplified continuum model. ► A micellar solution following dilution re-equilibrates over two distinct timescales. ► The continuum model agrees with experimental observations for this process. ► Re-equilibration occurs much faster in some cases exposing an alternative mechanism.We investigate the breakdown of a system of micellar aggregates in a surfactant solution following an order-one dilution. We derive a mathematical model based on the Becker–Döring system of equations, using realistic expressions for the reaction constants fit to results from Molecular Dynamics simulations. We exploit the largeness of typical aggregation numbers to derive a continuum model, substituting a large system of ordinary differential equations for a partial differential equation in two independent variables: time and aggregate size. Numerical solutions demonstrate that re-equilibration occurs in two distinct stages over well-separated timescales, in agreement with experiment and with previous theories. We conclude by exposing a limitation in the Becker–Döring theory for re-equilibration of surfactant solutions.
Keywords: Surfactant; Micellization; Aggregation kinetics
Comparative studies on brij reverse micelles prepared in benzene/surfactant/ethylammonium nitrate systems: Effect of head group size and polarity of the hydrocarbon chain
by Sumit Ghosh (pp. 672-680).
Polar head group bulk and polarity of the hydrocarbon chain are important parameters in determining size of reverse micelles. The size decreases with decreasing head group bulk and with increasing the polarity of hydrocarbon chain.Display Omitted► Reverse micellar systems of brij-52, brij-56, briji-58, and brij-93 are investigated. ► The size of the reverse micelles decreases along the series: brij-58>brij-56>brij-52. ► Polarity of micellar core was enhanced with decrease in polar head group bulk.Nonaqueous reverse micelles of brij surfactants are prepared in benzene and ethylammonium nitrate (EAN). The effect of polar head group bulk on reverse micellar size was studied with brij-52, brij-56 and brij-58 whereas the effect of polarity of hydrocarbon chain was investigated taking brij-52 and brij-93 with varyingW s (W s=[EAN]/[surfactant]). Dynamic light scattering (DLS) has been employed to reveal the size and shape of the reverse micelles. Micropolarities of these reverse micelles were investigated by visible spectroscopy using methylene blue (MB) and methyl orange (MO) as molecular optical probes. It has been revealed from the experimental results that with increase in polar head group size reverse micellar size increases. Moreover, it is also observed that with increasing polarity of the hydrocarbon chain the average size of the reverse micelles decreases. It can be concluded that polar head group size and polarity of hydrocarbon chain play important roles in determining reverse micellar size of the brij surfactants apart from theW s ratio, nature of the solvent medium, and concentration of the surfactants.
Keywords: Ionic liquid; Reverse micelles; Non-ionic surfactants; Dynamic light scattering; Visible spectroscopyAbbreviations; EAN; ethylammonium nitrate; DLS; dynamic light scattering; MB; methylene blue; MO; methyl orange
The influence of plant stanol on phospholipids monolayers – The effect of phospholipid structure
by Katarzyna Hąc-Wydro; Anna Zając; Patrycja Dynarowicz-Łątka (pp. 681-689).
■■■Display Omitted► Miscibility and interactions of plant stanol with phospholipids. ► Thermodynamically favorable effect of stanol on PC, contrary to PE and PS films. ► Phase separation in DPPS/stanol mixture. ► Similar effect of stanol and corresponding sterol on the respective phospholipids.This work is aimed at investigating the influence of a plant stanol (β-sitostanol) on Langmuir monolayers from various phospholipids and comparing the effect of phytostanol versus its unsaturated analog – phytosterol (β-sitosterol). The studied phospholipids differed in the structure of polar head (phosphatidylcholine – PC, phosphatidylethanolamine – PE, phosphatidylserine – PS) as well as in the number of monounsaturated chains in PC molecule. It was found that the introduction of stanol into PC monolayers is thermodynamically favorable, contrary to its effect on PE and PS films. The magnitude of condensing and ordering effect of stanol depends both on the number of monounsaturated chains in PC molecule and on the composition of stanol-PC mixture. The analysis of BAM images evidenced phase separation of immiscible components in stanol/DPPS systems. The results of Langmuir monolayer studies for stanol/phospholipids mixtures compared with those for corresponding sterol/phospholipids systems proved quite a similar effect of both compounds on the investigated phospholipid monolayers, despite differences in the structure of tetracyclic ring skeleton.
