Journal of Colloid And Interface Science (v.349, #1)
A systematic study of equilibrium structure, thermodynamics, and rheology of aqueous CTAB/NaNO3 wormlike micelles
by Matthew E. Helgeson; Travis K. Hodgdon; Eric W. Kaler; Norman J. Wagner (pp. 1-12).
Dilution viscometry of wormlike micelles from the entangled to dilute regimes. Combined with SANS and calorimetry,these measurements yield structure–property relationships for self-assembled micellar solutions.We present a systematic study of the self-assembly of wormlike micelles (WLMs) comprised of cetyltrimethylammonium bromide (CTAB) and sodium nitrate (NaNO3) in aqueous solution as a function of CTAB concentration, NaNO3 concentration, and temperature throughout the dilute and semi-dilute regions of the phase diagram where linear micelles are observed. Combining measurements using isothermal titration calorimetry, rheometry, flow-birefringence, cryo-transmission electron microscopy (cryo-TEM), and small angle neutron scattering (SANS) enables complete characterization of the structure, thermodynamics, and rheology of CTAB/NaNO3 micelles. The addition of NaNO3 is found to increase the micellization enthalpy as well as the micellar scission energy, resulting in the elongation and growth of WLMs. We find quantitative agreement between the scission energy determined from rheology and the enthalpy of micellization determined from ITC, as well as for contour lengths extracted from rheology and SANS. At fixed molar ratio of NaNO3 and CTAB, the solution rheology exhibits scaling consistent with dilute, semi-dilute overlapping, and semi-dilute entangled regimes typically found in polymer solutions, as confirmed by cryo-TEM and SANS. The transition between these scaling regimes coincides with the structural transitions identified by SANS. The results validate the relationship between structural parameters and rheological behavior underlying theories for ionic WLMs.
Keywords: Wormlike micelles; SANS; Viscoelasticity; Entanglement
Bioengineering of stainless steel surface by covalent immobilization of enzymes. Physical characterization and interfacial enzymatic activity
by Anne Caro; Vincent Humblot; Christophe Méthivier; Michel Minier; Lucica Barbes; Joachim Li; Michèle Salmain; Claire-Marie Pradier (pp. 13-18).
The enzymes lysozyme and trypsin were chemisorbed to stainless steel by a wet chemical process so as to design active surfaces against biofilms.Two hydrolytic enzymes, namely lysozyme and trypsin, were covalently immobilized onto stainless steel surfaces using wet chemistry processes. The immobilization strategy took advantage of the spontaneous physisorption of the polymer poly(ethylene imine) (PEI) onto stainless steel to yield a firmly attached, thin organic layer containing a high density of primary amine functions. Both enzymes were then covalently grafted to the surface via a glutaraldehyde cross-linker. Alternatively, a thicker underlayer of PEI was chemisorbed by cross-linking two PEI layers by glutaraldehyde. The effective presence of both enzymes on the stainless steel surfaces and their relative amount were assessed by immunochemical assays employing specific anti-enzyme antibodies. Eventually, the hydrolytic activity of the immobilized enzymes was evaluated by local enzymatic tests with suitable substrates. This work demonstrates that, although the amount of enzymes did not vary significantly with the underlayer thickness, their hydrolytic activity could be much improved by increasing the distance from the oxide surface and, likely, by favoring their accessibility. Our data suggest that the immobilization of enzymes on solid oxide surfaces is feasible and efficient, and that the enzymes retain catalytic activity. It may thus provide a promising route towards biofilm-resistant materials.
Keywords: Stainless steel; Poly(ethylene imine); Lysozyme; Trypsin; Anti-biofilm surfaces
Controlled fabrication of oriented co-doped ZnO clustered nanoassemblies
by K.C. Barick; M. Aslam; Vinayak P. Dravid; D. Bahadur (pp. 19-26).
The incorporation of dopants/co-dopants into ZnO clustered nanoassemblies could modulate local electronic structure due to formation/activation of defects which significantly alters their structural, vibrational, optical and magnetic properties.Clustered nanoassemblies of Mn doped ZnO and co-doped ZnO (Mn, Sn co-doped ZnO; Mn, Sb co-doped ZnO; and Mn, Bi co-doped ZnO) were prepared by refluxing their respective precursors in diethylene glycol medium. The co-doping elements, Sn, Sb and Bi exist in multi oxidation states by forming Zn–O–M (M=Sb, Bi and Sn) bonds in hexagonal wurtzite nanostructure. The analyses of detailed structural characterization performed by XRD, X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM), show that co-doping ions are successfully incorporated into the ZnO nanostructure and do not appear as precipitates or secondary phases. HRTEM analysis also confirmed the oriented attachment of nanocrystals as well as their defect structures. The formation/activation of higher amount of intrinsic host defects, for instance, oxygen vacancies in co-doped ZnO as compared to Mn doped ZnO sample is evident from Raman spectra. The doped and co-doped samples exhibit ferromagnetic like behavior at room temperature presumably due to the presence of defects. Specifically, it has been observed that the incorporation of dopant and co-dopants into ZnO structure can modulate the local electronic structure due to the formation/activation of defects and hence, cause significant changes in their structural, vibrational, optical and magnetic properties.
Keywords: Nanocrystals; Nanoassemblies; Doped ZnO; Defects; Oriented attachment
Surface chemistry of surfactant AOT-stabilized SnO2 nanoparticles and effect of temperature
by Meitram N. Luwang; Raghumani S. Ningthoujam; Naorem S. Singh; Raghvendra Tewari; Sri K. Srivastava; Rajesh K. Vatsa (pp. 27-33).
Interaction of sulfonate group of the surfactant AOT with SnO2 nanoparticles before and after heat treatment.Display Omitted► Synthesis of SnO2 nanoparticles by AOT/hexane/water microemulsion route. ► Interaction of surfactant AOT with SnO2 nanoparticles. ► New IR peak at 1448cm−1 due toSO42- residue over SnO2. ► SnO2 nanoparticles show green luminescence which is due to oxygen vacancies.SnO2· xH2O nanoparticles were prepared at room temperature by the microemulsion route. Sodium bis(2-ethylhexyl) sulfosuccinate (AOT) was used as a surfactant to stabilize the nanoparticles. These nanoparticles show green luminescence at 510nm, which has been assigned to oxygen vacancies. Infrared spectra of samples heated in the temperature range 500–900°C show bond formation between SnO2 nanoparticles andSO42-, which arises from oxidation ofSO3- present in AOT. This was further supported by X-ray diffraction. Shape transformations of the particles from triangular to spherical and then to rectangular was observed as the heat-treatment temperature was increased, and this is related to the surface energy of particles. An enhancement in emission intensity of Eu3+ was observed when Eu3+ ions were doped into the SnO2 nanoparticles due to significant energy transfer from SnO2 (or Eu–O) to Eu3+ through surface-mediated energy transfer as compared to direct excitation of Eu3+ at 397nm. Interestingly, these nanoparticles are dispersible in water, and can be incorporated into polymer-based materials such as polyvinyl alcohol to give homogeneous films, giving rise to blue and red emissions.
Keywords: Nanoparticles; Microemulsion; Green luminescence; Energy transfer
Preparation of Eu3+ doped (Y,Gd)2O3 flowers from (Y,Gd)2(CO3)3·nH2O flowerlike precursors: Microwave hydrothermal synthesis, growth mechanism and luminescence property
by Shen-Hua Dai; Yun-Fei Liu; Yi-Nong Lu (pp. 34-40).
The morphology evolution process of precursors from colloidal spheres ((Y,Gd)(OH)CO3·nH2O) to crystalline flowers ((Y,Gd)2(CO3)3·nH2O) under microwave-hydrothermal condition.In this study, (Y,Gd)2O3 and (Y,Gd)2O3:Eu flowerlike microstructures were prepared through two steps: well-organized 3-dimensional (3D) flowerlike precursors were first synthesized by a facile urea-based microwave hydrothermal method, then followed by heat treatment. The morphology of the 3D flowerlike precursors could be modulated by adjusting the synthetic conditions including concentration of the starting material, reaction time and temperature. Higher the concentration of Y/Gd ions or reaction temperature, earlier the 3D flowerlike precursors were obtained. The samples were characterized by various means. The flowers were found to derive from colloidal spheres, which experienced a dissolution/crystalline, attachment and self-assembly process. Room temperature photoluminescence spectrum of 3D flowerlike (Y,Gd)2O3:Eu showed enhanced emission property than the spheres.
Keywords: (Y,Gd); 2; O; 3; :Eu; Morphology; Microwave hydrothermal; Urea; Photoluminescence
Electrodeposition of latex particles in the presence of surfactant: Investigation of deposit morphology
by C. Pignolet; M. Euvrard; A. Foissy; C. Filiâtre (pp. 41-48).
Kinetics of surface coverage of particles on the electrode observed in CTAB (▪), CTAC (▪), and CTAHS (▪) solutions at concentrations of 5×10−5 M (open) and 5×10−4 M (solid).The deposition of micrometric latex particles on a polarized nickel surface was investigated using a laminar flow cell equipped with a video assembly used to observe and record particle behavior near the electrode. The effects of the nature of the counterions and the concentrations of surfactants on the deposit structure were studied. Negative polystyrene latex particles were turned positive by adsorption of cetyltrimethylammonium in the form of different salts: bromide (CTAB), chloride (CTAC), and hydrogenosulfate (CTAHS). Image analysis was used to gain information on the mechanisms of particle deposition on the electrode. At CTAB concentration 5×10−5M, mostly single particles were deposited on the electrode and their adhesion was irreversible. The adsorption mechanism was shown to be dependent on the succession of electrophoretic migration and attractive particle–surface interactions. At a higher CTAB concentration (5×10−4M) a transient 3D aggregation was observed which was attributed to electroosmotic and electrohydrodynamic phenomena in the vicinity of the electrode. In the presence of CTAC, aggregates were formed on the electrode for both concentrations. In the case of CTAHS the deposition rate was very low in comparison with CTAB and CTAC. This result was explained by the lower zeta potential of the particles with respect to the other cases. The formation of the aggregates was reversible; furthermore, their morphologies were strongly dependent on the kind of counterion. The aggregates formed in CTAB solution were dense while more open structures were observed with CTAC.
Keywords: Colloidal particles; Electrodeposition; Surfactant; Counterions; Adsorption; Image analysis
Iron oxyhydroxide nanostructured in montmorillonite clays: Preparation and characterization
by Juan Carlo Villalba; Vera R.L. Constantino; Fauze Jacó Anaissi (pp. 49-55).
