Journal of Colloid And Interface Science (v.312, #2)
Molecular simulation of adsorption and separation of mixtures of short linear alkanes in pillared layered materials at ambient temperature
by Wen-Zhuo Li; Zi-Yang Liu; Yu-Liang Che; Dan Zhang (pp. 179-185).
Grand canonical Monte Carlo and configurational-bias Monte Carlo techniques are carried out to simulate the adsorption of ternary and quaternary mixtures of short linear alkanes, involving methane, ethane, propane, and n-butane, in pillared layered materials at ambient temperature,T=300K. In the simulation, a pillared layered pore is modeled by a uniform distribution of pillars between two layered walls built by making two separate talc lamellas parallel each other with a given size of interlayer distance. The interaction between fluid molecules and two layered walls is measured by storing potentials calculated in advance at a series of grid points. The interaction between fluid molecules and pillars is also calculated by a site-to-site method. The potential model proposed in this work is proved to be effective because of the simulation result being good agreement with the experimental data for the adsorption of nitrogen at 77 K. Then, the adsorption isotherms of mixtures of short linear alkanes in pillared layered pores with three different porositiesψ=0.98,0.93 and 0.85, and three pore widthsH=1.02,1.70 and 2.38 nm at 300 K are obtained by taking advantage of the model. The simulation results tell us that the longer chain component is preferentially adsorbed at low pressures, and its adsorption increases and then decreases as the pressure increases while the shorter chain component is still adsorbed at high pressures. Moreover, the sorption selectivity of pillared layered materials for the longest chain component in alkane mixtures increases as the mole fraction of methane in the gas phase increases. The selectivity of pillared layered materials for the longest chain component in alkane mixtures also increases as the pore width decreases and the porosity increases.The adsorption of ternary and quaternary mixtures of short linear alkanes, involving methane, ethane, propane, and n-butane, in pillared layered materials are investigated by molecular simulation techniques.
Keywords: Molecular simulation; Alkane mixtures; Adsorption and separation; Pillared layered materials
Adsorption characteristics of nanoporous carbon–silica composites synthesized from graphite oxide by a mechanochemical intercalation method
by Y.-H. Chu; M. Yamagishi; Z.-M. Wang; H. Kanoh; T. Hirotsu (pp. 186-192).
Nanoporous carbon–silica composites were synthesized from graphite oxide (GO) precursor by a mechanochemical intercalation (MCI) method at different conditions, and their structural property, thermal decomposition behaviors, and adsorption characteristics were examined. MCI method yields regular tetraethoxysilane (TEOS)-intercalated GO layer structures with controllable silicon content depending on the TEOS addition. Adsorption behaviors of water and hexane indicate the amphiphilic properties of the composites. The detailed porosities of the composites and their changes upon water adsorption were analyzed on the basis ofαs-plot method of N2 adsorption isotherms using a weight-averaged standard data from non-porous silica and non-porous carbon, which plausibly divides microporosity and mesoporosity.Nanoporous composite of carbon nanosheets and silica nanoparticles with surface amphiphilicity, and both micropores and mesopores.
Keywords: Nanoporous; Carbon–silica composite; Adsorption characterization
Fluorescence probe techniques to monitor protein adsorption-induced conformation changes on biodegradable polymers
by Johan Benesch; Graham Hungerford; Klaus Suhling; Carolyn Tregidgo; João F. Mano; Rui L. Reis (pp. 193-200).
