Journal of Colloid And Interface Science (v.364, #1)
Highly transparent and conductive thin films fabricated with nano-silver/double-walled carbon nanotube composites
by Shie-Heng Lee; Chih-Chun Teng; Chen-Chi M. Ma; Ikai Wang (pp. 1-9).
The basic methodology of immobilizing silver nanoparticles on DWNTs surfaces through amidation. (A) Oxidizing DWNTs with the mixture of acids, (B) modifying the silver surface with NH2(CH2)2SH, and (C) amide-forming reaction.Display Omitted► Silver nanoparticles grafts on the CNT surface improve its conductivity of CNT thin film. ► Silver nanoparticle grafts on the CNT by surface condensation reaction. ► Higher transmittance and lower sheet resistance transparent conductive film. ► Easy process for commercial production. ► It could be applied in flexible electronic devices.This study develops a technique for enhancing the electrical conductivity and optical transmittance of transparent double-walled carbon nanotube (DWNT) film. Silver nanoparticles were modified with a NH2(CH2)2SH self-assembled monolayer terminated by amino groups and subsequent surface condensation that reacted with functionalized DWNTs. Ag nanoparticles were grafted on the surface of the DWNTs. The low sheet resistance of the resulting thin conductive film on a polyethylene terephthalate (PET) substrate was due to the increased contact areas between DWNTs and work function by grafting Ag nanoparticles on the DWNT surfaces. Increasing the contact area between DWNTs and work function improved the conductivity of the DWNT-Ag thin films. The prepared DWNT-Ag thin films had a sheet resistance of 53.4Ω/sq with 90.5% optical transmittance at a 550nm wavelength. After treatment with HNO3 and annealing at 150°C for 30min, a lower sheet resistance of 45.8Ω/sq and a higher transmittance of 90.4% could be attained. The value of the DC conductivity to optical conductivity ( σDC/ σOP) ratio is 121.3.
Keywords: Carbon nanotube; Transparent conductive film; Electrical resistance; Flexible; Nano-silver
Morphology driven ultraviolet photosensitivity in ZnO–CdS composite
by Shrabani Panigrahi; Durga Basak (pp. 10-17).
Different charge transfer process at the interface due to difference in morphology of ZnO causes a contrast change in the UV sensitivity properties of ZnO–CdS composite.Display Omitted► Two forms of ZnO–CdS based nanocomposites have been designed. ► The change in the UV photosensitivity depends on the morphology of the composite. ► Interfacial charge transfer process is dependent on the morphology.Semiconductors in the form of composite yields immense possibilities for the study of charge transfer processes at the interface. We have designed CdS nanoparticles (NPs) capped ZnO nanostructures using two morphologies of the latter namely nanorods arrays (NRAs) and nanocrystalline film to form a composite NRAs and composite films respectively. The photocurrent values in both the composites have been increased but to a different extent when these are illuminated with the ultraviolet (UV) light. More interestingly, the resultant UV photosensitivity in the composite NRAs is decreased while that in the composite films is increased as compared to the values of the respective uncapped samples. A different charge transfer process at the interface is occurred due to the difference in the morphologies resulting in a contrast change in the UV sensitivity. The photoluminescence results also show that the change in the emission property is morphology-dependent. Therefore, our results imply that the choice of the morphology while making a nanocomposite is crucial to tune its UV sensitivity as well as optical properties.
Keywords: Surface capping; Nanocomposite; UV sensitivity; CdS; ZnO
Introduction of a planar defect in a molecularly imprinted photonic crystal sensor for the detection of bisphenol A
by Nébéwia Griffete; Hugo Frederich; Agnès Maître; Catherine Schwob; Serge Ravaine; Benjamin Carbonnier; Mohamed M. Chehimi; Claire Mangeney (pp. 18-23).
We use the Langmuir–Blodgett technique to introduce a planar defect layer within an inverse opal hydrogel made of a molecularly imprinted polymer. The resulting defect-embedded imprinted photonic polymer offers improved bisphenol A sensing capacities as compared to the defect-free structure, opening new opportunities for the design of label-free real-time sensing materials.Display Omitted► A planar defect was introduced in a molecularly imprinted photonic crystal sensor. ► The inverse opal structure was sensitive to the presence of bisphenol A. ► The defect layer was shown to enhance the sensitivity of the photonic crystal.This paper reports the preparation of a molecularly imprinted inverse opal hydrogel containing a 2D defect layer, by combining the Langmuir–Blodgett technique and the photonic crystal template method. By coupling the exceptional characteristics of molecularly imprinted polymers, sensitive to the presence of a target molecule, and those of photonic crystals in a single device, we could obtain a defect-embedded imprinted photonic polymer consisting in a three-dimensional, highly-ordered and interconnected macroporous array, where nanocavities complementary to analytes in shape and binding sites are distributed. As a proof of concept, we prepared a three-dimensional macroporous array of poly(methacrylic acid) (PMAA) containing molecular imprints of bisphenol A (BPA) and a planar defect layer consisting in macropores of different size. The optical properties of the resulting inverse opal were investigated using reflection spectroscopy. The defect layer was shown to enhance the sensitivity of the photonic crystal material, opening new possibilities towards the development smart optical sensing devices.
Keywords: Photonic crystal; Defect layer; Molecularly imprinted polymers; Optical properties; Bisphenol A
Preparation of bi-functional silica particles for antibacterial and self cleaning surfaces
by Neha Y. Hebalkar; Snigdhatanu Acharya; Tata N. Rao (pp. 24-30).
Schematic illustration of silica@TiO2, Ag core–shell particle formation and their bifunctional activity.Display Omitted► Bifunctional silica with ultra fine titania and silver nanoparticles on its surface. ► Formation of silica@titania,silver core shell structure. ► Titania and silver enhance photocatalytic and antibacterial activity together. ► White colored composite due to ultra small nano silver size. ► Technologically important material which retains original colour of the substrate.Synthesis of bi-functional silica particles by a simple wet chemical method is described where the mixture of ultra fine nanoparticles (1–3nm) of titania and silver were attached on the silica particle surface in a controlled way to form a core–shell structure. The silica surface showed efficient bi-functional activity of photo-catalytically self cleaning and antibacterial activity due to nanotitania and nanosilver mutually benefiting each other’s function. The optimum silver concentration was found where extremely small silver nanoparticles are formed and the total composite particle remains white in color. This is an important property in view of certain applications such as antibacterial textiles where the original fabric color has to be retained even after applying the nanosilver on it. The particles were characterized at each step of the synthesis by X-ray photoelectron spectroscopy, UV–visible spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron energy loss spectroscopy. Bi-functional silica particles showed accelerated photocatalytic degradation of methylene blue as well as enhanced antibacterial property when tested as such particles and textiles coated with these bi-functional silica particles even at lower silver concentration.
Keywords: Core–shell; Bi-functional; Silver; Titania; Antibacterial; Self-cleaning
Polymer-hybridized liposomes anchored with alkyl grafted poly(asparagine)
by Sung-Il Park; Eun-Ok Lee; Jin Woong Kim; Youn Joon Kim; Sang Hoon Han; Jong-Duk Kim (pp. 31-38).