The SEM micrograph of the akaganéite-like materials which were isolated in this work and consist of regular rod-like particles of about 400–500nm aggregated to form clusters.Akaganéite is a very rare iron oxyhydroxide in nature. It can be obtained by many synthetic routes, but thermohydrolysis is the most common method reported in the literature. In this work, akaganéite-like materials were prepared through the thermohydrolysis of FeCl3·6H2O in water and suspensions containing clay minerals. X-ray diffractometry (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) data show that the clays determine the crystal phase and size of the iron oxyhydroxide crystals. According to XRD and FTIR data, β-FeO(OH) (akaganéite) is the main metal oxyhydroxide phase. Considering the small basal spacing ( d001) displacement observed when comparing the XRD patterns of pristine clays with the composites containing β-FeO(OH), the iron oxyhydroxide should be mostly located on the basal and edge surfaces of the clay minerals. UV–Vis electronic absorption spectra indicate that the preferred phase of the iron oxyhydroxide is determined by the nature of the clay minerals.
Keywords: Akaganéite; Clays; Thermohydrolysis
Synthesis and characterization of bioactive hydroxyapatite–calcite nanocomposite for biomedical applications
by G. Suresh Kumar; E.K. Girija; A. Thamizhavel; Y. Yokogawa; S. Narayana Kalkura (pp. 56-62).
Sol–gel synthesis of hydroxyapatite (HA) using citric acid as organic modifier has resulted in the formation of highly bioactive HA–calcite nanocomposite, a superior alternative to HA for biomedical applications when ignored washing process during synthesis.In a number of recent reports on the synthesis of hydroxyapatite (HA) by sol–gel method using citric acid as an organic modifier, washing was an essential step to remove the byproducts and citric acid. In the present study we made an attempt to synthesize HA by sol–gel method in the presence of citric acid, wherein we have employed calcination technique instead of the conventional washing process. The products thus obtained were analyzed by X-ray diffraction (XRD), Fourier Transform-Infrared (FT-IR) spectroscopy, thermogravimetry and scanning electron microscopy which confirmed the formation of a nanocomposite of HA and CaCO3 (calcite) when citric acid was added during synthesis. HA is known to be bioactive and bioresorbable but the rates are too low. On the other hand, CaCO3 is highly biodegradable. The combination of HA and CaCO3 compromised the demerits of each others. The dissolved Ca ions from CaCO3 enhanced the supersaturation of the surrounding fluid which resulted in higher bioactivity of HA.
Keywords: Hydroxyapatite; Nanocomposite; Sol–gel method; Citric acid
Characteristics of polymers that stabilize colloids for the production of graphene from graphene oxide
by Mohsen Moazzami Gudarzi; Farhad Sharif (pp. 63-69).
Stabilization of graphene oxide and graphene dispersion using polymeric stabilizers has been investigated. Only polymers with right specification can be served as stabilizer for graphene.Display Omitted► Polymers can be served as stabilizers for graphene. ► Polymer-graphene affinity is decisive for the formation of protective layer. ► Only polymers with right molecular weights can be employed as stabilizer. ► Molecular weights of polymer stabilizer mostly depends on size of graphene sheets.There is an increasing interest to find cost-effective methods to produce graphene. It is common to produce graphene from the reduction of graphene oxide colloids. The key to this method’s success and producing graphene layers is having stable colloids of graphene and graphene oxide. The objective of this paper is to study the characteristics of a polymeric stabilizing agent that ensures stabilization of both graphene and graphene oxide. After providing a theoretical basis for selecting a proper polymer, experimental evaluations are performed to show that only proper polymers with the right molecular weight can serve as the stabilizing agent for both graphene and graphene oxide.
Keywords: Steric stabilization; Graphene; Graphene oxide; Adsorbtion; Stabilizer
Facile method for preparing organic/inorganic hybrid capsules using amino-functional silane coupling agent in aqueous media
by Fumio Kurayama; Satoru Suzuki; Tetsuro Oyamada; Takeshi Furusawa; Masahide Sato; Noboru Suzuki (pp. 70-76).
Capsules with organic/inorganic hybrid shells can be successfully produced by a reaction between alginate shells and aminopropyltriethoxysilane without any organic solvents, precipitating agents and catalysts.A new and facile method for preparing microcapsules with 3-aminopropyltriethoxysilane (APTES)/alginate hybrid shell (AP-capsule) is proposed based on gelling and sol–gel processes. In this method, conventional capsules with alginate shells (Alg-capsule) are produced by dripping carboxymethyl cellulose solution containing calcium chloride into a sodium alginate solution. Subsequently, addition of the Alg-capsules to an aqueous APTES solution induces the formation of APTES/alginate hybrid shells. The optical observation shows that the texture of AP-capsules is more glossy and transparent than that of Alg-capsules. The surface morphology and elemental composition of microcapsules were characterized by Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). The results suggest that APTES molecules are incorporated to the framework of the alginate shells via electrostatic interaction between amino groups of APTES and carboxyl groups of alginate and the hybrid shells have a dense and homogeneous structure. In the formation reaction, the shrinking of the capsule shells occurs and the accumulation of APTES in the capsule shells proceeds with pseudo first-order kinetics. Moreover, these behaviors are greatly influenced by pH of the reaction solution, especially promoted under acidic and alkaline conditions.
Keywords: Microcapsule; Aminopropyltriethoxysilane; Alginate; Silane coupling agent; Sol–gel
Synthesis, characterisation and antibacterial activity of PVA/TEOS/Ag-Np hybrid thin films
by Rayna Bryaskova; Daniela Pencheva; Girish M. Kale; Umesh Lad; T. Kantardjiev (pp. 77-85).
TEM of PVA/TEOS/AgNps antibacterial hybrid thin film containing 0.4% AgNO3 heat treated at 100°C for 60 min. showing an average Ag nanoparticles of 6±1.8 nm.Novel hybrid material thin films based on polyvinyl alcohol (PVA)/tetraethyl orthosilicate (TEOS) with embedded silver nanoparticles (AgNps) were synthesized using sol–gel method. Two different strategies for the synthesis of silver nanoparticles in PVA/TEOS matrix were applied based on reduction of the silver ions by thermal annealing of the films or by preliminary preparation of silver nanoparticles using PVA as a reducing agent. The successful incorporation of silver nanoparticles ranging from 5 to 7nm in PVA/TEOS matrix was confirmed by TEM and EDX analysis, UV–Vis spectroscopy and XRD analysis. The antibacterial activity of the synthesized hybrid materials against etalon strains of three different groups of bacteria – Staphylococcus aureus (gram-positive bacteria), Escherichia coli (gram-negative bacteria), Pseudomonas aeruginosa (non-ferment gram-negative bacteria) has been studied as they are commonly found in hospital environment. The hybrid materials showed a strong bactericidal effect against E. coli, S. aureus and P. aeruginosa and therefore have potential applications in biotechnology and biomedical science.
Keywords: Antibacterial; Hybrid films; Nanocomposite; Nanoparticle; Polyvinyl alcohol; Silver; Sol–gel techniques; Silicate
Kaolinite flocculation induced by smectite addition – A transmission X-ray microscopic study
by Marek S. Żbik; Yen-Fang Song; Ray L. Frost (pp. 86-92).
Settling of suspensions containing various addition of smectite normalised to pure kaolinite settling.The influence of smectite addition on kaolinite suspensions in water was investigated by transmission X-ray microscopy (TXM) and Scanning Electron Microscopy (SEM). Sedimentation test screening was also conducted. Micrographs were processed by the STatistic IMage Analysing (STIMAN) program and structural parameters were calculated. From the results of the sedimentation tests important influences of small smectite additions to about 3wt.% on kaolinite suspension flocculation has been found. In order to determine the reason for this smectite impact on kaolinite suspension, macroscopic behaviour micro-structural examination using Transmission X-ray Microscope (TXM) and SEM has been undertaken. TXM & SEM micrographs of freeze-dried kaolinite–smectite suspensions with up to 20% smectite showed a high degree of orientation of the fabric made of highly oriented particles and greatest density when 3wt.% of smectite was added to the 10wt.% dense kaolinite suspension. In contrast, suspensions containing pure kaolinite do not show such platelet mutual orientation but homogenous network of randomly oriented kaolinite platelets. This suggests that in kaolinite–smectite suspensions, smectite forms highly oriented basic framework into which kaolinite platelets may bond in face to face preferential contacts strengthening structure and allowing them to show plastic behaviour which is cause of platelets orientation.
Keywords: Kaolinite flocculation; Smectite gel; Clay micro-structure
Coordination chemistry approach for the end-to-end assembly of gold nanorods
by P.R. Selvakannan; Eddy Dumas; Frédéric Dumur; Christine Péchoux; Patricia Beaunier; Arnaud Etcheberry; Francis Sécheresse; Hynd Remita; Cédric R. Mayer (pp. 93-97).
End-to-end 1D assembly of gold nanorods synthesized by radiolysis has been obtained through selective functionalization and coordination chemistry.Gold nanorods synthesized by radiolysis were selectively end-functionalized by a fully conjugated thiol bearing a pendant terpyridine group; addition of ferrous ions led to the end-to-end 1D self-assembly of the nanorods. Similar results have been obtained when the preformed [(HStpy)Fe(tpySH)]2+ dithiol complex was directly added to the gold nanorods.
Keywords: Gold nanorods; Terpyridine; Coordination complexes; Iron(II) complexes; Radiolysis; 1D assembly
Laccase-modified silica nanoparticles efficiently catalyze the transformation of phenolic compounds
by Patrick Galliker; Gregor Hommes; Dietmar Schlosser; Philippe F.-X. Corvini; Patrick Shahgaldian (pp. 98-105).
Silica nanoparticles have been modified with a laccase and shown to efficiently degrade Bisphenol A in solution.A new system based on laccase-modified silica nanoparticles has been developed and tested for its ability to degrade a major endocrine disrupting chemical, 4,4′-isopropylidenediphenol (bisphenol A). The nanoparticles have been produced using the Stöber method and characterized using scanning electron microscopy, dynamic light scattering and ζ-potential measurements. The introduction of primary amino groups at the surface of these particles has been achieved using an organo-silane (amino-propyl-triethoxy-silane). The use of glutaraldehyde as bi-functional coupling agent allowed the efficient conjugation of a laccase from Coriolopsis polyzona at the surface of the nanoparticles, as monitored by measuring the amount of proteins coupled and the ζ-potential of the produced nanoparticles. The oxidative activity of the so-produced bio-conjugate was tested using radioactive-(14C) labeled bisphenol A. Analytical methods based on high performance liquid chromatography coupled to mass spectrometry and gas chromatography allowing a convenient and reliable study of the enzymatic activity of the produced bio-conjugates have been developed. It is demonstrated that even if a decrease of the specific catalytic activity of the immobilized enzyme is measured, the activity of the bio-conjugate remains compatible with the application of these systems to the transformation of phenolic pollutants. Additionally, the developed analytical methods allowed the identification of the transformation products formed during the enzymatic reaction.
Keywords: Laccase; Silica; Nanoparticle; Bisphenol A; Endocrine disrupting chemical; Radioactivity
Responsive hydrogels with poly( N-isopropylacrylamide- co-acrylic acid) colloidal spheres as building blocks
by Lie-Wen Xia; Xiao-Jie Ju; Jing-Jing Liu; Rui Xie; Liang-Yin Chu (pp. 106-113).