The study of protein adsorption and any associated conformational changes on interaction with biomaterials is of great importance in the area of implants and tissue constructs. This study aimed to evaluate some fluorescent techniques to probe protein conformation on a selection of biodegradable polymers currently under investigation for biomedical applications. Because of the fluorescence emanating from the polymers, the use of monitoring intrinsic protein fluorescence was precluded. A highly solvatochromic fluorescent dye, Nile red, and a well-known protein label, fluorescein isothiocyanate, were employed to study the adsorption of serum albumin to polycaprolactone and to some extent also to two starch-containing polymer blends (SPCL and SEVA-C). A variety of fluorescence techniques, steady state, time resolved, and imaging were employed. Nile red was found to leach from the protein, while fluorescein isothiocyanate proved useful in elucidating a conformational change in the protein and the observation of protein aggregates adsorbed to the polymer surface. These effects were seen by making use of the phenomenon of energy migration between the fluorescent tags to monitor interprobe distance and the use of fluorescence lifetime imaging to ascertain the surface packing of the protein on polymer.We have used several fluorescence techniques to monitor changes in protein conformation upon adsorption. For example, label albumin with varying degree of FITC per albumin.
Keywords: Fluorescence; Anisotropy; Time resolved; Albumin; Protein conformation; Fluorescence lifetime imaging; Synchronous scan; Tryptophan; Nile red; Fluorescein isothiocyanate
Relaxation phenomena in poly(vinyl alcohol)/fumed silica affected by interfacial water
by V.M. Gun'ko; P. Pissis; A. Spanoudaki; V.I. Zarko; Y.M. Nychiporuk; L.S. Andriyko; E.V. Goncharuk; R. Leboda; J. Skubiszewska-Zięba; V.D. Osovskii; Y.G. Ptushinskii (pp. 201-213).
Interaction of poly(vinyl alcohol) (PVA) with fumed silica was investigated in the gas phase and aqueous media using adsorption, broadband dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization current (TSDC), infrared spectroscopy, thermal analysis, and one-pass temperature-programmed desorption (OPTPD) mass-spectrometry (MS) methods. PVA monolayer formation leads to certain textural changes in the system (after suspension and drying) because of strong hydrogen bonding of the polymer molecules to silica nanoparticles preventing strong interaction between silica particles themselves. This strong interaction promotes associative desorption of water molecules at lower temperatures than in the case of silica alone. Interaction of PVA with silica and residual water leads to depression of glass transition temperature (Tg). There are three types of dipolar relaxations at temperatures lower and higher than theTg value. A small amount of adsorbed water leads to significant conductivity with elevating temperature.Formation of a PVA monolayer on a silica surface leads to textural changes caused by strong interaction of the polymer with nanoparticles, that which results in lower temperatures of water desorption and glass transition temperature depression.
Keywords: PVA/fumed silica; PVA adsorption; Textural characteristics; Broadband dielectric relaxation spectroscopy; Thermally stimulated depolarization current; Infrared spectra
The adsorption of phosphate from an aquatic environment using metal-loaded orange waste
by Biplob Kumar Biswas; Katsutoshi Inoue; Kedar Nath Ghimire; Shingo Ohta; Hiroyuki Harada; Keisuke Ohto; Hidetaka Kawakita (pp. 214-223).
Phosphate removal from an aquatic environment was investigated using La(III)-, Ce(III)- and Fe(III)-loaded orange waste. The adsorption isotherm, the kinetics of adsorption and the effect of pH on the removal of phosphate have been examined. The % removal of phosphate using La(III)- and Ce(III)-loaded orange waste gel increases with increasing pH within the range of 5–7 but decreases when the pH is increased beyond this range. The equilibrium sorption was observed to be in accordance with Langmuir type adsorption and the maximum adsorption capacity was evaluated as 13.94 mg P/g of dry gel for all the three types of gels. Kinetic studies revealed that 15 h is enough to reach equilibrium in batch experiments. Fixed bed sorption experiments confirmed the continuous phosphate adsorption and elution capability of such simply modified gels. Due to their low cost, availability and significantly high adsorption capability, metal-loaded SOW gels can be effectively employed for the removal of phosphate from water.Effective removal of phosphate has been investigated using three different metal-loaded orange waste gels, which provided a treatment provision at wider pH range from phosphorus contaminated aquatic environment.