Polymer-hybridized liposomes (PHLs) of saturated lecithin were formed by association of poly(asparagines) grafted with alkyl chains. The membrane properties of the PHLs were varied with alkyl chain length of polymer.Display Omitted► The membrane fluidity of liposomes increases by the inclusion of the alkyl grafted poly(asparagines). ► The membrane rigidity of polymer-hybridized liposomes increases with the alkyl chain length of polymer. ► The anchored polymer induces a shift in Tc of the lipid bilayer. ► The number of polymer–lipid mixed micelles increases with polymer concentration.Polymer-hybridized liposomes (PHLs) of saturated lecithin were formed by association of poly(asparagines) grafted with alkyl chains (PAsn-g-Cn). The thermal, physical, and surface properties of the polymer-hybridized liposomes were examined with varying polymer concentration, alkyl chain length (C8, C12, C18, C22), and degree of substitution (DS) in the polymer. The inclusion of the polymer raised the membrane fluidity of liposomes. By the incorporation of small amount of polymer, the membrane rigidity of liposomes dropped sharply and then increased close to the original level as the polymer concentrations increased in the cases of PAsn-g-C18 and PAsn-g-C22. Also, the membrane rigidity and stability of PHLs increased with alkyl chain length at the same polymer concentration. The surface charge of PHL associated with PAsn-g-C22 was changed by DS of alkyl chains. The polymer bearing long alkyl chains (C12, C18, C22) formed PHLs well at low polymer concentration and the number of disk-shaped polymer–lipid mixed micelles increased with polymer concentration. The anchored polymers induced shifts in gel-to-liquid crystal transition temperature (Tc) of the vesicles and Tc varied with polymer concentration, alkyl chain length, and DS of the polymer.
Keywords: Polymer hybridized liposome; Poly(asparagine); Alkyl chain length; Vesicle structure; Membrane fluidity
High density silver nanoparticle monolayers produced by colloid self-assembly on polyelectrolyte supporting layers
by Magdalena Oćwieja; Zbigniew Adamczyk; Maria Morga; Aneta Michna (pp. 39-48).
A method of producing high-density silver particle monolayer was developed.Display Omitted► Formation of high density monolayers of silver particle on polyelectrolyte covered mica by the self-assembling. ► The density of silver monolayers can be controlled and designed by changing the ionic strength. ► Efficient method of determining particle size of in bulk was proposed. ► Silver monolayer may find practical applications as antibacterial coatings, in various SERS techniques and in catalysis.A stable silver nanoparticle suspension was synthesized via the reduction of silver nitrate using sodium borohydride and sodium citrate. The particle’s shape and size distribution were measured by various methods. The electrophoretic mobility measurements revealed that the zeta potential of particles was highly negative, increasing slightly with the ionic strength, from −52mV for I=10–5 M to −35mV for I=3×10−2M (for pH=5.5). The zeta potential of mica modified by the adsorption of cationic polyelectrolytes: PEI and PAH was also determined using the streaming potential measurements. The modified mica sheets were used as substrates for particle monolayers formed via colloid self assembly. The kinetics of this process, proceeding under diffusion-controlled transport conditions, was quantitatively evaluated by a direct enumeration of particles using the AFM and SEM techniques. Both the kinetics of particle deposition and the maximum surface concentration were determined. From the slope of the initial deposition rates, the equivalent diameter of particles was determined to be 16nm, in agreement with previous measurements. Based on this finding, an efficient method of determining particle size in suspension was proposed. It was also demonstrated that for higher ionic strengths, the maximum coverage of particle monolayers on PAH modified mica exceeded 0.39. The kinetic data were quantitatively interpreted in terms of the random sequential adsorption (RSA) model using the effective hard particle concept.
Keywords: Deposition of silver particles; Kinetics of silver particle deposition; Monolayers of silver particles; Silver nanoparticles; Synthesis of silver sol
Effect of γ-irradiation on the growth of ZnO nanorod films for photocatalytic disinfection of contaminated water
by Julio Alarcón; Silvia Ponce; Francisco Paraguay-Delgado; Juan Rodríguez (pp. 49-55).
Nanorod films fabricated onto γ-irradiated seeds showing crystalline texture. Inset shows a micrograph of the best textured film.Display Omitted► ZnO seed films with surface roughness and morphology influenced by γ-irradiation. ► ZnO nanorod films with morphology and texture influenced by γ-irradiation. ► Textured ZnO nanorod films improve the photocatalytic bacteria degradation.The growth of ZnO nanorods on a flat substrate containing γ-irradiated seeds and their ability to photocatalytically eliminate bacteria in water were studied. The seed layer was obtained, by the spray pyrolysis technique, from zinc acetate solutions γ-irradiated within the range from 0 to 100kGy. Subsequently, to grow the rods, the seeds were immersed in a basic solution of zinc nitrate maintained at 90°C. The rate of crystal growth on the seed layer during the thermal bath treatment was kept constant.The resulting materials were characterized morphologically by scanning electron and atomic force microscopies; X-ray diffraction was used to study their morphology and structure and ultraviolet–visible spectroscopy to determine their absorbance. The obtained seed films were morphologically dependent on the radiation dose and this was correlated with the ZnO nanorod films which presented a texture in the (002) direction perpendicular to the substrate. The rods have a hexagonal mean cross section between 20 and 140nm. Using these rods, the photocatalytic degradation of Escherichia coli bacteria in water was studied; a positive influence of the crystalline texture on the degradation rate was observed.
Keywords: ZnO; Nanorods; Films; Seeds; Spray pyrolysis; γ-Radiation; Photocatalysis; Water disinfection; E. coli
Uniform-sized silicone oil microemulsions: Preparation, investigation of stability and deposition on hair surface
by Habiba Nazir; Piping Lv; Lianyan Wang; Guoping Lian; Shiping Zhu; Guanghui Ma (pp. 56-64).
Uniform-sized silicone oil microemulsions with different droplet diameters were successfully prepared using membrane emulsification technique in comparison with conventional homogenizer. Size and uniformity of silicone oil droplets have important influence on the deposition property of hair surface.Display Omitted► ME technique is promising to prepare uniform-sized silicone oil emulsions. ► Droplet size and uniformity have important effect on silicone oil deposition on hair. ► Size distribution is vital to control emulsion stability, deposition and hair friction. ► Alginate plays a significant role to enhance the silicone oil deposition on hair.Emulsions are commonly used in foods, pharmaceuticals and home-personal-care products. For emulsion based products, it is highly desirable to control the droplet size distribution to improve storage stability, appearance and in-use property. We report preparation of uniform-sized silicone oil microemulsions with different droplets diameters (1.4–40.0μm) using SPG membrane emulsification technique. These microemulsions were then added into model shampoos and conditioners to investigate the effects of size, uniformity, and storage stability on silicone oil deposition on hair surface. We observed much improved storage stability of uniform-sized microemulsions when the droplets diameter was ⩽22.7μm. The uniform-sized microemulsion of 40.0μm was less stable but still more stable than non-uniform sized microemulsions prepared by conventional homogenizer. The results clearly indicated that uniform-sized droplets enhanced the deposition of silicone oil on hair and deposition increased with decreasing droplet size. Hair switches washed with small uniform-sized droplets had lower values of coefficient of friction compared with those washed with larger uniform and non-uniform droplets. Moreover the addition of alginate thickener in the shampoos and conditioners further enhanced the deposition of silicone oil on hair. The good correlation between silicone oil droplets stability, deposition on hair and resultant friction of hair support that droplet size and uniformity are important factors for controlling the stability and deposition property of emulsion based products such as shampoo and conditioner.
Keywords: Silicone oil; Membrane emulsification technique; Emulsions; Uniform size; Deposition
Size tuning of luminescent silicon nanoparticles with meso-porous silicon membranes
by T. Serdiuk; V. Lysenko; S. Alekseev; V.A. Skryshevsky (pp. 65-70).
PL spectra with corresponding photos of initial and filtered ethanol solutions with dispersed Si NPs.Display Omitted► Meso-porous Si membranes was shown as efficient tool for nanoparticle (NP) size tuning. ► SBS filtration are most precise method for carry size selection of Si NPs. ► SBS filtration allows to find full discrete set of photoluminescence peaks. ► Quantum of step-like NP size increasing equal to 0.12nm is observed.Size tuning of silicon (Si) nanoparticles (NPs) with the use of meso-porous silicon (meso-PS) free-standing layers is reported for the first time. Accumulation of Si NPs inside the membrane pores during the filtering process (NP transport through the meso-PS) leads to an auto-filtration effect (called Si-by-Si (SBS) filtration) allowing more efficient size selection of the NPs. General complex fractal shape and surface chemistry of the whole porous network, layer thickness as well as a given initial NP size dispersion determine final size of the NPs in the filtered solution. Moreover, quantum of step-like NP size increasing equal to 0.12nm was found.