Keywords: Plant sterol and stanol; Phospholipids; Langmuir films; Brewster angle microscopy
Synthesis and characterization of chiral compounds containing cationic groups as chiral dopants in liquid crystals
by Kongliang Xie; Chunxiang Zhang; Yanhong Yu (pp. 690-694).
Novel chiral molecules containing cationic groups were synthesized. They had good optical activity and could convert nematic liquid crystals to cholesteric liquid crystals.Display Omitted► We designed and synthesized two novel chiral molecules containing cationic groups as functional surfactants for host liquid crystals (LCs). ► The novel chiral molecules containing cationic groups had good optical activity. ► Cationic polar groups did not affect optical rotation direction, but could influence the molar rotation of chiral compounds. ► These chiral molecules could convert nematic phase liquid crystals to cholesteric phase liquid crystals.Novel chiral molecules containing cationic groups, (N-[4-triethylammoniomethyl]-benzoyl ester)-ethyl lactate chloride and bi-(N-[4-triethylammoniomethyl]-benzoyl ester)-isosorbide chloride, were designed and synthesized. Chemical structures of the molecules were characterized by elemental analysis, FT-IR, and1H NMR. The photochemical properties of the chiral compounds and their textures in nematic liquid crystals (LCs) were investigated by optical rotation, circular dichroism (CD), and polarizing optical microscopy (POM). The novel chiral molecules exhibited good optical activity. The chiral compound based on al-ethyl lactate chiral center had a left-handed configuration. The chiral compound based on an isosorbide chiral center had a right-handed configuration. The cationic polar groups did not affect the direction of optical rotation, but could effluence the molar rotation of chiral compounds. The mixtures with dopants showed oily streak textures. Doping of a nematic phase liquid crystal with the chiral molecules converted it to the cholesteric phase.
Keywords: Keyword; Chiral dopant; Liquid crystal; Optical rotation; Texture; Chirality; Circular dichroism
Sorption of nickel and cobalt ions onto cobalt and nickel ferrites
by B. Martin Cabañas; S. Leclercq; P. Barboux; M. Fédoroff; G. Lefèvre (pp. 695-700).
Effect of nickel concentration (0–10mM) on zeta potential of cobalt ferrites particles.Display Omitted► Nickel ferrite and cobalt ferrite have been used as model corrosion products. ► Cobalt and nickel ions sorbed onto ferrites in alkaline pH range. ► Zeta potential of ferrites particles increases in the presence of ions. ► 2-pK/BSM model have been used to determine complexation constants.The corrosion of the metal parts in the primary circuit of pressurized water reactors leads to the release of colloidal particles (NiFe2O4, CoFe2O4, NiO, Ni…) and ionic species (Co, Ni, Cr…). Particles can interact with ionic species in the primary medium, contributing to their transport and to their deposition onto surfaces outside the neutron flux generating radioactive contamination. Sorption and zetametry experiments at 25°C were performed on the Ni2+/CoFe2O4 and Co2+/NiFe2O4 systems in order to determine the behaviour of corrosion products in the fluid of the primary circuit. Sorption appears as surface complexation starting from pH 6 and is followed by precipitation of hydroxide above pH 7.5. Complexation and solubility constants were obtained from the modelling of sorption curves. The two oxide systems present a very similar sorption behaviour, but some differences, due to their different isoelectric points, could be observed on zetametric measurements.
Keywords: Sorption; Zetametry; Nickel; Cobalt; Ferrite; Primary circuit; Modelling; Precipitation; Surface complexation
Molecular dynamics simulations of the electrical double layer on smectite surfaces contacting concentrated mixed electrolyte (NaCl–CaCl2) solutions
by Ian C. Bourg; Garrison Sposito (pp. 701-715).