Responsive hydrogels with fast response property are prepared with poly( N-isopropylacrylamide- co-acrylic acid) colloidal spheres as building blocks.Display Omitted► Responsive hydrogels are fabricated with responsive microgels as crosslinkers to crosslink responsive networks. ► Microgel-crosslinked hydrogels exhibit both fast response rate and large volume change ratio to environmental stimuli. ► Response properties of microgel-crosslinked hydrogels are tunable by varying the microgel content.A novel type of microgel-crosslinked hydrogels (MCG), which are constructed with poly( N-isopropylacrylamide- co-acrylic acid) (P(NIPAM- co-AAc)) microgels as building blocks, have been successfully prepared by using functionalized P(NIPAM- co-AAc) microgels as crosslinkers to crosslink the P(NIPAM- co-AAc) networks. The prepared MCG hydrogels are featured with both fast response rate and large volume change ratio to environmental temperature stimuli. The cooperative function of all the fast shrinking of microgels, the fast collapse of the grafted dangling chains on the microgel surfaces and the 3-D interconnected water transportation channels between the microgels and polymeric networks inside the MCG hydrogels make the hydrogels respond fast to the environmental temperature change. The response rate and the volume change ratio of the hydrogel increase with decreasing the functional P(NIPAM- co-AAc) microgel concentration in the hydrogel preparation, which means that the volume-phase transition property of the hydrogel is tunable by simply controlling the microgel content in the hydrogel. The proposed MCG hydrogels with improved thermo-responsive phase transition property are attractive for developing efficient stimuli-responsive smart sensors, actuators, bioseparation absorbants, and so on.
Keywords: Microgels; Colloidal spheres; Hydrogels; Phase transition; Poly(; N; -isopropylacrylamide); Poly(acrylic acid)
Surface-modification-directed controlled adsorption of serum albumin onto magnetite nanocuboids synthesized in a gel-diffusion technique
by Ballav Moni Borah; Bedabrata Saha; Sandeep Kumar Dey; Gopal Das (pp. 114-121).
Adsorption of bovine serum albumin could be controlled by simple hydrophilic and hydrophobic surface modification of magnetite nanocuboids synthesized by a gel-diffusion method.Magnetite nanocuboids have been synthesized via gel-diffusion technique in agarose gel. Here, the agarose gel matrix has been used as an organic template for formation and growth modification of magnetite. Gel mineralization mimics the membrane-based biomineralization, controls the diffusion process and gives the micro/nano environment for the crystal growth. We also attempt to understand the influence of different surface modifications of synthesized magnetite nanocuboids on protein interaction. For this purpose, magnetite particles were coated with trimesic acid (benzene-1,3,5-tricarboxylic acid) and stearic acid, which generates a hydrophilic and a hydrophobic modified surface, respectively. We report controlled adsorption behavior of bovine serum albumin (BSA) by surface modification of magnetite nanocuboids with different functional groups. The adsorption capacity of BSA increases on trimesic acid-coated surfaces compared to bare magnetite surfaces, while it decreases on stearic acid-coated surfaces. In situ fluorescence spectroscopy has been used to analyze the tertiary protein structure in the adsorbed state on these three surfaces. Partial unfolding in the tertiary structure of BSA was observed upon adsorption onto bare magnetite surfaces. On trimesic acid-coated surfaces, tertiary unfolding of BSA was greater than on bare magnetite surfaces, while BSA undergoes minor tertiary structural change on stearic acid-coated surfaces.
Keywords: Magnetite nanoparticle; Gel-diffusion synthesis; Surface modification; Trimesic acid; Stearic acid; BSA adsorption
Influences of MAA on the porous morphology of P(St–MAA) latex particles produced by batch soap-free emulsion polymerization followed by stepwise alkali/acid post-treatment
by Wei Deng; Ronglong Li; Mengjun Zhang; Lixiang Gong; Chengyou Kan (pp. 122-126).
The amount of MAA intensively influenced the morphology of P(St–MAA) latex particles, and the particles showed different morphology after alkali and stepwise alkali/acid post-treatment.Soap-free P(St–MAA) latex particles with variable styrene (St)/methacrylic acid (MAA) ratio were synthesized by batch emulsion copolymerization at 70°C for 7h, and the particles with porous structure were obtained after stepwise alkali/acid post-treatment. The effects of MAA amount on the particle morphologies after the alkali and the stepwise alkali/acid post-treatments were investigated by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Results indicated that the alkali-treated latex particles showed anomalous structure with rough surface, and no hollow was clearly identified inside them. When these alkali-treated particles were further treated with acid solution, the particle surface became much smoother, and porous morphology appeared. It was found that when the MAA amount was less than or equal to 4mol%, no obvious morphological variation was observed; while the latex particles showed clearly porous structure as the MAA amount increased to 6mol%; with the further increase of MAA amount to 8mol%, the pore size decreased distinctly.
Keywords: Soap-free emulsion polymerization; Porous structure; Particle morphology; Stepwise alkali/acid post-treatment; Methacrylic acid
Strong interfacial attrition developed by oleate/layered double hydroxide nanoplatelets dispersed into poly(butylene succinate)
by Qian Zhou; Vincent Verney; Sophie Commereuc; In-Joo Chin; Fabrice Leroux (pp. 127-133).
Poly(butylene succinate) (PBS) nanocomposite structure was studied as a function of the filler percentage loading. The resulting state of dispersion was evaluated by XRD and TEM, and the interfacial attrition between PBS chain and lamellar platelets by the melt rheological properties. Hybrid organic inorganic (O/I) layered double hydroxide (LDH) organo-modified by oleate anions was used as filler. It was found that the confinement supplied by the LDH framework forces the interleaved organic molecule to be more distant from each other than in the case of oleate salt, this having as an effect to decrease strongly the homonuclear intermolecular1H1H dipolar interaction. An additional consequence of this relatively free molecular rotation, affecting the13C CPMAS response as well, is to facilitate the delamination of the 2D-stacked layers during extrusion since an quasi-exfoliated PBS:Mg2Al/oleate structure is observed for filler loading lower than 5% w/w. This is in association to a non-linear viscoelasticity in the low- ω region and the observed shear-thinning tendency compares better than other PBS:silicate nanocomposite derivatives and is here explained by the presence of a percolated LDH nanoparticle network. Indeed the plastic deformation in the low- ω region is found to be restricted by well-dispersed LDH tactoids in association with a rather strong attrition phenomenon between tethered oleate anions and PBS chains.
Keywords: Organic inorganic assembly; Layered double hydroxide; Nanocomposite; Platelets exfoliation; Rheology
Reduced colloidal repulsion imparted by adsorbed polymer of particle dimensions
by Yu Ho Wen; Po-Chang Lin; Chun Yi Lee; Chi Chung Hua; Tai-Chou Lee (pp. 134-141).
The reduced colloidal repulsion in concentrated dispersions is ascribed to polymer bridging and/or a partially screened electrostatic interaction.Display Omitted► Colloidal attractions can be introduced by adsorbed polymer of sizes comparable to particle dimensions. ► The adsorbed polymer results in a reduced surface potential. ► The unsaturated polymer layer is unable to form an effective repulsive shell that is dominant over the electrical double layer.This work investigated the detailed interparticle interactions in a concentrated polymer-coated colloidal system in which the bare colloidal particles and the adsorbed polymers are of comparable size and, hence, the polymer adsorption cannot be foreseen to induce repulsive or attractive interactions. Specifically, poly(ethylene oxide) (PEO) chains (R g∼10nm) adsorbed onto fine silica colloidal particles (SAXS-determined radius ∼7.4nm; width of log-normal size distribution ∼0.28) were considered as a model system, for which the impact of a small amount of polymer adsorption (⩽0.18mg/m2) in controlling the interactions of the PEO-coated silica particles was systematically explored by analyzing the small-angle X-ray scattering (SAXS) data against three interaction potentials—the equivalent hard-sphere (EHS) potential, the Hayter–Penfold–Yukawa (HPY) potential, and the square-well (SW) potential. Moreover, the SAXS analysis was enforced by dynamic light scattering (DLS) for predetermining the adsorption behavior, as well as for evaluating the possibility of polymer bridging. Under a dilute condition, the DLS analysis showed no sign of forming colloidal multiplets. In concentrated dispersions, both the HPY and SW potentials clearly revealed a systematic decrease of colloidal repulsions with increased PEO coverage, ascribed to a partially “screened” electrostatic interaction and/or the formation of PEO-bridged silica doublets. The present findings have interesting implications for controlling the colloidal interactions and microstructures of fine polymer-coated particles in dense or condensed phases.
Keywords: Colloidal interactions; Structure factor; Polymer bridging; Coated colloid; Small-angle X-ray scattering
An unexpected solvent effect on the self-assembly of a 1,7-bis-pyridinoyl perylene diimide amphiphile
by Shuangping Xu; Jin Sun; Damei Ke; Guojun Song; Wei Zhang; Chuanlang Zhan (pp. 142-147).
In this paper, we present an unexpected solvent effect between methanol and ethanol on the self-assembly of a 1,7-bis-pyridinoyl perylene diimide amphiphile.In this paper, we report that a 1,7-bis-pyridinoyl perylene diimide amphiphile undergoes distinctly different self-assembly in methanol compared to ethanol. This amphiphile forms hollow nanospheres in methanol, whereas in ethanol, it self-assembles into microrose flowers which consist of several soft nanoplates packing like rose petals. Studies of the concentration-dependent absorption spectra confirmed this solvent effect. The most distinct spectral features were the A0–0/ A0–1 and A0–0/A S0– S2 values. These spectral changes were explained in terms of the Franck–Condon factors.
Keywords: Perylene diimide; Self-assembly; Solvent effect; π; –; π; Stacking interaction; Amphiphile
Competing effects of silanol surface concentration and solvent dielectric constant on electrostatic layer-by-layer assembly of silica nanoparticles on gold
by Ruidong Yang; Feng Wang; Richard H. Blunk; Anastasios P. Angelopoulos (pp. 148-152).
AFM image (10μm×10μm) of six layers of silica nanoparticles (65nm diameter) electrostatically assembled with cationic polyacrylamide on gold.Two types of silica nanoparticles having differing concentrations of ionizable surface groups are used to investigate the interplay between nanoparticle surface charge and solvent dielectric constant in nanostructure development during layer-by-layer assembly with a cationic polyacrylamide. Zeta ( ζ) potential measurements are used to determine the extent of silanol dissociation with pH. For 19-nm-diameter X-Tec 3408 silica nanoparticles from Nano-X GmbH (NanoX), complete dissociation yields a ζ-potential value of about −44mV and occurs between pH 5 and 6 in 50% ethanol-in-water mixture by volume. By contrast, 65-nm-diameter polishing silica from Electron Microscopy Supply (EMS) has a ζ potential that does not equilibrate even up to pH 7 with a value of −59mV under otherwise similar solution conditions. The more negative zeta potential at a given pH is found to substantially reduce nanoparticle adsorption. This behavior is opposite that observed when the dielectric constant of the suspension is decreased, independent of particle size. Nanoparticle surface chemical heterogeneity is discussed as a plausible explanation for such seriously discrepant behavior and the effects on multilayer electrical contact resistance for proton-exchange membrane (PEM) fuel-cell coating applications are presented.