Keywords: Si nanoparticles; Meso-porous Si; Auto-filtration; Size selection; Photoluminescence; Size tuning; Free-standing Si membranes
Improving the heat transfer efficiency of synthetic oil with silica nanoparticles
by Elena V. Timofeeva; Michael R. Moravek; Dileep Singh (pp. 71-79).
The heat transfer efficiency (hnf/h 0) of formulated SiO2 suspensions increases with particle concentration and provides higher benefits when nanofluids are used in laminar flow regime or at higher temperatures in turbulent flow regime.Display Omitted► Stable suspensions of SiO2/Therminol 66 are formulated with cationic surfactant. ► The viscosity and thermal conductivity depend on the agglomerate sizes. ► Agglomerate sizes are controlled by surfactant-to-nanoparticle ratio and temperature. ► Nanofluid shows enhanced heat transfer at all temperatures in a laminar flow. ► In a turbulent flow nanofluid beneficial only at elevated temperatures.The heat transfer properties of synthetic oil (Therminol 66) used for high temperature applications was improved by introducing 15nm silicon dioxide nanoparticles. Stable suspensions of inorganic nanoparticles in the non-polar fluid were prepared using a cationic surfactant (benzalkonium chloride). The effects of nanoparticle and surfactant concentrations on thermo-physical properties (viscosity, thermal conductivity and total heat absorption) of these nanofluids were investigated in a wide temperature range. The surfactant-to-nanoparticle (SN) ratio was optimized for higher thermal conductivity and lower viscosity, which are both critical for the efficiency of heat transfer. The rheological behavior of SiO2/TH66 nanofluids was correlated to average agglomerate sizes, which were shown to vary with SN ratio and temperature. The conditions of ultrasonic treatment were studied and the temporary decrease of agglomerate size from an equilibrium size (characteristic to SN ratio) was demonstrated. The heat transfer efficiencies were estimated for the formulated nanofluids for both turbulent and laminar flow regimes and were compared to the performance of the base fluid.
Keywords: Heat transfer fluid; Synthetic oil; Therminol; Nanofluid; Silica; Silicon oxide; Nanoparticles; Surfactant; Thermal conductivity; Viscosity; Total heat; Heat transfer efficiency; Cationic surfactant; Benzalkonium chloride
Chitosan and silver nanoparticles as pudding with raisins with antimicrobial properties
by M. Carmen Rodríguez-Argüelles; Carmen Sieiro; Roberto Cao; Lucia Nasi (pp. 80-84).
Chitosan nanoparticles (78nm) containing small silver nanoparticles (0.93–1.7nm) as a pudding with raisins with interesting antimicrobial activity are reported.Display Omitted► Silver nanoparticles included in chitosan nanoparticles. ► Green way to obtain AgNP. ► Relatively small size of CS-NP (78nm). ► Very small AgNP (<2nm).Chitosan nanoparticles (CS-NP) containing small silver nanoparticles are reported (Ag@CS-NP). CS-NP was synthesized using tripolyphosphate (TPP) as a polyanionic template. TPP also served to electrostatically attract Ag+ inside CS-NP, where it was reduced by the terminal glucosamine units of the biopolymer. This procedure is environmental friendly, inexpensive, and permits the synthesis of very small AgNP (0.93–1.7nm), with only a discrete dependence from the amount of silver nitrate used (5–200mg). The obtained hybrid nanocomposites Ag@CS-NP were characterized by DLS, HRTEM, and HAADF–STEM presenting a mean hydrodynamic diameter of 78nm. The antimicrobial activity of Ag@CS-NP against Candida glabrata, Sacharomyces cerevisiae, Escherichia coli, Klebsiella pneumoniae, Salmonella, Staphylococcus aureus, and Bacillus cereus corresponded to MIC values lower than for AgNO3.
Keywords: Antimicrobial; Chitosan; Nanoparticle; Nanocomposite; Silver; TEM
Synthesis of transparent aqueous sols of colloidal layered niobate nanocrystals at room temperature
by Takayuki Ban; Shogo Yoshikawa; Yutaka Ohya (pp. 85-91).
The colloidal tetramethylammonium niobate nanocrystals in the synthesized transparent aqueous sols were about 4 nm in size and had a crystal structure similar to layered hexaniobate.Display Omitted► Highly water-dispersible niobate nanocrystals were synthesized at room temperature. ► The niobate nanocrystals were similar in crystal structure to M4Nb6O17· nH2O. ► Oriented niobium oxide films were fabricated from the niobate colloidal solution by the sol–gel method. ► The orientation of the Nb2O5 films was attributed to the layered structure of the niobate.Transparent aqueous sols of colloidal tetramethylammonium niobate nanocrystals were synthesized by mixing tetramethylammonium hydroxide (TMAOH), niobium ethoxide, and water at TMAOH/Nb⩾0.7 at room temperature. The X-ray diffraction patterns of the thin films prepared by evaporating the colloidal solutions on a glass substrate indicated that the colloidal niobate had a layered crystalline structure. Two types of layered structures are known as a layered niobate, i.e. M4Nb6O17· nH2O and MNb3O8 (M=H, H3O, or alkaline metal). Raman spectra and electron diffraction suggested that the niobate nanocrystals were similar in crystal structure to M4Nb6O17· nH2O compounds. Moreover, when niobium oxide thin films were fabricated from the niobate colloidal solutions by the sol–gel method, oriented T-Nb2O5 thin films, whose c-axis was parallel to the substrate surface, were obtained. The orientation of the thin films was probably attributed to the layered structure of the colloidal niobate nanocrystals.
Keywords: Layered niobates; Solution process; Colloidal solution; Nanocrystal
Self-assembly of pH-sensitive mixed micelles based on linear and star copolymers for drug delivery
by Xiujuan Huang; Yan Xiao; Meidong Lang (pp. 92-99).
The mixed micelles constructed from the star and linear copolymers were transformed from a core–shell structure into a core–shell–corona one with pH value.Display Omitted► pH-sensitive mixed micelles were readily formed by comicellization of two copolymers. ► The mixed micelles could be kept stable in wide pH range. ► The mixed micelles exhibited low cytotoxicity and high positive zeta potential. ► An increase in pH accelerated the release of drug from mixed micelles in vitro.Comicellization of a star block copolymer poly( ε-caprolactone)- block-poly(diethylamino)ethyl methacrylate (S(PCL- b-PDEAEMA)) and a linear block copolymer methoxy poly(ethylene glycol)- block-poly( ε-caprolactone) (mPEG- b-PCL) was developed to enhance the stability and lower the cytotoxicity of the micelles. The two copolymers self-assembled into the mixed micelles with a common PCL core surrounded by a mixed PDEAEMA/mPEG shell in aqueous solution. This core–shell structure was transformed to the core–shell–corona structure at high pH due to the collapse of the PDEAEMA segment. The properties of the polymeric micelles were greatly dependent on the weight ratio of the two copolymers and the external pH. As increasing the mPEG- b-PCL content, the size and the zeta potential of the mixed micelles were lowered while the pH-dependent stability and the biocompatibility were improved. Moreover, an increase in pH accelerated the release of indomethacin (IND) from the mixed micelles in vitro. These results augured that the mixed micelles could be applied as a stable pH-sensitive release system.
Keywords: Mixed micelles; pH-Sensitivity; Star copolymer; Self-assembly; Drug release
Synthesis and characterization of dendritic and porous Ag–Pd alloy nanostructures
by Limiao Chen; Younian Liu (pp. 100-106).