Keywords: Phosphate; Orange waste; Metal-loaded gel; Ligand substitution; Adsorption
Sorption of silicates on goethite, hematite, and magnetite: Experiments and modelling
by Norbert Jordan; Nicolas Marmier; Claire Lomenech; Eric Giffaut; Jean-Jacques Ehrhardt (pp. 224-229).
Sorption of H4SiO4 (including experiments as a function of time,Kd measurement with differentm/v ratios and sorption edges) onto different iron (hydro)oxides as goethite ( α-FeOOH), hematite ( α-Fe2O3), and magnetite (Fe3O4) has been studied with concentration of silicates under solubility limit. A surface complexation model has been used to account for sorption edge of silicates onto these iron oxide surfaces. It reveals that two types of surface complex namelyFeH3SiO4 andFeH2SiO−4, are needed to describe properly the experimental observations.This figure represents experimental sorption edges of H4SiO4 on goethite, hematite, and magnetite, as well as calculations done with DDL model to accounts for the experimental observations.
Keywords: Silicates; Sorption; Iron oxides; Surface complexation model
Temperature effects on the surface acidity properties of zirconium diphosphate
by N. Finck; R. Drot; F. Mercier-Bion; E. Simoni; H. Catalette (pp. 230-236).
As part of the temperature effects study on the sorption of metallic cations onto zirconium diphosphate, we have first investigated the intrinsic surface properties of this synthetic compound for different temperatures (25, 50, 75 and 90 °C). A physico-chemical study (IR, XRD) assessed its purity, and the measured N2-BET specific area was13.4±0.2 m2g−1. Mass and potentiometric titrations showed that the experimental point of zero charge (pHpzc=2.6±0.2) and the surface site density remained constant between 25 and 90 °C. The potentiometric titration data were simulated with the constant capacitance model, considering two reactive surface sites, with a total surface site density equal to7.2 sitesnm−2. The intrinsic protonation and deprotonation constants were found to increase with the temperature, as well as the calculated apparent constants. The simulation results showed that the capacitance increased with the temperature. The proportions of the neutral, protonated and deprotonated forms for each site type were quantified thermodynamically by application of the Van't Hoff relation.The variation of the surface acidity constants of ZrP2O7 have been calculated from the simulation of the potentiometric data, using a surface complexation model (CCM). The endothermic character is clearly evidenced as the plotted constants increase with temperature.
Keywords: Surface properties; Zirconium diphosphate; Temperature; Speciation; Modeling; Thermodynamic analysis
New insights into the structure of polyelectrolyte complexes
by Linda Gärdlund; Lars Wågberg; Magnus Norgren (pp. 237-246).
The formation of polyelectrolyte complexes (PECs) from oppositely charged linear polyelectrolytes (PELs) was studied using static light scattering at various salt concentrations. The PELs used were poly(allylamine hydro chloride) (PAH) and the two polyanions poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA). Physical characteristics such as the radii of gyration, molecular weights, and water contents of the PECs were determined at various molar mixing ratios. Despite relatively small differences in chemical structure between PAA and PMAA, fairly large differences were detected in these physical characteristics. Generally, PECs comprising PMAA were larger and contained more water. Moreover, by using cryogenic transmission electron microscopy, transmission microscopy and atomic force microscopy, shape and structure of the prepared PECs were investigated both in solution and after drying. The PECs were found to be spherical in solution and the shape was retained after freeze-drying. PECs adsorbed on silica surfaces and dried in air at room-temperature still showed a three-dimensional structure. However, the relatively low aspect ratios indicated that the PECs collapsed significantly due to interactions with the silica during adsorption and drying. At intermediate ionic strengths (1–10 mM), stagnation point adsorption reflectometry (SPAR) showed that the adsorption of low charged cationic PAH–PAA PECs on silica surfaces increased if the pH value was increased from pH 5.5 to 7.5.
Keywords: Polyelectrolyte complex; Poly(acrylic acid); Poly(methacrylic acid); Poly(allylamine hydro chloride); Structure; Water content; Cryo-TEM; AFM; Light scattering
Electrospray in the dripping mode for cell microencapsulation
by Jingwei Xie; Chi-Hwa Wang (pp. 247-255).