Keywords: Layer-by-layer assembly; Adsorption; Silica; Nanoparticles; Gouy–Chapman theory; Zeta potential
Multidrug nanoparticles based on novel random copolymer containing cytarabine and fluorodeoxyuridine
by Cui Yin; Xia Li; Qi Wu; Jun-Liang Wang; Xian-Fu Lin (pp. 153-158).
The self-assembly of novel multidrug random copolymer containing cytarabine and fluorodeoxyuridine.Novel multidrug nanoparticles were self-assembled from the random copolymer containing cytarabine and fluorodeoxyuridine. The multidrug copolymer carrying 28.7wt.% of cytarabine and 29.1wt.% of fluorodeoxyuridine was prepared by radical polymerization combined with enzymatic selective transesterification. Homopolymers of the two drugs were also synthesized by the same method. And the polymers were characterized by FTIR,1H NMR, and gel permeation chromatography (GPC). Self-assembly of the multidrug copolymer was verified by UV–vis and fluorescence spectroscopy. The morphology of nanoparticles formed from the copolymer was investigated by transmission electron microscopy (TEM) and dynamic light scattering (DLS), which indicated that the nanoparticles were regular spheres with a diameter of 133±28nm. In vitro drug release studies illustrated that the two synergistic anticancer agents could be simultaneously released from the multidrug nanoparticles.
Keywords: Multidrug nanoparticles; Combination therapy; Drug delivery systems; Cytarabine; Fluorodeoxyuridine
One solvent, one pot and free capping ligands: Synthesis of alloyed multipod-branched Cd xZn1− xS nanocrystals
by Xiaobo He; Lian Gao (pp. 159-165).
The alloyed multipod-branched Cd xZn1− xS (0< x<1) NCs have been prepared through a simple solvothermal approach using one solvent ethanolamine without any capping ligands.The solvent ethanolamine with the assistance of cationic doping has been applied to synthesize alloyed multipod-branched Cd xZn1− xS (0< x<1) nanocrystals through a simple solvothermal route. During the growth of the alloyed multipod-branched nanocrystals, for one thing, the cationic doping enlarges the energy difference between wurtzite and zinc-blende phases; for another thing, the –OH groups of ethanolamine favor the thorough alloying effects and the formation of the zinc-blende-structured seeds, while the –NH2 groups facilitate the subsequent preferential growth of the wurtzite-phased arms. The composition x of the alloyed multipod-branched Cd xZn1− xS nanocrystals can be facilely tuned by Cd/Zn initial molar ratios. Furthermore, the absorption edges (corresponding to optical band gapsE g) and the near-band-edge emission peaks are varied with the doping Cd2+ content x. It is reasonable for us to believe that ethanolamine can also be employed to fabricate other alloyed multipod-branched nanocrystals such as CdS xSe1− x, CdSe xTe1− x and CdS xTe1− x.
Keywords: Alloys; Ethanolamine; Functional groups; Multipod-branched nanocrystals
Preparation and luminescence properties of Lu2O3:Eu3+ nanofibers by sol–gel/electrospinning process
by Xue Li; Min Yu; Zhiyao Hou; Wenxin Wang; Guogang Li; Ziyong Cheng; Ruitao Chai; Jun Lin (pp. 166-172).
One-dimensional Lu2O3:Eu3+ nanofibers have been prepared by a combination method of sol–gel process and electrospinning. The as-formed precursor samples present uniform fiberlike morphology. After annealing the precursors at 900°C, the Lu2O3:Eu3+ nanofibers are uniform with diameters ranging from 90 to 180nm. Under ultraviolet excitation and the low-voltage electron beam excitation, Lu2O3:Eu3+ nanofibers all exhibit typical red (612nm) emission corresponding to5D0–7F2 transition of Eu3+.One-dimensional Lu2O3:Eu3+ nanofibers have been prepared by a combination method of sol–gel process and electrospinning technology. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric and differential thermal analysis (TG–DTA), scanning electron microscopy (SEM), energy-dispersive X-ray spectrum (EDS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL), and cathodoluminescence (CL) spectra were used to characterize the samples. The XRD, FT-IR and TG–DTA results show that Lu2O3:Eu3+ samples crystallize at 900°C. SEM images indicate that as prepared precursor samples and those annealed at 900°C present uniform fiberlike morphology. After being heated at 900°C, the diameters of fibers decrease greatly, ranging from 90 to 180nm. TEM image further manifests that the as-formed Lu2O3:Eu3+ nanofibers consist of nanoparticles (the crystallite size is about 16.5nm). Under the short wavelength ultraviolet irradiation and the low-voltage electron beam excitation, Lu2O3:Eu3+ nanofibers all exhibit typical red (5D0–7FJ) emission. The optimum doping concentration of Eu3+ in the Lu2O3 nanofibers also has been investigated.
Keywords: Electrospinning; Lu; 2; O; 3; Europium; Luminescence; Nanofibers
Synthesis of colloidal silica nanoparticles of a tunable mesopore size and their application to the adsorption of biomolecules
by Antonio B. Fuertes; Patricia Valle-Vigón; Marta Sevilla (pp. 173-180).
The colloidal mesoporous silica nanoparticles exhibit a high affinity for the adsorption of bulky biomolecules (i.e. hemoglobin or lysozyme) being most of these molecules adsorbed outside of the nanoparticles.A synthetic method for the fabrication of colloidal mesoporous silica nanoparticles of a tunable mesopore size is presented. These nanoparticles form stable colloidal suspensions, have narrow particle size distributions in the 50–300nm range and exhibit a framework-confined porosity made up of large mesopores with a diameter of up to 9nm. The size of the mesopores was enlarged by means of two different swelling agents (SA), i.e. 1,3,5-trimethylbenzene (TMB) and N, N-dimethylhexadecylamine (DMHA). Colloidal mesoporous silica nanoparticles exhibit a strong affinity for the adsorption of hemoglobin (Hb) and the immobilization of lysozyme (Lz). These nanoparticles can adsorb up to 2080mgHbg−1 support and 690mgLzg−1 support. Moreover, the adsorption of these biomolecules on silica nanoparticles occurs very quickly and most of what is adsorbed is accommodated on the external surface area of the silica nanoparticles.
Keywords: Mesoporous materials; Silica; Colloidal nanoparticles; Adsorption of biomolecules; Hemoglobin; Lysozyme
Interface-hydrothermal synthesis and electrochemical properties of CoS x nanodots/poly(sodium-4-styrene sulfonate) functionalized multi-walled carbon nanotubes nanocomposite
by Changzhou Yuan; Laifa Shen; Fang Zhang; Xiangjun Lu; Diankai Li; Xiaogang Zhang (pp. 181-185).
Amorphous CoS x nanodots highly dispersed onto the poly(sodium-4-styrene sulfonate) functionalized multi-walled carbon nanotubes were synthesized by unique interface-hydrothermal method and delivered good electrochemical capacitance at high rates.In the work, amorphous CoS x nanodots were highly dispersed onto poly(sodium-4-styrene sulfonate) (PSS) functionalized multi-walled carbon nanotubes (FMWCNTs) by a interface-hydrothermal method. Electrochemical data demonstrated a specific capacitance (SC) of 300Fg−1 was delivered at 3Ag−1 by the nanocomposite, which was 90% of that at 0.4Ag−1, indicating its good rate response. The good dispersion of the electroactive CoS x nanodots onto the FMWCNTs should be responsible for its better supercapacitive performance. Such unique structure made the abundant electroactive surface atoms of the CoS x phase contacted by OH− ions and electrons easily through the three-dimensional mesoporous conducting matrix of FMWCNTs for fast energy storage. Furthermore, the SC retention of ca. 95% reveals a good electrochemical stability of the nanocomposite.
Keywords: Cobalt sulfide nanodots; Poly(sodium-4-styrene sulfonate) functionalized multi-walled carbon nanotubes; Nanocomposite; Electrochemical capacitors
Agglomeration and filtration of colloidal suspensions with DVLO interactions in simulation and experiment
by Bastian Schäfer; Martin Hecht; Jens Harting; Hermann Nirschl (pp. 186-195).
The combination of molecular dynamics (MD), stochastic rotation dynamics (SRD) and lattice Boltzmann (LB) simulations permits to study the agglomeration of colloidal particles (left), the filtration (right) and the permeation of the compressed filter cakes (right).Cake filtration is a widely used solid–liquid separation process. However, the high flow resistance of the nanoporous filter cake lowers the efficiency of the process significantly. The structure and thus the permeability of the filter cakes depend on the compressive load acting on the particles, the particles size, and the agglomeration of the particles. The latter is determined by the particle charge and the ionic strength of the suspension, as described by the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. In this paper, we propose a combined stochastic rotation dynamics (SRD) and molecular dynamics (MD) methodology to simulate the cake formation. The simulations give further insight into the dependency of the filter cakes’ structure on the agglomeration of the particles, which cannot be accessed experimentally. The permeability, as investigated with lattice Boltzmann (LB) simulations of flow through the discretized cake, depends on the particle size and porosity, and thus on the agglomeration of the particles. Our results agree qualitatively with experimental data obtained from colloidal boehmite suspensions.
Keywords: Colloids; Agglomeration; Filtration; Molecular dynamics; Stochastic rotation dynamics; Lattice Boltzmann
Nanoindentation of surfactant aggregates
by Patrick Y. Chiu; Kunal Shah; Susan B. Sinnott (pp. 196-204).
Surfactant-covered carbon nanotube indenting adsorbed CTAB micelle on silica by molecular dynamics simulation.Display Omitted►Classical molecular dynamics simulations provide predictions about the morphology of surfactant aggregates at hydrophobic and hydrophilic solid–liquid interfaces of varying curvature. ►Adsorbed surfactants on carbon nanotubes create steric repulsion between the nanotubes that exceed the van der Waals forces of attraction. ►Nanoindentation of a micelle with a tip of sharp curvature shows a steady rise in force as the escaped surfactant monomers climbed up the indenter. ►Nanoindentation with a surfactant-covered tip of the same sharp curvature is predicted to have the same separation distance to break the micelle and comparable mechanical breakdown mechanisms as a tip that is not surfactant-covered.Surfactants are important for a wide range of applications dealing with one-dimensional nanoscale materials, including dispersion of carbon nanotubes, as organic templates in mesoporous silica thin films, and for the fabrication of silica nanowires. There is therefore great interest in better understanding the structure and properties of surfactant aggregates at the solid–liquid interface. Here, classical molecular dynamics simulations with empirical potentials are used to compare the structures and mechanical properties of cationic surfactant micelles that are being indented with carbon nanotubes and silica nanowires at the silica–water interface. The findings are compared to the results of bulk indentation with graphite and silica surfaces, and the influence of nanometer-scale curvature on the results is described.