MD simulation “snapshot” of a NaCl–CaCl2 brine confined in a 58 Å wide nanopore between smectite clay surfaces.Display Omitted► MD simulations of NaCl–CaCl2 electrolyte solutions on smectite clay surfaces. ► Results confirm the existence of three distinct ion adsorption planes. ► Charge inversion occurs in the diffusion ion swarm. ► CaCl+ ion pairs have a high affinity for the clay surface. ► Water and ions diffuse relatively rapidly even near the clay surface.We report new molecular dynamics results elucidating the structure of the electrical double layer (EDL) on smectite surfaces contacting mixed NaCl–CaCl2 electrolyte solutions in the range of concentrations relevant to pore waters in geologic repositories for CO2 or high-level radioactive waste (0.34–1.83molcdm−3). Our results confirm the existence of three distinct ion adsorption planes (0-, β-, and d-planes), often assumed in EDL models, but with two important qualifications: (1) the location of the β- and d-planes are independent of ionic strength or ion type and (2) “indifferent electrolyte” ions can occupy all three planes. Charge inversion occurred in the diffuse ion swarm because of the affinity of the clay surface for CaCl+ ion pairs. Therefore, at concentrations ⩾0.34molcdm−3, properties arising from long-range electrostatics at interfaces (electrophoresis, electro-osmosis, co-ion exclusion, colloidal aggregation) will not be correctly predicted by most EDL models. Co-ion exclusion, typically neglected by surface speciation models, balanced a large part of the clay mineral structural charge in the more concentrated solutions. Water molecules and ions diffused relatively rapidly even in the first statistical water monolayer, contradicting reports of rigid “ice-like” structures for water on clay mineral surfaces.
Keywords: Clay mineral; Smectite; Montmorillonite; Adsorption; Electrical double layer; Triple layer model; Surface complexation model; Surface complex; Diffusion; Molecular dynamics simulation
Cu(II) adsorption by halloysites intercalated with sodium acetate
by Senia Mellouk; Ahmed Belhakem; Kheira Marouf-Khelifa; Jacques Schott; Amine Khelifa (pp. 716-724).
The affinity of the sodium acetate-intercalated halloysites towards copper(II) follows the sequence: unmodified halloysite3COONa into halloysite significantly affects the Cu(II) adsorption. The magnitude in enhancement of copper adsorption on solid phase thus depends on the content of the carboxylic functional groups, which increases with the insertion of CH3COONa into the halloysitic matrix. The involved mechanism is quite complex. It implies electrostatic considerations and a cationic exchange process. The most intercalated sample was found to be very effective as adsorbent of copper(II) from aqueous solutions.
Keywords: Halloysite; Characterisation; Intercalation; Sodium acetate; Adsorption; Copper
Comparative study on composition, structure, and adsorption behavior of activated carbons derived from different synthetic waste polymers
by Fei Lian; Baoshan Xing; Lingyan Zhu (pp. 725-730).
Scanning electron micrographs of activated carbons derived from waste tire rubber (a), polyvinyl chloride (b), and polyethyleneterephtalate (c), respectively.Display Omitted► Polymer waste can be converted into activated carbon with high surface area. ► Aromatic polymers are better precursors for activated carbon than aliphatics. ► Heterogeneous composition and ash content of raw polymers suppress the porosity of activated carbon. ► Polymer-based activated carbons exhibit potential for environmental remediation and cleanup.The composition, structure, and adsorption behavior of activated carbons (ACs) derived from three different types of waste polymers, i.e., tire rubber (TR), polyvinyl chloride (PVC), and polyethyleneterephtalate (PET), by KOH activation were compared. The AC derived from PET exhibited the largest surface area (2831m2/g) and pore volume (1.68cm3/g) due to the homogenous aromatic composition of PET. The AC derived from PVC exhibited relatively lower surface area (2666m2/g) but more narrowed pore size distribution (2–3nm). The complex composition and high ash content of tire particles resulted in AC product with significantly lower surface area (398.5m2/g) and heterogeneous pore width. Adsorption data of methylene blue (MB) were fitted well by Langmuir equation, indicating monolayer coverage on the ACs. The high oxygen content of PET-derived AC heavily affected its adsorption to MB and iodine. Due to the remarkable surface area and highly mesoporous structures, ACs based on both PET and PVC exhibited much higher adsorption capacities than that of TR and commercial coal-based AC (F400). This study demonstrates that the properties of ACs are highly dependent on their starting polymers and the potential of converting synthetic polymer waste into effective adsorbents for environmental remediation and cleanup.