Entrapment of living cells in microbeads is to protect the encapsulated cells from the host's immune system, which can be used as drug delivery vehicles, immunotherapies and engineered tissues. The main objective of the present study was to investigate the droplet formation and to better develop mono-dispersed microencapsulation of living cells with controllable size. The uniformity of microencapsulation size was realized by performing electrospray in the dripping mode and also stabilized by an additional ring electrode. Reduction of droplet diameter and increase in the dripping frequency were observed with increasing applied voltage to the nozzle using a conventional electrospray setup. The vibration of the needle was found to reduce when high voltage was applied to the nozzle. With increasing voltage applied to the ring electrode, the dripping frequency was found to decrease with the formation of slightly larger sizes of droplets. Hep G2 cell line was taken as the model cell line for encapsulation in calcium alginate microbeads. Relatively uniform microbeads could be achieved when operating under low flow rates with high voltages applied to the nozzle by using a conventional electrospray setup. In contrast, uniform microbeads can not be obtained using a similar setup under high flow rates unless the ring electrode is applied with voltage to stabilize the electrospray in the dripping mode. In this modified electrospray, microbeads with narrow size distribution and slightly larger size can be obtained even for cases under high flow rates. Phase contrast microscope images showed that the diameter of microbeads from around 200 μm to 2 mm could be finely tuned by adjusting various operating parameters.Relatively uniform microbeads could be achieved by using an electrospray setup under low liquid flow rates. Microbeads with narrow size distribution and slightly larger size can be obtained even for cases under high flow rates by performing electrospray in the dripping mode and also stabilized by an additional ring electrode.
Keywords: Electrospray; Dripping; Droplet formation; Microencapsulation
Dielectric analysis of chitosan gel beads suspensions: Influence of low crosslinking agent concentration on the dielectric behavior
by Ni Ni; Kongshuang Zhao (pp. 256-264).
Dielectric measurements were carried out for the suspensions of chitosan gel beads (CGB) crosslinked with glutaraldehyde (GA), ranging in crosslinking time from 1 to 180 min at six fixed low GA concentrations over a frequency range from 40 to 110 MHz. The distinct dielectric relaxations observed in the frequency range of 104–105 Hz were explained by the effects of the interfacial polarization. By fitting the experimental data with Cole-Cole equation the dielectric parameters of the suspensions were obtained, and the phase parameters were calculated using Hanai's method. The influence of crosslinking on the dielectric spectra of CGB was investigated by viewing the crosslinking time dependencies of conductivity increment (Δ κ), relaxation frequency (f0), permittivity of CGB (εi), conductivity of CGB (κi) and conductivity of continuous media (κa) at six fixed GA concentrations. Some information were gained, such as, thinner electric double layer, particle with rougher surface and more compact gel backbone with increasing crosslinking time. The basic information obtained can provide valuable references for the preparation of CGB and the application to more extensive fields such as controlled-release technology of medicament.Three-dimensional representations of the crosslinking time dependency of (a) the permittivity spectrum and (b) the conductivity spectrum for the suspensions of CGB crosslinked at GA concentration of 0.300% for different crosslinking times. Theε/κ axis is linear andf/t axis is logarithmic.
Keywords: Dielectric analysis; Suspensions of chitosan gel beads; Low GA concentration; Hanai's method
A new design strategy for dispersion stabilization of Ni particles based on the surface acid and base properties of Ni particles
by Sangkyu Lee; Seon-Mi Yoon; Jae-Young Choi; Ungyu Paik (pp. 265-271).