Keywords: Molecular dynamics; Micelles; Nanotubes; Nanowires; Indentation
Surface segregation of fluorinated moieties on poly(methyl methacrylate- ran-2-perfluorooctylethyl methacrylate) films during film formation: Entropic or enthalpic influences
by XiuYun Ye; Biao Zuo; Mao Deng; Yanlin Hei; Huagang Ni; Xiaolin Lu; Xinping Wang (pp. 205-214).
Entropic or enthalpic forces dominated segregation of fluorinated moieties on the film surface was related to the content of FMA in poly(MMA- ran-FMA) copolymers.The effects of solvents, fluorinated monomer content and film-formation methods on the surface structures of random copolymers composed of methyl methacrylate (MMA) and 2-perfluorooctylethyl methacrylate (FMA) were investigated by contact angle goniometry, X-ray photoelectron spectroscopy, sum frequency generation (SFG) vibrational spectroscopy and surface tension measurement. It is found that, with cyclohexanone as the solvent, there is a critical FMA content of 9mol%, below which the copolymer films by spin coating have a more surface segregation extent of fluorinated moieties than those by solution casting; above which the copolymer films by solution casting have a more surface segregation extent of fluorinated moieties than those by spin coating. However, with toluene as solvent, the critical FMA content lowers down to 3mol%. We believe that the solvent nature and the content of fluorinated moieties in the random copolymer have the great effect because the combined effect of these two factors can determine the random copolymer chain conformations and their thermodynamic dominating factors in the solution and at the solution–air interface. A thermodynamic analysis combining the entropic and enthalpic effects is suggested to explain the observed phenomenon. This research is believed to obtain an enhanced understanding of the surface formation mechanism of the polymer films and thus demonstrate how to promote the segregation of fluorinated moieties at the polymer film surfaces.
Keywords: Surface segregation; Random copolymer; Film-formation method; Thermodynamic effect; Solvent effect
Monolayers of mixture of alkylaminomethyl rutin and lecithin at the air/water interface
by Fang He; Rui-xia Li; Da-cheng Wu (pp. 215-223).
The subphase pH dependence of surface behavior of the pseudo-amphoteric alkylaminomethyl rutin at the air/water interface.A compound of flavonol-based biosurfactant, as C8-substituted alkylaminomethyl rutin (DAMR) for a potential pharmaceutical or agrochemical use, was prepared experimentally. The surface behavior of DAMR and its mixture with lecithin from soybean (SL) had been studied. DAMR, regarded as a pseudo-amphoteric character, exhibits both liquid-condensed (LC) and liquid-expanded (LE) phases while SL is in the form of the LE phase only. The phase parameters of DAMR (including Alimt, πcoll) are observed to strongly depend on both the subphase temperature and the pH, which regulate the degree of ionization. In addition, the observed positive deviation calculated from excess Gibbs free energies of the DAMR–SL system suggests a repulsive interaction between DAMR and SL at all XDAMR values. Also the interaction parameter is found to increase linearly with surface pressure, regardless of composition. Notably, the relationship of logarithmic activity coefficient vs.XDAMR2 reveals that the molecular interaction of DAMR–SL can be adequately simulated using a simple regular mixture model. Importantly, lowerCS-1 values of this mixture than those with pure DAMR and SL denote weak elasticity of mixed monolayers with values of XDAMR of 0.2–0.8, indicating that the direct addition of DAMR may exert a somewhat adverse influence on SL membranes.
Keywords: Rutin; Lecithin; Alkylaminomethyl rutin; Mixed Langmuir monolayers; Air/water interface
Liquid crystalline phases of 1,2-dimethyl-3-hexadecylimidazolium bromide and binary mixtures with water
by Cuihua Li; Jinhua He; Jianhong Liu; Lian-an Qian; Zhenqiang Yu; Qianling Zhang; Chuanxin He (pp. 224-229).
1,2-Dimethyl-3-hexadecylimidazolium bromide exhibits a thermotropic SmA2 phase from 90.3 to 232.1°C and a lyotropic crystalline phase between 0.5 and 25°C in binary mixtures with water.Display Omitted► 1,2-dimethyl-3-hexadecylimidazolium bromide exhibits thermotropic SmA2 phase behavior. ► The layer spacing in SmA2 phase displays linear temperature dependence. ► H1 phase forms in the mixtures of 1,2-dimethyl-3-hexadecylimidazolium bromide and water. ► In the H1 phase, the cylinder units with D about 4.97±0.04 nm nearly reach the most dense and highest-ordered columnar structure.1,2-Dimethyl-3-hexadecylimidazolium bromide, which lacks an acidic proton at the C-2 imidazolium ring position, exhibits thermotropic SmA2 phase behavior above its melting point of 90.3°C and up to 232.1°C. The corresponding layer spacing and the full width at half maximum from XRD patterns display a temperature dependence. In binary mixtures with water, over a concentration range of 40–75%, lyotropic liquid crystalline phases form between 0.5 and 25°C. The molecules of the new ionic liquid (IL) in the binary mixtures show three different self-assembly processes, namely, formation of rod micelles, coexistence of rod micelles and a hexagonal phase, and a pure hexagonal phase. The distance between the two centers of adjacent columns of cylinder units remains nearly constant at 4.97±0.04nm when the IL content exceeds 70%, indicating that the cylinder units attain a dense and highly ordered packing.
Keywords: 1,2-Dimethyl-3-hexadecylimidazolium bromide; Thermotropic liquid crystalline; Lyotropic liquid crystalline; SAXS
Evaluation of alkyl sulfate and sulfonate micellar structure at the water–surfactant interphase with simple geometrical calculations
by Giuseppe Del Re; G. D’Errico; O. Ortona; V. Vitagliano (pp. 230-235).
The different exposure of the surfactant’ headgroups on the micellar surface could be the origin of the tendency of sodium decylsulfate to form ellipsoidal aggregates, whereas for sodium decylsulfonate nearly spherical micelles are preferentially.Display Omitted► Simple geometrical consideration allows analysis of micellar microstructure. ► The orientation of sulfate and sulfonate head groups on the micelle surface is different. ► The shape of alkyl sulfate and sulfonate micelles is different.The present work deals with an interpretation of the differences in micellar structure of two surfactants, sodium decyl sulfonate and sodium decyl sulfate, whose only difference in molecular structure is the presence, for sulfate, of an oxygen atom bridging alkyl chains from a commonSO3- charged head group. Using a simple geometrical approach, a different exposure of the surfactant head groups on the micellar surface is proposed. It is also shown that the different interphase microstructure could be the reason that decyl sulfate forms ellipsoidal aggregates, in contrast to decyl sulfonate, which forms nearly spherical micelles.
Keywords: Surfactant; Micelle; Molecular geometry; Head group
Rheological study of hydrophobically modified hydroxyethyl cellulose and phospholipid vesicles
by Yu Yuan Chieng; Shing Bor Chen (pp. 236-245).
Interaction between HMHEC and phospholipid vesicles.The rheological behavior of hydrophobically modified hydroxyehtyl cellulose (HMHEC) was studied in the presence of phospholipid vesicles. The effects of sonication, lipid species and concentration on the rheology were investigated at two HMHEC concentrations: 0.3wt.% and 0.7wt.%. It is found that compared to a pure HMHEC solution, the mixture viscosity could be enhanced by more than one order of magnitude for sonicated samples at certain lipid concentrations. The viscosity, which depends on the vesicle size and concentration, first increases with the lipid concentration and then decreases. Besides, the lipid addition increases the plateau modulus. These observed rheological behaviors can be explained by two types of association; some of the hydrophobes aggregate to form micelles, while others are embedded in the vesicle bilayers. By this means, the vesicles can be interconnected, contributing to the viscosity enhancement.
Keywords: Associative polymer; Phospholipid; Vesicles; Concentration; Viscosity; Modulus
Effect of MnO x modification on the activity and adsorption of CuO/Ce0.67Zr0.33O2 catalyst for NO reduction
by Lianjun Liu; Qiang Yu; Jie Zhu; Haiqin Wan; Keqin Sun; Bin Liu; Haiyang Zhu; Fei Gao; Lin Dong; Yi Chen (pp. 246-255).
The introduction of MnO x onto CuO/Ce0.67Zr0.33O2 assists in a rapid change of the copper valence, and activates the adsorbed NO species, thus promoting the activity for NO reduction.The present work explored the effect of MnO x modification on the activity and adsorption of CuO/Ce0.67Zr0.33O2 catalyst for NO reduction by CO. XRD, Raman, UV, XPS, H2-TPR, and in situ FT-IR were used to characterize these catalysts. Results suggested that the incorporation of copper and manganese species resulted in the lattice expansion and the decease of microstrain of ceria–zirconia, thus inducing the formation of oxygen vacancies. There was a strong interaction between surface copper, manganese, and the support via charge transfer. The addition of manganese species could promote the reduction of the resultant catalysts and assist copper oxide in changing the valence and the support in supplying oxygen. These reduction behaviors were dependent on the loading amounts of MnO x and the impregnation procedure. In addition, the introduction of MnO x cannot change the adsorption type of NO, but readily helped to activate the adsorbed NO species. As a result, these factors were responsible for the enhancement of activity and selectivity through MnO x modification.
Keywords: Interaction; Manganese modification; In situ FT-IR; CO adsorption; Nitrates
Equilibrium and kinetic adsorption study of the adsorptive removal of Cr(VI) using modified wheat residue
by Suhong Chen; Qinyan Yue; Baoyu Gao; Xing Xu (pp. 256-264).
The functional groups introduced into wheat residue and modified wheat straw were determined by infrared spectra analysis.A new adsorbent modified from wheat residue was synthesized after reaction with epichlorohydrin and triethylamine by using the modifying agents of diethylenetriamine in the presence of organic medium of N,N-dimethylformamide. The performance of the modified wheat straw (MWS) was characterized by Fourier transform infrared spectroscopy and point of zero charge analysis. The adsorption was investigated in a batch adsorption system, including both equilibrium adsorption isotherms and kinetics. Results showed that MWR had great anion-adsorbing capacity, due to the existence of a large number of introduced amino groups, and the value of pHPZC was around 5.0. Equilibrium data were analyzed using the Langmuir, Freundlich, and Temkin isotherm models and were found to be best represented by the Freundlich isotherm model. Evaluation of the adsorption process identified its endothermic nature. The maximum adsorption capacity of MWS for the removal of Cr(VI) was 322.58mg/g at 328K, indicating that MWS has high chromium removal efficiency, compared to other adsorbents reported. The kinetics of adsorption followed the pseudo-second-order kinetic equation. The mechanism of adsorption was investigated using the intraparticle diffusion model. Thermodynamic parameters (free energy change, enthalpy change, and entropy change) revealed that the adsorption of Cr(VI) onto MWS was endothermic and spontaneous; additionally, the adsorption can be characterized as an ion-exchange process. The results suggest that MWS is an inexpensive and efficient adsorbent for removing Cr(VI) ions from aqueous solution.