Keywords: Polymer waste; Activated carbon; Characterization; Methylene blue; Adsorption
Synthesis of Fe3O4@poly(methylmethacrylate-co-divinylbenzene) magnetic porous microspheres and their application in the separation of phenol from aqueous solutions
by Yulei Tai; Li Wang; Jingmin Gao; Wael A. Amer; Wenbing Ding; Haojie Yu (pp. 731-738).
The manuscript focused on high efficiency for the separation of phenol from aqueous solutions by magnetic porous microspheres that are prepared by modified suspension polymerization.Display Omitted► Fe3O4@oleic acid nanoparticles as magnetic core. ► Porous poly (methylmethacrylate- co-divinylbenzene) as polymeric shell. ► Magnetic porous microspheres for the remove phenol from aqueous solutions. ► We investigate factors affecting the specific surface area and pore size distribution of magnetic porous microspheres. ► Increasing specific surface area and polarity of magnetic porous microspheres will increase the adsorption efficiency.A simple strategy to fabricate magnetic porous microspheres of Fe3O4@poly(methylmethacrylate- co-divinylbenzene) was demonstrated. The magnetic microspheres, consisting of polymer-coated iron oxide nanoparticles, were synthesized by the modified suspension polymerization of methacrylate and divinylbenzene in the presence of a magnetic fluid. The morphology and the properties of the magnetic porous microspheres were examined by scanning electron microscopy, transmission electron microscopy, superconducting quantum interference device, Fourier transform infrared spectroscopy, thermogravimetry, and X-ray powder diffraction. The pore size distribution and the specific surface area of the microspheres were measured by nitrogen sorption and mercury porosimetry technique. As predicted from the previous knowledge, the magnetic porous microspheres possessed a high specific surface area using n-hexane as a porogen. It was further found that the amounts of divinylbenzene and methacrylate, the ratio of porogens, and the dosage of ferrofluids affect the specific surface area of the microspheres. Furthermore, the microspheres were applied to remove phenol from aqueous solutions. The results showed that the microspheres had a high adsorption capacity for phenol and a high separation efficiency due to their porous structure, polar groups, and superparamagnetic characteristic.
Keywords: Magnetic properties; Porous microspheres; Phenol; Adsorption
Changes in induced polarization associated with the sorption of sodium, lead, and zinc on silica sands
by P. Vaudelet; A. Revil; M. Schmutz; M. Franceschi; P. Bégassat (pp. 739-752).
Phase lag between the current and the voltage for different types of cations sorbed onto silica.Display Omitted► Induced polarization is sensitive to sorption of metallic cations on silica. ► The main polarization mechanism is related to the polarization of the Stern layer. ► A Stern layer polarization model coupled with a complexation model can explain the induced polarization data.Low-frequency dielectric spectroscopy can be measured in terms of a conductance and a phase lag between the electrical current and the electrical field. This conductance and phase lag can be written as into a complex conductivity with both an in-phase and quadrature components that are frequency dependent. In sands, the low-frequency (10mHz–40kHz) spectra of the complex conductivity are dominated by the polarization of the electrical double layer (especially the internal part of the electrical double layer called the Stern layer) and the Maxwell–Wagner polarization (typically above 100Hz). We present a polarization that is able to explain the complex conductivity spectra including the grain size distribution, the porosity, and the complexation of the mineral surface with the ions of the pore water. To test this model, we investigate the sorption of various cations (Na, Pb, Zn) characterized by different affinities with the surface of silica. Sand column experiments were carried out to see the change in the complex conductivity during the advective/dispersive transport of a lead nitrate solution and a zinc sulfate solution, replacing a sodium chloride solution in the pore space of the sand. The complex conductivity model is able to explain the change of the phase over time.
Keywords: Low-frequency dielectric spectroscopy; Induced polarization; Surface conductivity; Silica; Sand; Electrical double layer; Zinc; Lead; TLM
Adsorption and solvent desorption behavior of ion-exchanged modified Y zeolites for sulfur removal and for fuel cell applications
by Ligang Lin; Yuzhong Zhang; Hongyu Zhang; Fuwei Lu (pp. 753-759).