Ag-Pd alloy nanostructures with different morphologies were prepared and used as SERS substrates.Display Omitted► Dendritic and porous Ag–Pd alloy nanostructures were fabricated on the surface of silicon substrate by simple methods. ► Ag–Pd alloy nanostructures together with the silicon substrate can be directly used as SERS substrate to probe molecules. ► The dendritic and porous Ag–Pd nanostructures exhibit high SERS activity.Dendritic and porous Ag–Pd alloy nanostructures were successfully fabricated on the surface of silicon substrate using the co-reduction method and galvanic replacement reaction, respectively. The molar compositions of Ag and Pd in the alloy could be modulated by controlling the molar ratios of metal precursors and reaction time. The Ag–Pd alloy nanostructures were characterized by transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX), and X-ray diffraction (XRD). The morphology and phase of Au–Pd alloy nanostructures were discussed as a function of molar ratios of metal precursors and reaction time. In addition, the morphology and composition-dependent surface-enhanced Raman scattering (SERS) of the as-synthesized Ag–Pd alloy nanostructures were investigated. The SERS enhancement factor was estimated and SERS mapping was performed to prove the homogeneity of these substrates. The results indicate that as-synthesized dendritic and porous Ag–Pd alloy nanostructures are good candidates for SERS spectroscopy.
Keywords: Alloy; Synthesis; Morphology; Surface enhanced Raman scattering
Effect of polymer molecular weight on the fiber morphology of electrospun mats
by Hem Raj Pant; Ki-Taek Nam; Hyun-Ju Oh; Gopal Panthi; Hee-Dong Kim; Byung-il Kim; Hak Yong Kim (pp. 107-111).
By adding the solvent degraded nylon-6 solution in freshly prepared nylon-6 solution, the spider-net like fibrous mat was successfully prepared by electrospinning.Display Omitted► Large amounts of sub-nanofibers were obtained from solvent degraded solution. ► Nano and sub-nanofibers were arranged in spider-net like structure. ► Increased solvent degraded fraction can increase the number of thinner fibers. ► BET area, mechanical strength, and hydrophilicity were found to be increased.In this work, different fractions of solvent-induced polymer degraded solution were mixed with freshly prepared solution of same polymer, and its effect on fiber morphology of electrospun mats was investigated. Nylon-6 solution in formic acid was allowed to degrade for 3weeks and different fractions of it were mixed with freshly prepared nylon-6 solution to get the electrospun mats. FE–SEM images of the mats indicated that the a large amount of sub-nanofibers (<50nm in diameter) in the form of spider-net like structures were achieved by tailoring the amount of solvent degraded polymer solution in the freshly prepared nylon-6 solution. Large quantity of these ultrafine sub-nanofibers present in electrospun nylon-6 mats could increase its hydrophilicity and mechanical strength. The decreased average pore diameter and increased BET surface area of the mat, caused by spider-net like structure, can make it as a potential candidate for air/water filtration.
Keywords: Electrospinning; Degradation; Nylon-6; Sub-nanofibers; Spider-net
Hollow capsules prepared from all block copolymer micelle multilayers
by Jinkee Hong; Jinhan Cho; Kookheon Char (pp. 112-117).
Hollow capsules prepared from block copolymer micelle multilayers coated polystyrene colloidal particlesDisplay Omitted► We introduce all micelle based hollow multilayer capsules. ► Block copolymer micelles were used as building blocks for films. ► Layer-by-layer assembled multilayer films are coated onto colloids. ► Hollow capsules are containing functional hydrophobic components. ► Stabilities of capsules are depends on charge density and molecular weight ratio.We introduce a novel and versatile approach for preparing hollow multilayer capsules containing functional hydrophobic components. Protonated polystyrene- block-poly(4-vinylpyridine) (PS- b-P4VP) and anionic polystyrene- block-poly(acrylic acid) (PS- b-PAA) block copolymer micelles (BCM) were used as building blocks for the layer-by-layer assembly of BCM multilayer films onto polystyrene (PS) colloids. After removing the PS colloids, the stabilities of the formed BCM hollow capsules were found to be strongly dependent on the charge density of the hydrophilic corona segments (i.e., P4VP and PAA block segments) as well as the relative molecular weight ratio of hydrophobic core (i.e., PS segments) blocks and hydrophilic corona shells. Furthermore, in the case of incorporating hydrophobic fluorescent dyes into the PS core blocks of micelles, the hairy/hairy BCM multilayers showed well-defined fluorescent images after colloidal template removal process. These phenomena are mainly caused by the relatively high degree of electrostatic interdigitation between the protonated and anionic corona block shells.
Keywords: Hollow capsule; Micelle; Block copolymer; Layer-by-layer; Multilayer
Hydration kinetics of tricalcium silicate by calorimetric methods
by Francesca Ridi; Emiliano Fratini; Paola Luciani; Frank Winnefeld; Piero Baglioni (pp. 118-124).
DSC is a reliable analytical technique to study the cement hydration by monitoring the unreacted water. This opens new possibilities for the investigation of more complex cement samples containing superplasticizers.Display Omitted► The hydration reaction of a tricalcium silicate paste is studied using DSC. ► DSC method and the classical IC method are well in accordance. ► Boundary Nucleation and Growth Model is applied to compare DSC and IC techniques.The kinetics of the cement hydration reaction is a relevant issue in the cement research field, particularly in the presence of additional inorganic and organic components that consistently increase the complexity of the cement paste. In the present study, the hydration reaction of pure tricalcium silicate has been monitored by different calorimetric approaches: the conventional Isothermal Conduction Calorimetry (IC) and a novel Differential Scanning Calorimetry (DSC) protocol. The measured hydration curves have been modeled by using the Boundary Nucleation and Growth Model (BNGM) to extract thermodynamic parameters of the early stages of the hydration reaction. IC and DSC methods provide similar results in terms of rate constants, linear growth, and nucleation rates even though the IC accesses the total evolved heat while DSC discloses the fraction of unreacted water. The validation of the DSC approach as a reliable analytical method to the study of cement hydration kinetic is of particular importance because it allows following very long hydration processes, such as those of pastes containing organic retarders or superplasticizers. The thermodynamic and kinetic parameters for the tricalcium silicate setting has been also evaluated and discussed as a function of the surface area of the powder.
Keywords: Tricalcium silicate; Hydration kinetics; Differential Scanning Calorimetry; Isothermal Conduction Calorimetry; Boundary Nucleation and Growth Model; Cement; Free Water Index
Optical properties of Yeast Cytochrome c monolayer on gold: An in situ spectroscopic ellipsometry investigation
by Chiara Toccafondi; Mirko Prato; Giulia Maidecchi; Amanda Penco; Francesco Bisio; Ornella Cavalleri; Maurizio Canepa (pp. 125-132).
Spectroscopic ellipsometry allows to control the state of Yeast Cytochrome c molecules adsorbed on gold (left) through the detection of absorptions related to the heme group (right).Display Omitted► In situ spectroscopic ellipsometry of Cytochrome c monolayer on ultraflat gold. ► Sharp spectral features related to Soret band typical of heme group are identified. ► A simple isotropic optical model reproduces ellipsometric spectra quantitatively. ► Accurate estimate of film thickness and of optical properties of molecules. ► Adsorbed molecules under wet conditions preserved their native structureThe adsorption of Yeast Cytochrome c (YCC) on well defined, flat gold substrates has been studied by Spectroscopic Ellipsometry (SE) in the 245–1000nm wavelength range. The investigation has been performed in aqueous ambient at room temperature, focusing on monolayer-thick films. In situ δΨ and δΔ difference spectra have shown reproducibly well-defined features related to molecular optical absorptions typical of the so-called heme group. The data have been reproduced quantitatively by a simple isotropic optical model, accounting for the molecular absorption spectrum and film-substrate interface effects. The simulations allowed a reliable estimate of the film thickness and the determination of the position and the shape of the so-called Soret absorption peak that, within the experimental uncertainty, is the same found for molecules in liquid. These findings suggest that YCC preserves its native structure upon adsorption. The same optical model was able to reproduce also ex situ results on rinsed and dried samples, dominated by the spectral features associated to the polypeptide chain that tend to overwhelm the heme absorption features.