A dispersion technology for Ni particles suspended in a non-aqueous medium based on the quantitative evaluation of surface acid–base properties of Ni particles is described. A quantitative analysis of surface acid–base properties of Ni particles was performed using non-aqueous titration. Dimethylamino ethanol and acetic acid were used as probe molecules to detect surface acid–base amounts of Ni particles. The dispersion system was designed on the basis of the amounts of surface acid–base sites on the Ni particle surface. Rheological behavior and agglomerate particle size data demonstrate that the dispersion stability of the designed Ni suspension is markedly improved, as expected. Therefore, the design strategy to improve the dispersion stability of Ni particles was successful. This strategy is expected to be applicable to dispersion systems of other particles suspended in a non-aqueous medium.
Keywords: Design; Dispersion system; Dispersion stability; Non-aqueous; Surface acid–base properties; Ni particle
Formation of solid and hollow cuprous oxide nanocubes in water-in-oil microemulsions controlled by the yield of hydrated electrons
by Qingde Chen; Xinghai Shen; Hongcheng Gao (pp. 272-278).
A local ordered structure constructed from solid Cu2O nanocubes was obtained by the radiolytic reduction of Cu(NO3)2 in a water-in-oil (W/O) microemulsion composed of Triton X-100, n-hexanol, cyclohexane, and water in the presence of ethylene glycol (EG). However, when Triton X-100 was replaced with Brij 56 in the microemulsion, hollow Cu2O nanocubes were synthesized. The addition of toluene into the Brij 56 system could decrease the ratio of hollow nanocubes. It was suggested that the balance between the reduction rate of Cu2+ depending on the yield of hydrated electrons (e−aq) and the escape rate of the mixed solvent determined their final morphologies. The presence of EG influenced the rigidity of the interface of the microemulsion and thus the above balance, which resulted in the different morphologies of Cu2O nanoparticles in the Brij 56-based microemulsion.A local ordered structure constructed from solid Cu2O nanocubes was obtained by the radiolytic reduction of Cu(NO3)2 in a W/O microemulsion composed of Triton X-100, n-hexanol, cyclohexane, and water in the presence of ethylene glycol. However, when Triton X-100 was replaced with Brij 56 in the microemulsion, hollow Cu2O nanocubes were synthesized. Our results suggested that the yield of hydrated electrons plays an important role.
Keywords: Cuprous oxide; Nanocubes; γ; -Irradiation; Hydrated electrons; Microemulsion
Dispersion of alumina suspension using comb-like and diblock copolymers produced by RAFT polymerization of AMPS and MPEG
by H. Bouhamed; S. Boufi; A. Magnin (pp. 279-291).
Different copolymers of 2-acrylamido-2-methylpropanesulfonic acid sodium salt (AMPS) methoxypolyethyleneglycol methacrylate (MPEG) with statistical and diblock distributions were prepared using RAFT-controlled radical polymerization. The effect of polymer architecture and monomer ratio on the adsorption behavior, electrokinetic, and stability properties of the alumina suspensions was investigated. Adsorption isotherms showed that copolymer interaction depended on both the ratio of the monomers and their distribution within the macromolecular backbone. Changes in the electrokinetic properties of the alumina suspension after addition of the copolymers were investigated by monitoring the particle ζ-potential as a function of pH. A continuous shift in the isoelectric point IEP to a more acidic value was observed and particle charges were reversed when the amount of copolymer added exceeded a critical level.Schematic illustration of the AMPS-block copolymer at the surface of alumina particles in aqueous medium and over a pH range 4–9. The charged AMPS block is responsible of the copolymer adsorption giving rise to a high surface charge that enhance colloidal stability.
Keywords: Adsorption; Copolymer; Stability; RAFT
Electrochemical removal of the hazardous dye Reactofix Red 3 BFN from industrial effluents
by Vinod Kumar Gupta; Rajeev Jain; Shaily Varshney (pp. 292-296).