Concentration profile of washing solvent during desorption: most sulfur compounds were recovered during initial stage. Desorption behavior of various zeolites was markedly related with their binding force and sulfur.Display Omitted► Adsorption/desorption behavior is markedly related with binding force. ► Most sulfur is recovered at initial stage during on site solvent washing. ► Outlet sulfur concentration cannot reach the corresponding initial sulfur level. ► Preferential adsorption of thiophenic sulfur exists in zeolites.Typical ion-exchanged modified Y zeolites (AgY and CeY) were prepared for sulfur removal. The adsorption and desorption behavior of typical sulfur and hydrocarbon molecules in various Y zeolites has been investigated by the adsorption breakthrough and on site solvent washing experiments, as well as computer simulation. Breakthrough experiments showed that the adsorption capacity for thiophenic sulfur increased for the studied adsorbents as follows: CeY>AgY>NaY. The higher initial sulfur concentration accelerated the appearance of breakthrough, and the outlet sulfur concentration, in all cases, cannot reach the corresponding initial sulfur level. The concentration profile of washing solvent during desorption process showed that most of the sulfur compounds could be recovered at initial desorption stage. The desorption rates of typical Y zeolites follow the order: NaY>AgY>CeY, which is the reverse as that found in adsorption capacity. The distinct adsorption and desorption behavior of CeY, AgY, and NaY zeolites was markedly related with their various binding force (S–M coordination, π-complexation, and Van der Waals force) with sulfur compounds. The adsorption isotherms and density distribution snapshots study by computer simulation confirmed the preferential adsorption of thiophenic sulfur.
Keywords: Zeolite; Solvent desorption; Adsorption; Thiophene; Desulfurization
Kinetics and thermodynamic study of aniline adsorption by multi-walled carbon nanotubes from aqueous solution
by Hind Al-Johani; Mohamed Abdel Salam (pp. 760-767).
This graph shows the Arrhenius plot of the pseudo second-order kinetics for the adsorption of aniline on different MWCNTs.Display Omitted► Multi-walled carbon nanotubes (MWCNTs) were used for the adsorptive removal of aniline. ► Adsorption was dependent on MWCNTs dosage, contact time, aniline concentration, and solution pH and temperature. ► Kinetic study revealed that the adsorption followed the pseudo-second order. ► Adsorption of aniline occurs in two consecutive steps including slow intra-particle diffusion through the nanotubes. ► Thermodynamic studies indicated the spontaneity and exothermic nature of the adsorption.Multi-walled carbon nanotubes (MWCNTs) were used in the adsorptive removal of aniline, an organic pollutant, from an aqueous solution. It was found that carbon nanotubes with a higher specific surface area adsorbed and removed more aniline from an aqueous solution. The adsorption was dependent on factors, such as MWCNTs dosage, contact time, aniline concentration, solution pH and temperature. The adsorption study was analyzed kinetically, and the results revealed that the adsorption followed pseudo-second order kinetics with good correlation coefficients. In addition, it was found that the adsorption of aniline occurred in two consecutive steps, including the slow intra-particle diffusion of aniline molecules through the nanotubes. Various thermodynamic parameters, including the Gibbs free energy change (Δ G°), enthalpy change (Δ H°) and entropy change (Δ S°), were calculated. The results indicated that the spontaneity of the adsorption, exothermic nature of the adsorption and the decrease in the randomness reported as Δ G°, Δ H° and Δ S°, respectively, were all negative.
Keywords: Carbon nanotubes; Aniline; Adsorption; Kinetics; Thermodynamics
Salt precipitation and trapped liquid cavitation in micrometric capillary tubes
by Majda Bouzid; Lionel Mercury; Arnault Lassin; Jean-Michel Matray (pp. 768-776).