Keywords: Modified wheat straw; Cr(VI); Adsorption; Equilibrium isotherms; Kinetics
Protein interactions with bottle-brush polymer layers: Effect of side chain and charge density ratio probed by QCM-D and AFM
by Geoffrey Olanya; Esben Thormann; Imre Varga; Ricardas Makuška; Per M. Claesson (pp. 265-274).
The interaction of proteins with silica surfaces coated with a bottle-brush polymer with high PEO grafting density.Silica surfaces were coated with a range of cationic bottle-brush polymers with 45 units long poly(ethylene oxide) side chains, and their efficiency in reducing protein adsorption was probed by QCM-D, reflectometry and AFM. Preadsorbed layers formed by bottle-brush polymers with different side chain to charge ratio was exposed to two proteins with different net charge, lysozyme and BSA. The reduction in protein adsorption was found to depend on both the type of protein and on the nature of the polyelectrolyte layer. The most pronounced reduction in protein adsorption was achieved when the fraction of charged backbone segments was in the range 0.25–0.5 equivalent to a fraction of poly(ethylene oxide) side chains of 0.75–0.5. It was concluded that these polymers have enough electrostatic attachment points to ensure a strong binding to the surface, and at the same time a sufficient amount of poly(ethylene oxide) side chains to counteract protein adsorption. In contrast, a layer formed by a highly charged polyelectrolyte without side chains was unable to resists protein adsorption. On such a layer the adsorption of negatively charged BSA was strongly enhanced, and positively charged lysozyme adsorbed to a similar extent as to bare silica. AFM colloidal probe force measurement between silica surfaces with preadsorbed layers of bottle-brush polymers were conducted before and after exposure to BSA and lysozyme to gain insight into how proteins were incorporated in the bottle-brush polymer layers.
Keywords: Protein repellency; Protein adsorption; Surface forces; AFM; QCM-D; Reflectometry; BSA; Lysozyme; Bottle-brush polymer
N2-BET specific surface area of bentonites
by S. Kaufhold; R. Dohrmann; M. Klinkenberg; S. Siegesmund; K. Ufer (pp. 275-282).
The SSAN2BET of bentonites was proven to depend on accessible regions of the interlayer (EIA) and hence depends both on the layer charge density and on the valence of the counterion.The specific surface areas (SSAN2BET) of 36 different bentonites had larger values for Ca2+/Mg2+ bentonites than for Na+ bentonites. This trend could not be explained by the different d(001) values nor by the different microstructures. The investigation of Cu-triene-exchanged smectites, which on drying at 105°C still had a d(001) value accounting for approximately 13Å, proved that the SSAN2BET of low-charged smectites increased more than that of high-charged smectites. This could be explained by: (i) more space between the permanent charge sites in the case of low-charged smectites and (ii) the fact that the layers of Cu-triene smectites do not collapse at 105°C. In contrast the SSAN2BET of Ca2+-exchanged bentonites could not be related to the layer charge density (LCD) as in the case of the Cu-triene-exchanged bentonites which is probably due to the varying number of collapsed layers. In conclusion, the SSAN2BET of bentonites which is known to be largely variable is probably determined by microporosity resulting from the quasi-crystalline overlap region and accessible areas of the interlayer. The number of layers per stack and the microstructure are supposed to play a subordinate role. The larger SSAN2BET of Ca/Mg bentonites compared to Na bentonites probably can be explained by the larger space between the charges in the case of the presence of divalent cations.
Keywords: Bentonite; Specific surface area; Smectites
Adsorption and corrosion-inhibiting effect of Dacryodis edulis extract on low-carbon-steel corrosion in acidic media
by E.E. Oguzie; C.K. Enenebeaku; C.O. Akalezi; S.C. Okoro; A.A. Ayuk; E.N. Ejike (pp. 283-292).
Dacryodis edulis extract was studied as a corrosion inhibitor for mild steel in acidic media. The electronic structures of the extract components (A) ascorbic acid, (B) β-caryophyllene and (C) an alkaloid (HBMB) show that the molecules could be adsorbed on the corroding metal surface, and thus retard the corrosion reaction.Display Omitted► The absorbed organic constituents inhibit corrosion. ► Inhibiting effects of the different extract constituents vary randomly. ► Their individual effects depend on envirionmental conditions.The inhibition of low-carbon-steel corrosion in 1M HCl and 0.5M H2SO4 by extracts of Dacryodis edulis (DE) was investigated using gravimetric and electrochemical techniques. DE extract was found to inhibit the uniform and localized corrosion of carbon steel in the acidic media, affecting both the cathodic and anodic partial reactions. The corrosion process was inhibited by adsorption of the extracted organic matter onto the steel surface in a concentration-dependent manner and involved both protonated and molecular species. Molecular dynamics simulations were performed to illustrate the process of adsorption of some specific components of the extract.
Keywords: Steel; Acid corrosion; Plant extracts; Molecular modeling; Adsorption
Amino-functionalized Fe3O4@SiO2 core–shell magnetic nanomaterial as a novel adsorbent for aqueous heavy metals removal
by Jiahong Wang; Shourong Zheng; Yun Shao; Jingliang Liu; Zhaoyi Xu; Dongqiang Zhu (pp. 293-299).
High adsorption capacity, sufficient stability, easy separation, and regeneration properties make amino-functionalized Fe3O4@SiO2 magnetic nanoparticles superior adsorbents for removal of heavy metal ions.A novel amino-functionalized Fe3O4@SiO2 magnetic nanomaterial with a core–shell structure was developed, aiming to remove heavy metal ions from aqueous media. The structural, surface, and magnetic characteristics of the nanosized adsorbent were investigated by elemental analysis, FTIR, N2 adsorption–desorption, transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, vibrating sample magnetometry, thermogravimetric analysis, and zeta-potential measurement. The amino-functionalized Fe3O4@SiO2 nanoadsorbent exhibited high adsorption affinity for aqueous Cu(II), Pb(II), and Cd(II) ions, resulting from complexation of the metal ions by surface amino groups. Moreover, the adsorption affinity for heavy metal ions was not much impacted by the presence of a cosolute of humic acid (10.6mg/L) or alkali/earth metal ions (Na+, K+, Mg2+) (0.025–0.30mmol/L). The metal-loaded Fe3O4@SiO2–NH2 nanoparticles could be recovered readily from aqueous solution by magnetic separation and regenerated easily by acid treatment. Findings of the present work highlight the potential for using amino-functionalized Fe3O4@SiO2 magnetic nanoparticles as an effective and recyclable adsorbent for the removal of heavy metal ions in water and wastewater treatment.
Keywords: Fe; 3; O; 4; @SiO; 2; magnetic nanomaterial; Amino-functionalized; Adsorption; Heavy metal removal
Microemulsion phase as a medium for electrodeposition of nickel and electron-transfer study of ferrocyanide–ferricyanide redox system
by V. Ganesh; V. Lakshminarayanan (pp. 300-306).
The dual role of the W/O microemulsion phase as a template for the electrodeposition of nickel and as an electrolytic medium to study the electron-transfer process of a redox probe is reported.We report our electrochemical studies in a W/O microemulsion phase consisting of a ternary mixture of water, Triton X-100, and toluene. The microemulsion phase plays the dual role of a template in the electrodeposition of nickel and as an electrolytic medium in the study of electron-transfer kinetics. The nickel electrodeposits obtained using this microemulsion phase as a template were characterized by surface analysis techniques such as scanning electron microscopy (SEM) and X-ray diffraction (XRD) studies while cyclic voltammetry (CV) was used to determine the electro-active true surface area of the template-deposited nickel. For electron-transfer studies, CV and electrochemical impedance spectroscopy were employed using potassium ferro/ferricyanide as a redox probe. In contrast to the diffusion-controlled process of the redox probe in aqueous medium, a charge-transfer control was observed in the W/O microemulsion phase. We found that the rate constant value for this particular redox reaction in the microemulsion phase is decreased by about four orders of magnitude when compared to the corresponding value in aqueous medium. The observed phenomenon has been correlated to the structure of the W/O microemulsion phase at the interface, exhibiting a microelectrode array behavior.
Keywords: Electrodeposition; Electron-transfer kinetics; Microemulsion; Microelectrode array
Adsorption equilibrium and kinetics of fluoride on sol–gel-derived activated alumina adsorbents
by Lucy M. Camacho; Arely Torres; Dipendu Saha; Shuguang Deng (pp. 307-313).
Comparison of kinetic model predcitions with experimental data of fluoride removal from a Mexican groundwater using CaO-AA and MnO2-AA.Adsorption equilibrium and kinetics of fluoride on a sol–gel-derived activated alumina and its modifications with calcium oxide or manganese oxide were studied to explore the feasibility of applying these adsorbents for fluoride removal from drinking water. The activated alumina adsorbents were characterized with SEM/EDS and N2-adsorption for their chemical and pore textural properties. The adsorption isotherms were correlated with the Langmuir and Freundlich adsorption equations. The fluoride adsorption isotherms on the sol–gel-derived activated alumina followed the Freundlich model while the fluoride adsorption isotherms on the calcium oxide- or manganese oxide-modified activated alumina adsorbents followed the Langmuir model. The calcium oxide-modified alumina adsorbent showed the highest fluoride adsorption capacities of 0.99 and 96.23mg/g at fluoride concentrations of 0.99 and 432mg/L, respectively. A pseudo-second-order model and an intraparticle kinetic model fitted well the adsorption kinetic data. It was found that both external and intraparticle diffusions contribute to the rate of removal of fluoride from the activated alumina-based adsorbents produced in our laboratory. The adsorption kinetic models evaluated in this work fitted well the adsorption uptake of fluoride from a Mexican groundwater on both calcium oxide- and manganese oxide-modified alumina adsorbents.
Keywords: Fluoride; Adsorption; Equilibrium; Kinetics; Activated alumina; Calcium oxide; Manganese oxide
Uptake properties of phosphate on a novel Zr–modified MgFe–LDH(CO3)
by Ramesh Chitrakar; Satoko Tezuka; Junji Hosokawa; Yoji Makita; Akinari Sonoda; Kenta Ooi; Takahiro Hirotsu (pp. 314-320).