Keywords: Yeast Cytochrome; c; Gold; Optical properties; Spectroscopic ellipsometry
Properties of β-sitostanol/DPPC monolayers studied with Grazing Incidence X-ray Diffraction (GIXD) and Brewster Angle Microscopy
by Katarzyna Hąc-Wydro; Michał Flasiński; Marcin Broniatowski; Patrycja Dynarowicz-Łątka; Jarosław Majewski (pp. 133-139).
π-A isotherm for β-sitostanol/DPPC monolayer ( Xβ-sitostanol=0.3) and BAM images taken at various stages of compression. Bragg peak I(Q xy) profile (A) and corresponding Bragg rod profile I(Q y) (B) for β-sitostanol/DPPC film ( Xβ-sitostanol=0.3) ( π=30mN/m).Display Omitted► In-plane organization of β-sitostanol/DPPC films studied with GIXD technique. ► Molecular arrangement of phytostanol/DPPC mixtures depends on films composition. ► Extend of the in-plane order of films decreases with the addition of stanol. ► The ordered domains in the mixed systems consist of both monolayer’s components.Although the influence of structurally modified sterols on artificial membranes has been intensively investigated, studies on the properties of stanols, which are saturated analogs of sterols, are very rare. Therefore, we have performed Grazing Incidence X-ray Diffraction (GIXD) experiments aimed at studying in-plane organization of a plant stanol–β-sitostanol monolayer and its mixtures with 1,2-dipalmitoyl- sn-glycero-3-phosphocholine – DPPC at the air/water interface. The collected GIXD data, resulting in-plane parameters and BAM images provide information on molecular organization and in-plane ordering of the investigated films. It was found that the lateral organization of β-sitostanol/DPPC monolayers depends on their composition. The oblique structure of the in-plane lattice of tilted hydrophobic region of molecules, found for DPPC film, is maintained at 10mol% of stanol in the system. However, at 30 and 90mol% of stanol in the mixture, the arrangement of molecules is hexagonal and they are oriented perpendicularly to the interface. With the addition of stanol the extend of the in-plane order of the monolayers decreases. Moreover, in mixtures the ordered domains consist of both monolayer’s components. Additionally, β-sitostanol film is of similar in-plane organization as the corresponding sterol monolayer (β-sitosterol) and stanol induces condensing effect on DPPC.
Keywords: Langmuir monolayer; Plant sterols; Grazing Incidence X-ray Diffraction (GIXD); Brewster Angle Microscopy
Phase-assisted synthesis and DNA unpacking evaluation of biologically inspired metallo nanocomplexes using peptide as unique building block
by N. Raman; S. Sudharsan (pp. 140-147).
Novel metallo nanocomplexes have been synthesized via modified Brust–Schiffrin methodology using peptide as their building block. Biological inspiration of all the nanocomplexes is driven by their embedding peptide PrHA.Display Omitted► Novel metallo nanocomplexes synthesized via modified Brust–Schiffrin approach. ► Among all the products, zinc and cobalt nanocomplexes unpack the DNA most efficiently. ► Biological inspirations of nanocomplexes are proved by targeting bacterial and fungal strains. ► Biological inspiration of the metallo nanocomplexes is driven by their size and the peptide PrHA.The goal of nanomaterials’ surface modification using a biomaterial is to preserve the materials’ bulk properties while modifying only their surface to possess desired recognition and specificity. Here, we have developed a phase-assisted, modified Brust–Schiffrin methodological synthesis of metallo nanocomplexes anchored by a peptide, N,N′-(1,3-propylene)- bis-hippuricamide. The spectral, thermal and morphological characterizations assure the formation of nanocomplexes. Therapeutic behavior of all the nanocomplexes has been well sighted by evaluating their DNA unpacking skills. In addition, we demonstrate their biological inspiration by targeting few bacterial and fungal strains. The in vitro antimicrobial investigation reports that all the nanocomplexes disrupt microbial cell walls/membranes efficiently and inhibit the growth of microbes. These sorts of nanocomplexes synthesized in large quantities and at low cost, deliver versatile biomedical applications, and can be used to treat various diseases which may often cause high mortality.
Keywords: Nanocomplex; Peptide; Brust–Schiffrin; DNA unpacking; Biological inspiration
Solubilisation of different medium chain esters in zwitterionic surfactant solutions – Effects on phase behaviour and structure
by A. Barth; S. Prévost; J. Popig; M. Dzionara; G. Hedicke; M. Gradzielski (pp. 148-156).
Phase and SANS study of surfactant/ester/water systems with differently long esters. Systematic correlations exist between structural and phase behaviour of the systems and the bending rigidity of their amphiphilic film.Display Omitted► Phase in ternary surfactant systems shift systematically with length of ester. ► Quantitative analysis of the rod-to-lamellae-to-sphere transition. ► Bending constant2κ+κ¯ increases with chain length of the ester. ► Stability of the lamellar phase directly related to2κ+κ¯.We studied the effect of solubilisation of methyl esters with different chains of medium length into the binary surfactant system tetradecyldimethylamine oxide/water at constant surfactant concentration of 200mM. As esters we employed valeric, capronic, enanthic, and pelargonic methyl ester, thereby decreasing the polarity. Always a phase sequence L1–Lα–L1 is observed with increasing ester concentration, where the Lα-phase increases in extent and goes to much lower temperatures with increasing chain length of the ester. Viscosity measurements show a maximum at intermediate concentrations of additive that is independent of the type of ester. From SANS measurements detailed information about the structural changes occurring during the rod-to-sphere transition in the system of the shortest additive is deduced, which proceeds first through a pronounced rod growth. Interestingly, for the different esters an almost constant value of the volumic solubilisation capacity is observed, in agreement with the relatively constant interfacial tension. For the different esters no effect on the radius and the area requirement at the amphiphilic interface is observed at the solubilisation boundary. The microemulsions present here are spherical aggregates where the ester is partitioned between core and shell. From the SANS and interfacial tension data the effective bending constants of the surfactant monolayers were deduced and they show that the extension of the Lα-phase is directly related to a corresponding increase in the bending constants of the surfactant/ester monolayers.
Keywords: Zwitterionic surfactant; Ester; Cosurfactant; Phase diagram; SANS
Refolding of bovine serum albumin via artificial chaperone protocol using gemini surfactants
by Nuzhat Gull; Mohammad Amin Mir; Javed Masood Khan; Rizwan Hassan Khan; Ghulam Mohammad Rather; Aijaz Ahmad Dar (pp. 157-162).
The present finding shows the excellent efficacy of gemini surfactants as capturing agents during artificial chaperone protocol for achieving refolding of BSA.Display Omitted► We report refolding of BSA through artificial chaperone protocol using gemini surfactants. ► The studies were performed using circular dichroism, DLS and fluorescence studies. ► Results show geminis’ to be more useful in the protein refolding than conventional surfactants.Surfactants prevent the irreversible aggregation of partially refolded proteins, and they are also known to assist in protein refolding. A novel approach to protein refolding that utilizes a pair of low molecular weight folding assistants, a detergent and cyclodextrin, was proposed by Rozema and Gellman (D. Rozema, S.H. Gellman, J. Am. Chem. Soc. 117 (1995) 2373). We report the refolding of bovine serum albumin (BSA) assisted by these artificial chaperones, utilizing gemini surfactants for the first time. A combination of cationic gemini surfactants, bis(cetyldimethylammonium)pentane dibromide (C16H33(CH3)2N+–(CH2)5–N+(CH3)2C16H33·2Br− designated as G5 and bis(cetyldimethylammonium)hexane dibromide (C16H33(CH3)2N+–(CH2)6–N+(CH3)2C16H33·2Br− designated as G6 and cyclodextrins, was used to refold guanidinium chloride (GdCl) denatured BSA in the artificial chaperone assisted two step method. The single chain cationic surfactant cetyltrimethylammonium bromide (CTAB) was used for comparative studies. The studies were carried out in an aqueous medium at pH 7.0 using circular dichroism, dynamic light scattering and ANS binding studies. The denatured BSA was found to get refolded by very small concentrations of gemini surfactant at which the single chain counterpart was found to be ineffective. Different from the single chain surfactant, the gemini surfactants exhibit much stronger electrostatic and hydrophobic interactions with the protein and are thus effective at much lower concentrations. Based on the present study it is expected that gemini surfactants may prove useful in the protein refolding operations and may thus be effectively employed to circumvent the problem of misfolding and aggregation.