The paper describes how secondary precipitates, in an initially-uniform capillary tube, are able to change the local thermo-chemical conditions.Display Omitted► Salt precipitation in initially homogeneous pores changes their topology. ► The “heterogeneized” capillary tube hosts stable and metastable water simultaneously. ► The metastable liquid cavitates after a certain (characteristic) time.Laboratory evidence shows that the occurrence of solid salt in soil pores causes drastic changes in the topology of the porous spaces and possibly also in the properties of the occluded liquid. Observations were made on NaCl precipitation in micrometric cylindrical capillary tubes, filled with a 5.5M NaCl aqueous solution and submitted to drying conditions. Solid plug-shaped NaCl (halite) commonly grows at the two liquid–air interfaces, isolating the inner liquid column. The initially homogeneous porosity of the capillary tube becomes heterogeneous because of these two NaCl plugs, apparently closing the micro-system on itself. After three months, we observed cavitation of a vapor bubble in the liquid behind the NaCl plugs. This event demonstrates that the occluded liquid underwent a metastable superheated state, controlled by the capillary state of thin capillary films persisting around the NaCl precipitates. These observations show, first, that salt precipitation can create a heterogeneous porous medium in an initially regular network, thus changing the transfer properties due to isolating significant micro-volumes of liquid. Second, our experiment illustrates that the secondary salt growth drastically modifies the thermo-chemical properties of the occluded liquid and thus its reactive behavior.
Keywords: Porous network; Unsaturated zone; Capillary geochemistry
Nanotribology of polyvinylidene difluoride (PVDF) in the presence of electric field
by Hyungoo Lee; Bharat Bhushan (pp. 777-784).
The Au (gold) coated poled PVDF films without (top) and with (bottom) lubricant film (65nm) at present of the externally applied electrical field and the AFM tip. In this study, effect of piezoelectricity and lubricant with electric field on tribological properties was investigated,using poled and unpoled PVDF.Display Omitted► Effect of piezoelectricity with electric field was studied. ► Lubricant effect on tribological properties was investigated. ► Scale effect was also studied using an AFM and a tribometer.Polyvinylidene difluoride (PVDF) is one of the most widely used piezoelectric materials in micro-electromechanical systems (MEMS) and nano-electromechanical systems (NEMS) due to its excellent properties. Its applications range from biological to electric devices, such as an artificial hip joint, a microgripper, and a force sensor. It is critical to understand friction, adhesion, and wear mechanisms of this material. In this study, effect of piezoelectricity and lubricant with electric field on tribological properties was investigated, using poled and unpoled PVDF. To understand the tribological properties at nano- and macroscales, scale effect was also studied using an AFM and a tribometer. Relevant mechanisms are discussed.
Keywords: Polyvinylidene fluoride; Atomic force microscopy; Nanotribology; Lubricant; Adhesion; Friction; Wear; MEMS/NEMS
Template-assisted encapsulation of fluorinated silanes in silica films for sustained hydrophobic–oleophobic functionality
by Aaron J. Kessman; Darran R. Cairns (pp. 785-792).
Fluorosilanes usually surface segregate when incorporated into sol–gel films. Surfactant templating aids in encapsulation of fluorosilanes, which form a mesoscopically dispersed functional phase within the silica framework. Template and fluorosilane concentrations concentration may be used to tune film properties to remain non-wetting even after the surface-enriched top layer is worn away.Display Omitted► Surfactant templating of silica films aided in bulk encapsulation of fluorosilanes, which are usually surface-enriched. ► Encapsulation increased non-wetting character of film bulk after removal of top surface. ► N2 adsorption porosimetry indicates a co-surfactant effect between surfactant and fluorosilane. ► Encapsulation may be used to tune film properties to remain functional even after the surface-enriched top is worn away.This work explores the use of templated silica films as scaffolds for encapsulating surface-segregating functional organic moieties as a mesoscopically dispersed phase with the goal of imparting sustained functionality. Block copolymer surfactant templated hydrophobic–oleophobic fluorinated silica films were synthesized via sol–gel co-condensation and coated on glass substrates. Fluorosilane and surfactant template concentrations were varied, and coating surface properties measured before and after abrasion of the top surface. Surface physical and chemical properties were investigated using XPS and contact angle measurements. Nitrogen adsorption porosimetry and TEM were used to examine the effect of templating and fluorosilane encapsulation on the surrounding silica framework. The results show that surfactant template concentration may be used to tune the dispersion of the fluorosilane-rich phase within the silica film in order to allow exposed surfaces to maintain much of the original functionality of the pristine top surface.