Zr–modified MgFe–layered double hydroxide is a composite of MgFe–LDH(CO3)/Zr hydroxide. The presence of Zr hydroxide particles on the surface of LDH sheets exhibits high selectivity for phosphate in seawater.We prepared a novel Zr–modified MgFe–LDH(CO3) composite by adding a mixed solution of MgCl2, FeCl3, and ZrOCl2 and another mixed solution of 1mol/dm3 NaOH and 1mol/dm3 Na2CO3 to distilled water at a constant pH of 10. The composite exhibited only a poorly crystalline structure, resembling that of layered double hydroxides (LDH) from X-ray diffraction. The phosphate uptake is dependent on pH, decreasing with an increase in pH. This composite shows a much greater uptake of phosphate ions in P-enriched seawater (0.33mg-P/dm3) than amorphous zirconium oxide and MgFe–LDH(CO3). The uptake isotherm was fitted with a Freundlich relation. These phosphate-uptake behaviors closely resemble those of the relevant Zr–MgAl–LDH, which is estimated to be a composite of MgAl–LDH with amorphous zirconium hydroxide on the surface from X-ray absorption spectroscopy. Therefore, a similar structure of Zr–modified MgFe–LDH(CO3) composite probably causes the marked increase in phosphate uptake from P-enriched seawater.
Keywords: Layered double hydroxides; Composite; Selectivity; Phosphate; Seawater
The system of carbon tetrachloride and closed carbon nanotubes analyzed by a combination of molecular simulations, analytical modeling, and adsorption calorimetry
by Sylwester Furmaniak; Artur P. Terzyk; Gerhard Rychlicki; Marek Wiśniewski; Piotr A. Gauden; Piotr Kowalczyk; Karolina M. Werengowska; Katarzyna Dulska (pp. 321-330).
The results of simultaneous fitting of experimental adsorption and enthalpy data using the proposed model. The applicability of the model was tested based on GCMC simulation results.Using the combined techniques of molecular simulation, simple analytical modeling, and adsorption calorimetry, we propose new models describing adsorption onto closed carbon nanotubes. The models are capable of describing the adsorption isotherms and calorimetric enthalpy of carbon tetrachloride adsorption measured on three different closed carbon nanotubes. It is shown that the assumption of the presence of two types of surface centers (high- and low-energy centers) on external tube surfaces is sufficient to describe experimental adsorption and calorimetric enthalpy data.
Keywords: Adsorption; Calorimetry; Carbon nanotubes; GCMC; Modeling; Molecular simulation
Bénard instabilities in a binary-liquid layer evaporating into an inert gas
by H. Machrafi; A. Rednikov; P. Colinet; PC. Dauby (pp. 331-353).
The solutal Marangoni mechanism tends to be by far predominant in what the instability threshold is concerned, the latter being well captured within a Pearson-like model.A linear stability analysis is performed for a horizontal layer of a binary liquid of which solely the solute evaporates into an inert gas, the latter being assumed to be insoluble in the liquid. In particular, a water-ethanol system in contact with air is considered, with the evaporation of water being neglected (which can be justified for a certain humidity of the air). External constraints on the system are introduced by imposing fixed “ambient” mass fraction and temperature values at a certain effective distance above the free liquid–gas interface. The temperature is the same as at the bottom of the liquid layer, where, besides, a fixed mass fraction of the solute is presumed to be maintained. Proceeding from a (quasi-)stationary reference solution, neutral (monotonic) stability curves are calculated in terms of solutal/thermal Marangoni/Rayleigh numbers as functions of the wavenumber for different values of the ratio of the gas and liquid layer thicknesses. The results are also presented in terms of the critical values of the liquid layer thickness as a function of the thickness of the gas layer. The solutal and thermal Rayleigh and Marangoni effects are compared to one another. For a water–ethanol mixture of 10wt.% ethanol, it appears that the solutal Marangoni effect is by far the most important instability mechanism. Furthermore, its global action can be described within a Pearson-like model, with an appropriately defined Biot number depending on the wavenumber. On the other hand, it is also shown that, if taken into account, water evaporation has only minor quantitative consequences upon the results for this predominant, solutal Marangoni mechanism.
Keywords: Stability analysis; Binary mixture; Evaporation; Rayleigh; Marangoni; Solutal and thermal effects
Characterization of the wettability of thin nanostructured films in the presence of evaporation
by Anita Rogacs; Julie E. Steinbrenner; Jeremy A. Rowlette; Jeffrey M. Weisse; Xiaolin L. Zheng; Kenneth E. Goodson (pp. 354-360).
Pore level contact angle, evaporation rate, and fluid-independent structural constant of a VLS grown SiNW array were determined using a low-cost, non-contact optical tracking methodology.Display Omitted► Neglecting evaporation effects in wettability characterization of porous thin films can lead to significant errors. ► Proposed model accounts for evaporation in addition to capillary pressure and viscous force. ► Internal contact angle of a disordered silicon nanowire film is extracted from optical imaging measurements.Vapor chambers using conventional porous membrane wicks offer limited heat transfer rates for a given thickness. This limitation can be addressed through wick nanostructuring, which promises high capillary pressures and precise control of the local porosity. This work develops a measurement technique for the wettability of nanostructured wicks based on optical imaging. Feasibility is demonstrated on a hydrophilic silicon nanowire array (SiNW) synthesized using the Vapor–Liquid–Solid (VLS) growth mechanism followed by surface plasma treatment. The wettability is determined by comparing the time-dependent liquid interface rise with a model that accounts for capillary, viscous, and gravitational forces and for evaporation. This model is demonstrated to be useful in extracting internal contact angle from thin (∼10μm) porous films.
Keywords: Internal contact angle; Wettability; Nanostructured wick; Evaporation; Silicon nanowire array
Polymer/silica composite of core–shell type by polymer swelling in TEOS
by Agnieszka Kierys; Marek Dziadosz; Jacek Goworek (pp. 361-365).
Silica microfibers anchored in a polymer bead.Monodisperse polymer/silica composite material with a polymer as the core and hydrophilic silica gel as the shell was prepared by a two-stage procedure. In the first stage, the swelling of Amberlite XAD7HP particles in tetraethoxysilane (TEOS) was performed. Subsequently a portion of the XAD7HP particles impregnated with TEOS were transferred to acidic aqueous solution to facilitate a sol–gel process of the silica precursor. This procedure is assessed as a potential route to a composite material with a core–shell morphology. Scanning electron microscopy and29Si MAS NMR indicated the formation of silica microfibers on polymer beads. The silica microfibers were anchored in the polymer matrix. In consequence, the silica shell exhibited relatively high mechanical stability. The swelling of the polymer and the formation of the silica phase substantially changed the porosity of the initial polymer material. The final composite surprisingly exhibited very homogeneous porosity. The textural characteristics of the investigated materials were defined by nitrogen adsorption–desorption at 77K.
Keywords: Polymer–silica composite; Polymer swelling; Mesoporous materials; Synthesis
Hydrostatic meniscus between two eccentric circular cylinders
by C. Pozrikidis (pp. 366-373).
Meniscus between two eccentric cylinders for inner to outer cylinder radii ratio a2/ a1=0.4 and inner cylinder center offset d/ a1=0.5.A numerical method is implemented for computing the shape of a three-dimensional hydrostatic meniscus extending between two arbitrary closed contact lines under the restriction that the projections of the contact lines in a horizontal plane are eccentric circles. In a physical realization, the contact lines are attached to vertical circular cylinders, spherical particles or containers. The Laplace–Young equation determining the meniscus shape is solved in bipolar coordinates generated by conformal mapping using a finite-difference method, and the capillary force and torque exerted on the cylinders are evaluated. Numerical results are presented for a meniscus extending between two circular horizontal contact lines. The horizontal component of the capillary force at each contact line is found to increase monotonically with the cylinder center offset, favoring the concentric configuration.
Keywords: Hydrostatics; Meniscus; Laplace–Young equation
Behavior of cationic surfactants and short chain alcohols in mixed surface layers at water–air and polymer–water interfaces with regard to polymer wettability. I. Adsorption at water–air interface
by Anna Zdziennicka; Bronisław Jańczuk (pp. 374-383).
Mutual influence of cetyltrimethylammonium bromide (CTAB) concentration ( C1) and alcohol activity on adsorption at water–air interface.Measurements of the surface tension of aqueous solutions were carried out at 293K for mixtures of cetyltrimethylammonium bromide (CTAB) with short chain alcohols such as methanol and ethanol, as well as for 1-hexadecylpyridinium bromide (CPyB) with the same alcohols. The concentration of CTAB and CPyB in aqueous solutions was in the range from 10−5 to 10−3 M, and methanol and ethanol was in the range from 0 to 21.1M and from 0 to 11.97M, respectively. Moreover, the surface tension of aqueous solution mixtures of cationic surfactants with propanol in the concentration range from 0 to 6.67M was also taken into consideration. The obtained isotherms of the surface tension were compared to those calculated from the Szyszkowski and Connors equations. The constants in these equations were determined by the least squares method. It appeared that they depended on the type of surfactant and alcohol. From comparison of the experimental and theoretical isotherms of the surface tension it is possible, at first approximation, to describe the relationship between the surface tension of aqueous solutions of cationic surfactants with short chain alcohol mixtures as a function of alcohol molar fraction in the bulk phase by the Szyszkowski and Connors equations. Furthermore, changes of the surface tension of aqueous solutions of CTAB and CPyB with alcohol mixtures at each constant concentration of cationic surfactant can be predicted by the Fainerman and Miller equation, if it is possible to determine the molar area of cationic surfactant and alcohol in the mixed monolayer. Based on the surface tension isotherms the Gibbs surface excess concentration of cationic surfactants and alcohols at water–air interface was determined, and in the case of alcohol, this concentration excess was recalculated for that of Guggenheim-Adam. The Guggenheim-Adam surface excess concentration was applied for determination of the real concentration of alcohol in the mixed surface monolayer. The real concentration of cationic surfactant was assumed equal to Gibbs surface excess concentration. For determination of the composition of the surface layer, its proper thickness was assumed. The composition of the surface mixed monolayer was discussed with regard to the standard free energy of cationic surfactant and alcohol adsorption at water–air interface determined in different ways. The standard free energy of adsorption of “pure” cationic surfactants determined from the Langmuir and Aronson and Rosen equations was compared to that deduced on the basis of Cp20, and the surface tension of the cationic surfactant tail and tail–water interface tension.
Keywords: Cationic surfactants; Short chain alcohols; Adsorption; Surface layer composition; Standard free energy of adsorption
NMR measurement of the transport dynamics of colloidal particles in an open cell polymer foam porous media
by Tyler R. Brosten; Einar O. Fridjonsson; Sarah L. Codd; Joseph D. Seymour (pp. 384-391).
The transport of model hard sphere core shell colloidal particles under flow through a random open-cell solid polymer foam is studied using nuclear magnetic resonance. Unique data on the scale dependent dynamics of the colloidal particle and suspending fluid phase are obtained using spectral chemical resolution. The dynamics of each phase are shown to differ from one another dependent on the displacement length and time scale of the measurement. The data is interpreted in the context of classic hydrodynamic dispersion theory and mechanisms of transport for each phase.The transport of model hard sphere core shell colloidal particles under flow through a random open-cell solid polymer foam is studied using nuclear magnetic resonance. Unique data on the scale dependent dynamics of the colloidal particle and suspending fluid phase are obtained using spectral chemical resolution. The dynamics of each phase are shown to differ from one another dependent on the displacement length and time scale of the measurement. The data is interpreted in the context of classic hydrodynamic dispersion theory and mechanisms of transport for each phase.