Keywords: Gemini surfactant; Artificial chaperone; Bovine serum albumin; Circular dichroism; Dynamic light scattering; Intrinsic fluorescence; Extrinsic fluorescenceAbbreviations; BSA; bovine serum albumin; CTAB; cetyltrimethylammonium bromide; G5; bis(cetyldimethylammonium)pentane dibromide; G6; bis(cetyldimethylammonium)hexane dibromide; ANS; 1-anilino-8-naphthalenesulphonate; CD; circular dichroism; DLS; dynamic light scattering
Solubilization of triphenylamine, triphenylphosphine, triphenylphosphineoxide and triphenylmethanol in single and binary surfactant systems
by Mohammad Amin Mir; Oyais Ahmad Chat; Muzaffar Hussain Najar; Mohammad Younis; Aijaz Ahmad Dar; Ghulam Mohammad Rather (pp. 163-169).
Correlation of λmax (nm) of Triphenyl phosphine oxide (TPPO) in various surfactants and the model solvents at 25°C to provide an insight into its locus of solubilization in these surfactant assemblies.Display Omitted► We report solubilization of triphenyls in single and mixed surfactant systems. ► The solubilization capacity of the micelles was dependent on the locus of solubilization and structure of the solubilizates. ► The extent of co-solubilization is strongly affected by the competition for the same solubilization site. ► The locus of solubilization of triphenylphosphine within micelles significantly affects its rate of oxidation.Solubilization and co-solubilization of triphenyls (TPs) viz., triphenylphosphine (TPP), triphenylphosphineoxide (TPPO), triphenylamine (TPA) and triphenylmethanol (TPM) were studied in various single and binary surfactant systems at 25°C using UV–visible spectroscopy and HPLC. The solubilization capacities of different micelles towards TPs were found to be a function of the nature and structure of solubilizates, locus of solubilization, size of micelles and the nature of interactions between the solubilizate and micelles. The effect of surfactant mixing on the solubilization of TPs was evaluated using the Regular Solution Approach (RSA). The solubility enhancement of TPs within mixed micelles relative to that observed in single surfactant systems was explained in light of the structural micellar changes associated with the mixing of ionic and non-ionic surfactants. Moreover, kinetics of oxidation of TPP by hydrogen peroxide investigated in these surfactant systems was found to be sensitive to the nature of micelle and the locus of solubilization of TPP within the micelles.
Keywords: Surfactants; Synergism; Triphenyls; Solubilization; Co-solubilization; Micelles
Thermodynamic studies on thin liquid films IV. Foam film stabilized by sodium dodecyl sulfate
by Hidemi Iyota; Norihiro Ikeda; Rumen Krastev (pp. 170-177).
Phase transition between the black films is accompanied by the discontinuous changes in the core-thickness and in the surface densities of NaCl and SDS at the film surfaces.Display Omitted► Film thickness and surface densities change discontinuously at the transition between black films. ► The transition occurs only above 0.193molkg−1 NaCl. ► Miscibility of NaCl and SDS increases in the order, water/air interface
Keywords: Black foam film; Sodium dodecyl sulfate; Contact angle; Film thickness; Phase transition; Thermodynamics; Phase diagram; Miscibility; Adsorbed film
The effect of heating temperature and nitric acid treatments on the performance of Cu- and Zn-based broad spectrum respirator carbons
by J.W.H. Smith; J.V. Romero; T.R. Dahn; K. Dunphy; B. Sullivan; M. Mallay; L.M. Croll; J.H. Reynolds; C. Andress; J.R. Dahn (pp. 178-194).
SEM images of the inner pores of impregnated activated carbon samples prepared using the same precursor. The left and right images were obtained from samples heated at 180°C and 450°C respectively.Display Omitted► Nitric acid treatments decreased metal oxide grain size. ► Well dispersed, small grain size impregnants had good gas adsorption capacity. ► Appropriate thermal treatments were key to impregnant phase and performance. ► Zn-based samples with simple chemistry and synthesis were found to perform well.Impregnated activated carbons (IACs) that are used in broad spectrum gas mask applications have historically contained copper and/or zinc impregnants. The addition of an oxidizing agent, such as nitric acid (HNO3) can be useful in distributing the metallic impregnants uniformly on the activated carbon substrate. In this work, we study IACs prepared from copper nitrate (Cu(NO3)2) and zinc nitrate (Zn(NO3)2) precursors as a function of HNO3 content present in the impregnating solution and as a function of heating temperature. The gas adsorption capacity of the IACs was determined by dynamic flow testing using sulfur dioxide (SO2), ammonia (NH3), hydrogen cyanide (HCN) and cyclohexane (C6H12) challenge gases under dry and humid conditions. The thermal decomposition and distribution of the impregnant on the activated carbon substrate is studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis techniques. Relationships between gas adsorption capacity, impregnant distribution and the species of surface impregnants are discussed.
Keywords: Impregnated activated carbon; Impregnant grain size; Nitric acid treatment; Thermal decomposition; Gas adsorption capacity
Adsorption rate of phenol from aqueous solution onto organobentonite: Surface diffusion and kinetic models
by Raul Ocampo-Perez; Roberto Leyva-Ramos; Jovita Mendoza-Barron; Rosa M. Guerrero-Coronado (pp. 195-204).
Display Omitted► Phenol adsorption capacity of organobentonite decreased with temperature. ► Overall adsorption rate of phenol onto organobentonite was modeled in this work. ► External mass transport did not affect the adsorption rate of phenol. ► Adsorption rate of phenol on organobentonite was controlled by surface diffusion. ► Second-order and Langmuir kinetic models fitted the rate data reasonably well.The concentration decay curves for the adsorption of phenol on organobentonite were obtained in an agitated tank batch adsorber. The experimental adsorption rate data were interpreted with diffusional models as well as first-order, second-order and Langmuir kinetic models. The surface diffusion model adjusted the data quite well, revealing that the overall rate of adsorption was controlled by surface diffusion. Furthermore, the surface diffusion coefficient increased raising the mass of phenol adsorbed at equilibrium and was independent of the particle diameter in the range 0.042–0.0126cm. It was demonstrated that the overall rate of adsorption was essentially not affected by the external mass transfer. The second-order and the Langmuir kinetic models fitted the experimental data quite well; however, the kinetic constants of both models varied without any physical meaning while increasing the particle size and the mass of phenol adsorbed at equilibrium.
Keywords: Adsorption; Diffusion; Kinetics; Mass transfer; Organobentonite; Phenol
Adsorption kinetics, capacity and mechanism of arsenate and phosphate on a bifunctional TiO2–Fe2O3 bi-composite
by Mitch D’Arcy; Dominik Weiss; Michael Bluck; Ramon Vilar (pp. 205-212).
Illustration of the proposed adsorption binding mechanism of AsV onto the TiO2–Fe2O3 bi-composite, based on kinetic and adsorption isotherm modelling.Display Omitted► Fast and simple method for the synthesis of TiO2–Fe2O3 bi-composites. ► As and P adsorbed within one minute and strongly bound over days. ► Modified rate equation models kinetics as two simultaneous reactions. ► Adsorption interpreted as parallel mono- and bi-dentate complexation. ► Adsorption capacity is 12mgAsg−1 in slightly acidic conditions.Mixed oxide TiO2–Fe2O3 bi-composites have been recognised as efficient and economical sorbents with great promise for arsenic removal from groundwater. In this study, we use a fast, simple and inexpensive synthesis method for this type of bi-composite and assess its adsorption performance. The kinetics of arsenate and phosphate adsorption onto the bi-composite are determined, demonstrating rapid and stable uptake of both oxy-anions over several days and with improved performance compared to the widely used TiO2 sorbent. A modified pseudo-second order rate equation is introduced, which allows the adsorption kinetics to be modelled as two simultaneous, parallel reaction pathways with separate kinetic parameters. This equation reproduces the experimental observations accurately across a wide range of timescales from minutes to days. Our experimental data agrees with previous interpretations of the adsorption mechanism including the formation of mono-dentate and bi-dentate inner-sphere surface complexes. The arsenate and phosphate uptake capacities of the bi-composite are reported. Equilibrium studies were conducted between pH 5 and 9 and interpreted within the Langmuir, Freundlich and Dubinin–Radushkevich isotherm models.