The electrochemical treatment of dyestuff from aqueous solution using an iron cell was achieved with reduction in chemical oxygen demand (COD) and color with high efficiency. Degradation of the azo dye Reactofix Red 3 BFN was carried out under different experimental conditions. Electrolysis completely decolorizes the effluent with substantial reduction in COD value. The rate kinetics during electrolysis was found to be first order. Results show that electrochemical reduction is a superior technology for treatment of dyes, as there is no simultaneous addition of anions, such as sulfate or chloride.Cyclic voltammograms of Reactofix Red 3 BFN,5.0×10−5 M at pH 3.0: (a) before electrolysis, (b) after electrolysis.
Keywords: Reactofix Red 3 BFN; Electrolysis; Cyclic voltammetry; Kinetics; COD
Modeling the acid–base surface chemistry of montmorillonite
by Ian C. Bourg; Garrison Sposito; Alain C.M. Bourg (pp. 297-310).
Proton uptake on montmorillonite edge surfaces can control pore water pH, solute adsorption, dissolution kinetics and clay colloid behavior in engineered clay barriers and natural weathering environments. Knowledge of proton uptake reactions, however, is currently limited by strong discrepancies between reported montmorillonite titration data sets and by conflicting estimates of edge structure, reactivity and electrostatics. In the present study, we show that the apparent discrepancy between titration data sets results in large part from the widespread use of an erroneous assumption of zero specific net proton surface charge at the onset of titration. Using a novel simulation scheme involving a surface chemistry model to simulate both pretreatment and titration, we find that montmorillonite edge surface chemistry models that account for the “spillover” of electrostatic potential from basal onto edge surfaces and for the stabilization of deprotonated AlSi bridging sites through bond-length relaxation at the edge surface can reproduce key features of the best available experimental titration data (the influence of pretreatment conditions on experimental results, the absence of a point of zero salt effect, buffer capacity in the acidic pH range). However, no combination of current models of edge surface structure, reactivity and electrostatics can quantitatively predict, without fitted parameters, the experimental titration data over the entire range of pH (4.5 to 9) and ionic strength (0.001 to 0.5 mol dm−3) covered by available data.
Keywords: Montmorillonite; Smectite; Acid–base properties; Potentiometric titration; Surface complexation model
Preparation of hexagonal platy particles of nanoporous silica using hydrotalcite as morphology template
by Naoki Shimura; Makoto Ogawa (pp. 311-316).
Hexagonal platy composite particles with a hydrotalcite core and a nanoporous silica shell with a thickness of ca. 100 nm were synthesized by the reaction of a Mg–Al hydrotalcite with a homogeneous aqueous solution containing tetraethoxysilane, hexadecyltrimethylammonium chloride, ammonia and methanol at 3 °C. The calcination of the products at 500 °C in air led to the composite particle with a Mg/Al mixed oxide core and a nanoporous silica shell. Hexagonal platy particles of nanoporous silica with a pore diameter of 2.3 nm and BET surface area of 700 m2 (g of silica)−1 were obtained by removing the Mg/Al mixed oxide core.Hexadecyltrimethylammonium cation–silica layers were deposited on a Mg–Al hydrotalcite. A nanoporous silica–Mg/Al oxide composite was obtained by calcination. Nanoporous silica hollow platy particles, which replicated the morphology of hydrotalcite, were obtained by dissolution of the hydrotalcite core.
Keywords: Nanoporous silicas; Core shell particles; Hydrotalcite; Supramolecular templating approach
Interaction between organic vapors and clinoptilolite–mordenite rich tuffs in parent, decationized, and lead exchanged forms
by M.P. Elizalde-González; M.A. Pérez-Cruz (pp. 317-325).