Keywords: Colloid transport; Hydrodynamic dispersion; Magnetic resonance
Preparation of uniform monomer droplets using packed column and continuous polymerization in tube reactor
by Masahiro Yasuda; Takashi Goda; Hiroyasu Ogino; Wilhelm Robert Glomm; Hiroaki Takayanagi (pp. 392-401).
Emulsification technique using glass bead-packed column is useful for the continuous production of uniform monomer emulsion droplets.A two-step continuous emulsification and polymerization process was developed in which monomer droplets having narrow size distribution were prepared and polymerized while retaining their monodispersity. In the emulsification step, a column packed with glass beads, of diameters ranging from 70μm to 1mm, was used to prepare a monomer O/W emulsion. Monomer droplets were dispersed with an aqueous solution of poly(vinyl alcohol) (PVA). The droplet size and -distribution was studied with respect to the effects of diameter of glass beads, concentration of PVA in water phase, degree of polymerization of PVA, ratio of mass flow of water phase to that of oil phase, linear velocity of water phase and viscosity of water phase and oil phase. Droplet size was found to be strongly dependent on the diameter of the packed glass beads, while the droplet size distribution was affected by the viscosities of the continuous and dispersed phases. Increasing the viscosity of the dispersed phase by addition of poly(styrene) to the monomer mixture resulted in a narrow size distribution of glycidyl methacrylate–ethylene glycol dimethacrylate droplets. Furthermore, these initiator-containing monomer droplets were polymerized by heating in a tubular reactor, from which polymer particles with a narrow size distribution could be synthesized.
Keywords: Suspension polymerization; Glass beads packed column; Monomer droplet; Narrow droplet size distribution; Continuous tube reactor
Synthesis of Fe metal precipitated colloidal silica and its application to W chemical mechanical polishing (CMP) slurry
by Young-Jae Kang; Y. Nagendra Prasad; In-Kwon Kim; Seok-Jo Jung; Jin-Goo Park (pp. 402-407).
Precipitation of Fe metal ions on colloidal silica particle for the application of W CMP process.The objective of this paper is to develop a new method of Fe (metal) precipitation on colloidal silica to overcome the stability problem, which would be responsible in producing defects, with commercially available fumed silica slurry containing Fe ions. The slurry was developed by using sodium silicate (Na2SiO3) as a raw material and the concentration of precipitation of metal was controlled by addition of Fe salt (Fe(NO3)3). To compare the concentration of precipitated Fe with directly added Fe ions in slurry solutions, static electrochemical and peroxide decomposition experiments were performed. Although the performance of the Fe precipitation appeared to be lower than Fe ion addition during these experiments, nearly equal removal rate was observed due to the dynamic condition during polishing. The Fe precipitated colloidal silica particles at the concentration of 52ppm showed the similar W removal rate and selectivity of W to TEOS (tetraethylorthosilicate) to commercially available fumed silica slurry containing externally added Fe ions. The introduction of Fe particle precipitation on colloidal silica particles would result in a longer shelf life time and hence lower defect level in W CMP.
Keywords: W CMP; Fe precipitation on colloidal silica; Slurry stability; Removal rate; Selectivity
Evolution of volume fractions and droplet sizes by analysis of electrical conductance curves during destabilization of oil-in-water emulsions
by M. Kostoglou; E.-M. Varka; E.P. Kalogianni; T.D. Karapantsios (pp. 408-416).
A continuous non-intrusive electrical conductance technique delivers local volume fractions and droplet sizes during emulsion destabilization. The electrically determined droplet sizes are compared to microscopy data.Destabilization of hexane-in-water emulsions is studied by a continuous, non-intrusive, multi-probe, electrical conductance technique. Emulsions made of different oil fractions and surfactant (C10E5) concentrations are prepared in a stirred vessel using a Rushton turbine to break and agitate droplets. During the separation of phases, electrical signals from pairs of ring electrodes mounted at different heights onto the vessel wall, are recorded. The evolution of the local water volume fractions at the locations of the electrodes is estimated from these signals. It is found that in the absence of coalescence, the water fraction evolution curve from the bottom pair of electrodes is compatible with a bidisperse oil droplet size distribution. The sizes and volume fractions of the two droplet modes are estimated using theoretical arguments. The electrically determined droplet sizes are compared to data from microscopy image analysis. Results are discussed in detail.
Keywords: Emulsions; Destabilization; Electrical conductance technique; Droplet size distribution; Droplet motion
Streaming potential generated by two-phase flow in a polygonal capillary
by J.D. Sherwood; Etienne Lac (pp. 417-423).
The streaming potential generated by fluid motion in a polygonal capillary is modified by the presence of a non-conducting drop of oil. The oil drop changes both the shear rate at the wall, and the electrical conductance of the capillary.Theoretical predictions of the streaming potential generated by two-phase flow in a polygonal capillary are presented. The capillary walls are wetted by the continuous water phase, in which is suspended a long non-conducting oil drop. It is assumed that when fluid flows along the capillary a thin film of fluid is created between the drop and the capillary walls, which allows ions in the charge cloud adjacent to the wall to be convected. Current returns via conduction along the menisci of wetting fluid in the corners of the polygonal capillary. These menisci have finite cross-sectional area even when fluid is at rest, so that streaming potentials are predicted to grow linearly with the applied pressure gradient.
Keywords: Electrical double layer; Two-phase flow; Streaming potential
A comparative study on different ionic liquids used as surfactants: Effect on thermal and mechanical properties of high-density polyethylene nanocomposites
by Sébastien Livi; Jannick Duchet-Rumeau; Thi-Nhàn Pham; Jean-François Gérard (pp. 424-433).
Phosphonium and imidazolium ionic liquids: thermostable surfactants for layered silicate modification.Dialkyl imidazolium and alkyl phosphonium salts were synthesized to be used as new surfactants for cationic exchange of layered silicates, such as montmorillonite (MMT). The synthesized phosphonium (P-MMT) or imidazolium ion (I-MMT)-modified montmorillonites display a dramatically improved thermal degradation with respect to commonly used quaternary ammonium salts. This thermal degradation window can still be shifted toward higher temperatures after washing of modified clays. Two kinds of organic species can be identified onto clay: physically adsorbed species versus chemically adsorbed species. To evidence the impact of these thermally resistant ionic liquids, the modified montmorillonites were introduced in a great commodity polymer, i.e., high-density polyethylene. Thermoplastic nanocomposites with a very low amount of nanofillers were processed in melt by twin screw extrusion. If the thermal stability of polyethylene is slightly increased with only 2wt.% of thermostable made clays, the stiffness–toughness compromise is well improved since a strong increase in modulus is achieved with both thermostable clays without loss of fracture properties. But these mechanical performances are mainly obtained with unwashed thermostable clays because the physically adsorbed organic species onto clay surfaces behave like a compatibilizer that helps both the dispersion into the PE matrix and improves the clay/matrix interface quality.
Keywords: Ionic liquid; Montmorillonite; Cationic exchange; Thermal stability; Polyethylene; Nanocomposite
Thermo-physical property measurement of nano-gold dispersed water based nanofluids prepared by chemical precipitation technique
by G. Paul; T. Pal; I. Manna (pp. 434-437).
The thermal conductivity ( k) enhancement of gold–water nanofluids measured as a function of volume fraction shows a significant increase (∼48%) well beyond the level predicted by conventional theories.Nano-gold dispersed water based nanofluid has been prepared following the chemical reduction method. Crystallite size, particle size/shape/morphology, and purity of the nanoparticles have been characterized using X-ray diffraction, scanning and transmission electron microscopy and energy dispersion spectroscopy, respectively. The degree of thermal conductivity enhancement of the nanofluid (with respect to the base fluid) as a function of concentration and size of gold nanoparticle has been determined using the transient hot-wire technique. The degree of enhancement increases with increase in concentration and decrease in size of nanoparticles. The maximum enhancement recorded is ∼48% at 0.00026vol.% concentration and 21nm average particle size.
Keywords: Nanofluid; Gold; Particle size; Particle concentration; Transient hot-wire method
Numerical analysis for the thermophoretic coagulation of monodisperse particles at continuum regime
by Haesung Jung; Sun Young Lee; Jung Hyeun Kim (pp. 438-441).
Thermophoretic coagulation is more effective for higher temperature gradient in the monodisperse aerosol particles when particles induce thermophoretic force.Coagulation is a process wherein aerosol particles collide with one another and adhere to form large particles in the system due to their relative motions. In this letter, we investigated thermophoretic coagulation of monodisperse aerosols on a constant temperature gradient between particles and gas molecules using a FDM (finite difference method) technique. The basic concept is to focus on a single particle attracting other particles considering their diffusional and thermophoretic motions to its collision surface. From the results of simulated particle flux, it shows that the thermophoretic coagulation is more effective for higher temperature gradient in the monodisperse aerosol particles.
Keywords: Thermophoresis; Coagulation; FDM; Continuum regime; Particle interaction; Monodisperse particle
Simulation-assisted evidence for the existence of two stable kaolinite/potassium acetate intercalate complexes
by Éva Makó; Gábor Rutkai; Tamás Kristóf (pp. 442-445).
Kaolinite/potassium acetate intercalate complexes were examined by XRD and molecular simulation. An additional stable basal spacing was found besides the well-known one.Recent molecular simulation findings with several kaolinite intercalate complexes raised the question of the existence of more than one stable state, which has not been confirmed by experimental observations yet. Kaolinite/potassium acetate intercalate complexes were synthesized and examined by X-ray diffraction, and a molecular simulation study was performed for the system. Consistent with the suggestion from the simulations, an additional stable basal spacing was found experimentally at d001=1.168nm besides the well-known one at d001=1.403nm.
Keywords: Kaolinite; Intercalation; Potassium acetate; X-ray diffraction; Molecular simulation
Electrokinetic energy conversion in microchannels using polymer solutions
by Claudio L.A. Berli (pp. 446-448).
Schematic illustration of an elementary electrokinetic generator, where the working fluid is a polymer solution that presents wall depletion.Electrokinetic energy conversion in microfluidic systems is a subject of intense research at present, where the main objective is to improve the thermodynamic efficiency of the process. As a novel strategy to the problem, this work focuses on the fluid dynamic properties of the working fluid. It is shown that polymer solutions with wall depletion can substantially increase the conversion efficiency in comparison to simple electrolytes under the same operating conditions. The effect is given by a reduction of the hydrodynamic conductance, while the streaming current is unaltered. It is also found that the maximum efficiency of electrokinetic power generation differs from that of electroosmotic pumping, in contrast to the case of simple electrolytes. This is due to the non-Newtonian character of polymeric fluids, which leads to nonlinear electrokinetic relations.
Keywords: Energy conversion; Microfluidics; Polymeric fluids; Nonlinear electrokinetics