Keywords: Adsorption; Arsenate; Phosphate; Iron titanium oxide; Langmuir; Freundlich; Dubinin–Radushkevich; Adsorption kinetics; Pseudo-second order rate law
Bacteria attachment to surfaces – AFM force spectroscopy and physicochemical analyses
by Ardiyan Harimawan; Aruliah Rajasekar; Yen-Peng Ting (pp. 213-218).
Bacterial cell was successfully coated to AFM tip (a) to measure the adhesion force between bacteria and stainless steel surfaces (b) with various surface delays.Display Omitted► AFM force measurement using live bacteria. ► Nature of adhesion mechanism of bacteria on stainless steel were explored. ► Higher adhesion force on Gram-negative bacteria. ► Physicochemical analysis support force measurements. ► EPS production enhanced bacterial adhesion.Understanding bacterial adhesion to surfaces requires knowledge of the forces that govern bacterial–surface interactions. Biofilm formation on stainless steel 316 (SS316) by three bacterial species was investigated by examining surface force interaction between the cells and metal surface using atomic force microscopy (AFM). Bacterial–metal adhesion force was quantified at different surface delay time from 0 to 60s using AFM tip coated with three different bacterial species: Gram-negative Massilia timonae and Pseudomonas aeruginosa, and Gram-positive Bacillus subtilis. The results revealed that bacterial adhesion forces on SS316 surface by Gram-negative bacteria is higher (8.53±1.40nN and 7.88±0.94nN) when compared to Gram-positive bacteria (1.44±0.21nN). Physicochemical analysis on bacterial surface properties also revealed that M. timonae and P. aeruginosa showed higher hydrophobicity and surface charges than B. subtilis along with the capability of producing extracellular polymeric substances (EPS). The higher hydrophobicity, surface charges, and greater propensity to form EPS by M. timonae and P. aeruginosa led to high adhesive force on the metal surface.
Keywords: Biofilm; Hydrophobicity; Adhesion force; P. aeruginosa; B. subtilis; M. timonae
Superhydrophobic silicon surfaces with micro–nano hierarchical structures via deep reactive ion etching and galvanic etching
by Yang He; Chengyu Jiang; Hengxu Yin; Jun Chen; Weizheng Yuan (pp. 219-229).
Superhydrophobic silicon surfaces with micro–nano hierarchical structures were fabricated by deep reactive ion etching and galvanic etching. Wettability analysis using two-scale model composed of micropillar and nanopillar arrays indicated that superhydrophobic surface may demonstrate a hybrid wetting state.Display Omitted► A novel fabrication method for silicon hierarchical structures is presented. ► The forming mechanism and the effects of process parameters were discussed. ► CA measurement and tilting/dropping test show the surfaces were superhydrophobic. ► Two-scale model composed of micropillar and nanopillar arrays was proposed. ► Superhydrophobic surface may demonstrate a hybrid wetting state.An effective fabrication method combining deep reactive ion etching and galvanic etching for silicon micro–nano hierarchical structures is presented in this paper. The method can partially control the morphology of the nanostructures and enables us to investigate the effects of geometry changes on the properties of the surfaces. The forming mechanism of silicon nanostructures based on silver nanoparticle galvanic etching was illustrated and the effects of process parameters on the surface morphology were thoroughly discussed. It is found that process parameters have more impact on the height of silicon nanostructure than its diameter. Contact angle measurement and tilting/dropping test results show that as-prepared silicon surfaces with hierarchical structures were superhydrophobic. What’s more, two-scale model composed of micropillar arrays and nanopillar arrays was proposed to study the wettability of the surface with hierarchical structures. Wettability analysis results indicate that the superhydrophobic surface may demonstrate a hybrid state at which water sits on nanoscale pillars and immerses into microscale grooves partially.
Keywords: Superhydrophobic; Hierarchical structure; Deep reactive ion etching; Galvanic etching; Two-scale model
Drop shape visualization and contact angle measurement on curved surfaces
by Manfredo Guilizzoni (pp. 230-236).
Static, as-placed contact angles are estimated from side views of sessile drops on curved surfaces without need of any preliminary information.Display Omitted► Drop shape on curved surfaces is visualized. ► Contact angle is determined on flat and curved surfaces with no a priori information. ► Contact angle measurement on three-dimensional sculptured surfaces is performed. ► Gemstones wettability is analyzed.The shape and contact angles of drops on curved surfaces is experimentally investigated. Image processing, spline fitting and numerical integration are used to extract the drop contour in a number of cross-sections. The three-dimensional surfaces which describe the surface–air and drop–air interfaces can be visualized and a simple procedure to determine the equilibrium contact angle starting from measurements on curved surfaces is proposed. Contact angles on flat surfaces serve as a reference term and a procedure to measure them is proposed. Such procedure is not as accurate as the axisymmetric drop shape analysis algorithms, but it has the advantage of requiring only a side view of the drop–surface couple and no further information. It can therefore be used also for fluids with unknown surface tension and there is no need to measure the drop volume. Examples of application of the proposed techniques for distilled water drops on gemstones confirm that they can be useful for drop shape analysis and contact angle measurement on three-dimensional sculptured surfaces.
Keywords: Drop shape visualization; Contact angle measurement; Curved surfaces; Gemstones
Wettability determination by contact angle measurements: hvbB coal–water system with injection of synthetic flue gas and CO2
by Narjes Shojai Kaveh; E. Susanne J. Rudolph; Karl-Heinz A.A. Wolf; Seyed Nezameddin Ashrafizadeh (pp. 237-247).
Stable and non-stable contact angles of a synthetic flue gas and pure CO2 on an hvbB coal were determined in a pressure range between atmospheric to 16MPa using a modified pendant drop cell at a constant temperature of 318K.Display Omitted► The wetting behavior was evaluated on a hvbB coal surface by synthetic flue gas and CO2 injection. ► Contact angle increases with pressure and surface becomes gas wet for CO2 injection. ► Wettability alters to intermediate wet for synthetic flue gas injection as pressure increases. ► Synthetic flue gas experiments show that mainly CO2 sorbs and not nitrogen. ► Experimental results are comparable to CO2 results at the same CO2 (partial) pressures.Geological sequestration of pure carbon dioxide (CO2) in coal is one of the methods to sequester CO2. In addition, injection of CO2 or flue gas into coal enhances coal bed methane production (ECBM). The success of this combined process depends strongly on the wetting behavior of the coal, which is function of coal rank, ash content, heterogeneity of the coal surface, pressure, temperature and composition of the gas. The wetting behavior can be evaluated from the contact angle of a gas bubble, CO2 or flue gas, on a coal surface. In this study, contact angles of a synthetic flue gas, i.e. a 80/20 (mol%) N2/CO2 mixture, and pure CO2 on a Warndt Luisenthal (WL) coal have been determined using a modified pendant drop cell in a pressure range from atmospheric to 16MPa and a constant temperature of 318K.It was found that the contact angles of flue gas on WL coal were generally smaller than those of CO2. The contact angle of CO2 changes from water-wet to gas-wet by increasing pressure above 8.5MPa while the one for the flue gas changes from water-wet to intermediate-wet by increasing pressure above 10MPa.