Scientific interest in adsorption phenomena of organic vapors has concentrated on synthetic zeolites. Solid–vapor systems containing natural zeolites deserve special attention due to their abundance and environmental applications. Adsorption thermodynamic characteristics for benzene, toluene, n-hexane, and CCl4 were measured on clinoptilolite-rich zeolitic tuffs from Mexico (ZE) and Hungary (ZH) on parent, decationized, dealuminated, and lead-exchanged samples. The clinoptilolite structure released Na+ and Ca2+ by acid treatment and this was accompanied by dealumination to a greater extent on ZE than on ZH. The exchange isotherm of Pb2+ on ZE exhibited a concave type “a” form and accomplished 95% exchange and the tuff was selective atXi(s)<0.25. The pattern of adsorption isotherms was the same on all tuffs: benzene>toluene> n-hexane>carbon tetrachloride. The−ΔH¯ values were higher for toluene than for the other adsorbates. Curves ofqisost vs coverage decreased with the increment of the adsorbed amount in practically all studied systems. The contributions to the solid–vapor interaction potential were examined using inverse gas chromatography. The specific interaction energyGsp was primarily due to adsorbate–framework and adsorbate–cation interactions at low adsorbate pressures producing low surface coverage.By using inverse gas chromatography, adsorption thermodynamic characteristics for the nonpolar organic adsorbates: benzene, toluene, n-hexane, and CCl4 were measured on clinoptilolite-rich zeolitic tuffs. The contributions to the solid–vapor interaction were examined on parent (Z), decationized-dealuminated (Z-Al), and lead-exchanged (Z+Pb) samples. Curvesqisost vs coverage decreased with the increment of the adsorbed amount. The specific interaction energy was primarily due to adsorbate–framework and adsorbate–cation interactions.
Keywords: Clinoptilolite; Dealumination; Decationization; Ion exchange; Lead; Specific interaction energy; Inverse gas chromatography
Octadecylsilane hybrid silicas prepared by the sol–gel method: Morphological and textural aspects
by Rodrigo Brambilla; Gilvan P. Pires; João H.Z. dos Santos; Márcia S. Lacerda Miranda (pp. 326-332).
A series of octadecylsilane-modified silicas was prepared by the sol–gel method through the hydrolysis and cocondensation of tetraethylorthosilicate (TEOS) with octadecyltriethoxysilane (ODS). The ODS:TEOS ratio was varied between 0:100 and 100:0. The resulting carbon content was between 2.5 and 53.4%. In the case of pure ODS, the resulting silica presented 68.6% of C. Hybrid silicas were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, and29Si nuclear magnetic resonance spectroscopy. Spheres of ca. 0.5–1.0 μm were obtained in the case of hydrolysis of pure TEOS. The combination of ODS:TEOS ratio yielded systems combining spherical and lamellar patterns zones. Monitoring the particle growth, it seems that spherical particles grow around lamellar zones, these latter concentrating the organosilicon moieties. The degree of cross-linking of ODS moieties was shown to be dependent on the ODS addition time and stirring speed.The effect of TEOS/ODS ratio, of the addition time and stirring speed on surface coverage, and on morphological and textural characteristics of the resulting hybrid materials was evaluated. Hybrid silica changed from totally spherical morphology to lamellar domains as the ODS amount was increased.
Keywords: Hybrid silica; Sol–gel; Octadecylsilane; ODS
Detachment of liquid droplets from fibres—Experimental and theoretical evaluation of detachment force due to interfacial tension effects
by Benjamin J. Mullins; Andreas Pfrang; Roger D. Braddock; Thomas Schimmel; Gerhard Kasper (pp. 333-340).
The detachment of barrel-shaped oil droplets from metal, glass and polymer fibres was examined using an atomic force microscope (AFM). The AFM was used to detach the droplets from the fibres while measuring the force–distance relationship. A novel fibre–droplet interfacial tension model was applied to predict the force required to draw the droplet away from its preferential axisymmetric position on the fibre, and also to predict the maximal force required to detach the droplet. The model assumes that the droplet retains a spherical shape during detachment, i.e., that droplet distortion is negligible. This assumption was found to be reasonably accurate for small radius oil droplets (<10 μm), however less accurate for larger droplets (>25 μm). However, it was found that the model produced a good agreement with the maximal detachment force measured experimentally—regardless of droplet size and degree of deformation—even though the model could not predict droplet extension beyond a length of one droplet radius.The detachment force of liquid droplets from fibres was measured experimentally using an AFM, and compared with simulated results from a novel interfacial tension model.