Keywords: Hydrophobic; Oleophobic; Surfactant templating; Encapsulation; Porosimetry; Coating
Morphological behavior of thin polyhedral oligomeric silsesquioxane films at the molecular scale
by Guennadi Evmenenko; Benjamin Stripe; Pulak Dutta (pp. 793-799).
The morphology of POSS films can be tuned by adjusting different factors on the molecular scale: from monolayer on hydrophilic surfaces, bilayers on hydrophobic surfaces, and uniform thicker films obtained by using a solvent with increased cohesion parameters.Display Omitted► XRR was used to study the structure of thin films of polyhedral oligomeric silsesquioxanes. ► The morphology of POSS films can be tuned by adjusting of different factors on the molecular scale. ► Different types of coatings (monolayer, bilayer or thicker film) are observed. ► The role of conformational and energetic factors is discussed.Synchrotron X-ray reflectivity (XRR) was used to study the structure of thin films of polyhedral oligomeric silsesquioxanes (POSS) with side organic chains of different flexibility and containing terminal epoxy groups. POSS films were deposited from volatile solvents on hydroxylated and hydrogen-passivated silicon surfaces. The XRR data show a variety of structural morphologies, including autophobic molecular monolayers and bilayers as well as uniform films. The role of conformational and energetic factors governing the development of different morphologies in a restricted geometry is discussed.
Keywords: Specular X-ray reflectivity; Polyhedral oligomeric silsesquioxanes; Thin films; Molecular rearrangement
Superviscosity and electroviscous effects at an electrode/aqueous electrolyte interface: An atomic force microscope study
by Svetlana Guriyanova; Victor G. Mairanovsky; Elmar Bonaccurso (pp. 800-804).
Is the interfacial viscosity of nanoconfined aqueous solutions also influenced by an applied electric field, and if yes to what extent?Display Omitted► We modified an atomic force microscope (AFM) for controlling the electric potential of a flat sample and a tip in an electrolyte. ► and for measuring the interaction force between sample and tip down to nanometer separations. ► We found the effective dynamic viscosity close to surface and tip increasing by orders of magnitude with respect to bulk. ► and the effective viscosity at the interface being controlled by the applied electric potential.Several authors observed in the past a larger than twofold increase in viscosity of organic liquids under the influence of an electric field of the order of 106V/m. This was called electro viscous effect (EVE). Significantly higher electric fields, of up to 108–109V/m, arise in the electric double layer in solutions close to an electrode. Therefore, the viscosity can be expected to increase at strongly charged liquid–solid interfaces. In more recent years, it was also observed that even in the absence of an externally controlled electric field the viscosity of water can be up to 107 times higher close to a hydrophilic surface than in the bulk (“hydrophilic forces”). Here, we present electrochemical atomic force microscopy (EC-AFM) measurements by which we can overcome the critical threshold of the electric field H=106V/m by the control of the potentials applied to both a conducting sample and a conducting tip immersed in solution. Using the EC-AFM, we have investigated for the first time the EVE in an aqueous electrolyte. We can show that by controlling the applied potential, we can control the viscosity and the thickness of the super viscous liquid layer close to the solid interface. Using this technique, we are further able to separate effects on viscosity induced by the hydrophilicity of the surfaces, by the strong nanoconfinement of the liquid between tip and surface, and by the applied electric field.
Keywords: Atomic force microscopy; Superviscosity; Aqueous electrolyte solution; Electroviscous effect; Nanoconfinement; Electric field strength
Influence of a nanorod molecular layer on the biological activity of neuronal cells. A semiclassical model for complex solid/liquid interfaces with carbon nanotubes
by Stefano A. Mezzasalma (pp. 805-817).