Keywords: Contact angle; Wettability; CO; 2; Sequestration; Wet hvbB coal; Flue gas
A floating prolate spheroid
by C. Pozrikidis (pp. 248-256).
Illustration of a contact line developing around a floating spheroidal particle with aspect ratio c/ b=5, drawn as a heavy line. The rectangular frame marks the position of the undisturbed interface.Display Omitted► Developed an efficient method for estimating the equilibrium position of a floating elongated particle. ► Demonstrated the effect of physical and geometrical parameters on the particle floating angle. ► Reconstructed the shape of the three-phase contact line.The equilibrium position of a spherical or prolate spheroidal particle resembling a needle floating at the interface between two immiscible fluids is discussed. A three-dimensional meniscus attached to an a priori unknown contact line at a specified contact angle is established around the particle, imparting to the particle a capillary force due to surface tension that is balanced by the buoyancy force and the particle weight. An accurate numerical solution for a floating sphere is obtained by solving a boundary-value problem, and the results are compared favorably with an approximate solution where the effect of the particle surface curvature is ignored and the elevation of the contact line is computed using an analytical solution for the meniscus attached to an inclined flat plate. The approximate formulation is applied locally around the nearly planar elliptical contact line of a prolate spheroid to derive a nonlinear algebraic equation governing the position of the particle center and the mean elevation of the contact line. The effect of the fluid and particle densities, contact angle, and capillary length is discussed, and the shape of the contact line is reconstructed and displayed from the local solution.
Keywords: Hydrostatics; Floating spheroid
Excess thermodynamic properties of thin water films confined between hydrophobized gold surfaces
by Jialin Wang; Roe-Hoan Yoon; Jan Christer Eriksson (pp. 257-263).
For the hydrophobic interaction between C16SH-coated gold surfaces at 20°C, both the enthalpy (Δ Hf) and entropy ( TΔ Sf) changes are negative. Under these conditions, the free energy change (Δ Gf) becomes negative (or attractive force appears) only when |Δ Hf|>| TΔ Sf|.Display Omitted► Hydrophobic forces were measured systematically at different temperatures. ► Macroscopic hydrophobic interaction entails decreases in both entropy and enthalpy. ► Macroscopic hydrophobic interaction is enthalpically driven.Surface forces between gold surfaces were measured in pure water at temperatures in the range of 10–40°C using an atomic force microscope (AFM). The surfaces were hydrophobized by self-assembly of alkanethiols (C nSH) with n=2 and 16 in ethanol solutions. The data were used to determine the changes in excess free energies (Δ Gf) of the thin water films per unit area by using the Derjaguin approximation . The free energy data were then used to determine the changes in excess film entropy (Δ Sf) and the excess film enthalpy (Δ Hf) per unit area. The results show that both Δ Sf and Δ Hf decrease with decreasing film thickness, suggesting that the macroscopic hydrophobic interaction involves building some kind of structures in the intervening thin films of water. It was found that |Δ Hf|>| TΔ Sf|, which is a necessary condition for an attractive force to appear when the enthalpy and entropy changes are both negative. That macroscopic hydrophobic interaction is enthalpically driven is contrary to the hydrophobic interactions at molecular scale. The results obtained in the present work are used to discuss possible origins for the long-range attractions observed between hydrophobic surfaces.
Keywords: Enthalpy–entropy compensation; Alkanethiol; Surface force; Hydrophobic force; DLVO theory; Temperature effect; Thin films of water; Low-density liquid (LDL); Clathrate
Investigation of pH-responsive properties of polymeric micelles with a core-forming block having pendant cyclic ketal groups
by Shan Jiang; Yuan Yao; Yanzhao Nie; Junjiao Yang; Jing Yang (pp. 264-271).
The release behavior of polymeric micelles from MPEG- block-PDMMA triggered at pH 3.5 and 37°C depended on the chemical architecture with miceller size expansion.Display Omitted► The pH-responsiveness was tunable depending on chemical structure of the polymers. ► The transformation from an amphiphilic polymer to a doubly hydrophilic polymer was detected. ► Changes in both pH and temperature generated the encapsulated molecule release from the polymeric micelles.In this study, three kinds of amphiphilic block copolymers, termed MPEG- block-PDMMA, MPEG- block-PCPMA, and MPEG- block-PMPMA, which were composed of one hydrophilic monomethoxy poly(ethylene glycol) (MPEG) block and one hydrophobic polyacrylate block bearing pendant six-member cyclic ketal groups, were synthesized by atom transfer radical polymerization (ATRP). These polymers can disperse in aqueous media to self-assemble into micellar aggregates with a spherical core-shell structure with mean diameter below 300nm. The stimuli-responsiveness of polymeric micelles from MPEG- block-PDMMA was detected by fluorescence-probe technique at pH 3.5 and 37°C. The effect of chemical architecture and composition of the polymers on the pH-responsive properties of polymeric micelles was also studied. A combination of pH and temperature to trigger release behavior of these polymeric micelles was discussed by comparing the encapsulated molecule release ability under various pH and temperature conditions and analyzing chemical structural changes of the polymer before and after the triggering.
Keywords: Polymeric micelles; pH-responsive; Nanomaterials; Biomaterials
Interaction of Au(III) and Pt(IV) complex ions with Fe(II) ions as a scavenging and a reducing agent: A basic study on the recovery of Au and Pt by a chemical method
by Pornthip Parinayok; Mamiko Yamashita; Kotaro Yonezu; Hironori Ohashi; Koichiro Watanabe; Yoshihiro Okaue; Takushi Yokoyama (pp. 272-275).
Au(III) complex ions are stoichiometrically and rapidly reduced to metallic gold prior to coprecipitation with Fe(OH)2, whereas Pt(IV) complex ions are reduced only after coprecipitation. It is a key to selective recovery of Au and Pt in the metallic state.Display Omitted► We separately recover Au and Pt in the metallic state by coprecipitation with Fe(II) hydroxide. ► Au(III) is stoichiometrically and rapidly reduced to metallic Au in acidic solution prior to coprecipitation. ► Pt(IV) is conversely reduced to Pt(II) and metallic Pt only after coprecipitation. ► Pt(II) can be also reduced to metallic Pt after coprecipitation.In order to develop a chemical technique for the recovery of gold (Au) and platinum (Pt) in the metallic state from spent catalysts, e.g., catalysts for environmental protection and automobile and petroleum catalysts, the coprecipitation behaviors of Au(III) and Pt(IV) complex ions with Fe(OH)2 as a scavenging and reducing agent were investigated. The Au(III) complex ions were found to be stoichiometrically and rapidly reduced to metallic Au due to electron transfer in acidic aqueous solution prior to coprecipitation with Fe(OH)2. Conversely, Pt(IV) complex ions were reduced only after coprecipitation with Fe(OH)2 due to electron transfer through a Pt(IV)–O–Fe(II) bond on the solid Fe(OH)2. Using this chemical technique, Au and Pt can be selectively and effectively recovered in the metallic state.
Keywords: Au(III) complex; Pt(IV) complex; Fe(II)ions; Reduction; Separation; Recovery
Considerations when determining low interfacial tensions
by Shima Afshar; Anthony Yeung (pp. 276-278).
Appearance of a bicontinuous liquid that was immiscible with the hydrocarbon and aqueous phases.Display Omitted► Possible pitfalls associated with low IFT measurements are highlighted. ► Surfactants may create inadvertent third phases that obscure IFT measurement. ► A new micropipette technique for quantifying ultralow IFTs is introduced. ► Micropipette can be combined with other techniques to yield new information.Surfactants are often used to create low or “ultralow” oil–water interfacial tensions (IFTs). These molecules, in some cases, may also lead to the inadvertent formation of microemulsion phases which can obscure IFT measurements. Here, we present a case study of such an issue. We also introduce a little-known micropipette technique which has many advantages over the more common spinning drop method for determining low/ultralow IFTs.
Keywords: Ultralow interfacial tensions; Bicontinuous microemulsions; Micropipette technique