Scheme of a neuron network (in gray) interfaced to a carbon nanotube film (in blue, around a cell soma).Display Omitted► Neuronal cells/membranes modeled as stastistical devices governed by semiclassical/quantum-like mechanisms. ► Spectroscopic interpretation for the frequency change of a biological signal, here elicited by a power broadening effect of the carbon phase. ► Four biological enhancement agents (synaptic strength, electrochemical coupling, geometric/electric connectivity, electromagnetic/polarization effects).A general account of electric effects is given for a biological phase interacting with a nanorod molecular layer by means of the formed hard–soft and solid–liquid interfaces. In particular, the frequency enhancement previously detected for the spontaneous activity of neuronal cultures interfaced with carbon nanotubes is quantitatively explained upon a quantum/semiclassical description, where the duration of a biological signal is viewed as the (average) lifetime of a decaying state (or population of states), and the effect of the carbon phase as a linewidth broadening. Four contributions were principally accounted for, one biological, for the synaptic strength, one electrochemical, for the overall capacitance increase implied by the nanotube double layers, one geometric, for the typical scales ruling the electron and ion conduction mechanisms, and one electromagnetic-like, translating the membrane polarization changes. These calculations predict an enhancement factor equal on average to ≃6.39, against a former experimental value ≃6.08.
Keywords: Nanorod thin film; Neuronal electric properties; Carbon nanotube; Electrochemical double layer; Electromagnetic enhancement; Network geometry
Fourier Transform Rheology as a universal non-linear mechanical characterization of droplet size and interfacial tension of dilute monodisperse emulsions
by Kathrin Reinheimer; Massimiliano Grosso; Manfred Wilhelm (pp. 818-825).
FT-Rheology as a novel procedure to determine emulsion properties like droplet size or interfacial tension based on the simulation of a universal curve for emulsions via ellipsoidal models.Display Omitted► FT-Rheology characterizes emulsions under nonlinear oscillatory shear. ► Simulation of dilute monodisperse emulsions with variable properties under LAOS. ► Maffettone Minale model with Batchelor theory calculate interfacial shear stress. ► Development of a universal emulsion curve E for characterizing emulsion properties. ► Determined droplet size via E comparable to result obtained via Palierne model.A new protocol to gain interfacial tension and droplet size of dilute monodisperse emulsions from Fourier Transform Rheology (FTR), is proposed. Specifically, a universal dimensionless quantity E was found at small strain amplitudes to correlate with the droplet size of the emulsion where E is inversely related to the square of the capillary number Ca and directly proportional to the relative intensities of the fifth and third harmonics, I5/ I3. The limiting value E0 at small strain deformations can be used as a universal parameter to calculate different emulsion properties. Different morphological constitutive models for emulsions were used to establish the universality of the parameter E0. Preliminary analysis on experimental data confirms the validity of this approach for the characterization of emulsion properties, including the estimation of interfacial tension and droplet radius.
Keywords: Fourier Transform Rheology; Emulsion; Ellipsoidal model; Droplet size; Interfacial tension
High spatial resolution label-free detection of antigen–antibody binding on patterned surface by imaging ellipsometry
by Meng-Jie Chang; Chao-Ran Pang; Jun Liu; Hua Bai; Jun Deng; Zhu-Guo Xu; Hao-Li Zhang (pp. 826-833).
Quantitatively study of the antibody/antigen interaction in surface area down to 32×32μm2 has been successfully achieved by high spatial resolution imaging ellipsometry.Display Omitted► Large area protein micro-arrays with feature size down to 8 × 8 μm2 square spots could be clearly imaged by imaging ellipsometry. ► By using different patterns, 100-1600 label-free protein spots were imaged simultaneously. ► The thickness changes during the formation of protein patterns were quantitatively monitored on the 32 × 32 μm2 square spots. ► Quantitatively ellipsometric measurements were performed on protein arrays with densities above 5 × 104 spot/cm2. ► A single spot detection limit as low as 1.2 pg/spot was achieved.High spatial resolution and large area thickness mapping of label-free protein microarray has been achieved using imaging ellipsometry (IE) under optimized conditions. The protein patterns with feature size down to 8×8μm2 was readily imaged, and the binding between the surface immobilized antigen and the antibody was monitored. Quantitative thickness analysis of antibody–antigen binding on the 32×32μm2 micron spots was successfully performed, and we have obtained a limit of detection as low as 1.2pg/spot. This work demonstrates that appropriately optimized IE could be used as a highly sensitive and high through-put label-free technique for studying surface antigen–antibody recognition in sub-40μm scale.
Keywords: Label-free; Imaging ellipsometry; High spatial resolution; Microcontact printing; Detection limit