Keywords: Droplet; Fibre; Atomic force microscope (AFM); Interfacial tension; Capillary bridge
Investigations of drop impact on dry walls with a lattice-Boltzmann model
by Shiladitya Mukherjee; John Abraham (pp. 341-354).
In this work, axisymmetric computations of drop impingement on dry walls are presented. The two-phase model employed is an axisymmetric lattice-Boltzmann model. Computations are performed in the parametric range of Weber number We of 7 to 8770, Ohnesorge number Oh of 0.02 to 0.137, and drop–wall equilibrium contact angleθeq of 35° to 150°. Deposition and rebound outcomes are reported. In deposition, the different stages of drop evolution including spread, recoil and equilibration are reproduced and studied. Comparisons made with experimentally reported data of temporal evolution of the spread factor and the dynamic evolution of the contact angle show good agreement. Rebound is observed on non-wetting surfaces. The transition between deposition and rebound is shown to be influenced by the impact We, Oh, and advancing and receding static contact angles. Apart from impingement outcomes, the influence of We and Oh on the dynamic contact angle is investigated.Spreading, recoil, and rebound outcomes after a drop impacts on a dry wall are studied.
Keywords: Drop impact; Dynamic contact angle; Lattice-Boltzmann method; Drop spread; Drop recoil
Microstructure and structural transition in coconut oil microemulsion using semidifferential electroanalysis
by Chunsheng Mo; Xiaoge Li (pp. 355-362).
The microemulsification in coconut oil/octadecyltrimethylammonium bromide/iso-pentanol/water system is investigated. The effect of iso-pentanol concentrations on the size of single-phase microemulsion region is discussed. It is found that the maximum microemulsion domain is obtained when cosurfactant (iso-pentanol)-to-surfactant (octadecyltrimethylammonium bromide) mass ratio is 1.5. The diffusion coefficients of ferrocene (electroactive probe) in microemulsion microenvironment are measured by semidifferential electroanalysis. The microstructure and structural transition from water-in-oil to oil-in-water microemulsions through a bicontinuous structure is examined. The results are found to be in agreement with that of conductivity measurements.The formation of microemulsion(μE) with high water content in coconut oil/octadecyltrimethylammonium bromide/iso-pentanol/water system (A) and diffusion coefficient of ferrocene in μE medium obtained by semidifferential electroanalysis method as function of water content (B), the microstructure and structural transition from water-in-oil to oil-in-water microemulsions through a bicontinuous structure was examined.
Keywords: Semidifferential electroanalysis; Octadecyltrimethylammonium bromide; Coconut oil; Conductivity; Diffusion coefficient
Emulsification in turbulent flow
by Nina Vankova; Slavka Tcholakova; Nikolai D. Denkov; Ivan B. Ivanov; Vassil D. Vulchev; Thomas Danner (pp. 363-380).
Systematic experimental study of the effects of several factors on the mean and maximum drop sizes during emulsification in turbulent flow is performed. These factors include: (1) rate of energy dissipation, ε; (2) interfacial tension, σ; (3) viscosity of the oil phase,ηD; (4) viscosity of the aqueous phase,ηC; and (5) oil volume fraction, Φ. The emulsions are prepared by using the so-called “narrow-gap homogenizer” working in turbulent regime of emulsification. The experiments are performed at high surfactant concentration to avoid the effect of drop–drop coalescence. For emulsions prepared in the inertial turbulent regime, the mean and the maximum drop sizes increase with the increase ofηD and σ, and with the decrease of ε. In contrast, Φ andηC affect only slightly the mean and the maximum drop sizes in this regime of emulsification. These results are described very well by a theoretical expression proposed by Davies [Chem. Eng. Sci. 40 (1985) 839], which accounts for the effects of the drop capillary pressure and the viscous dissipation inside the breaking drops. The polydispersity of the emulsions prepared in the inertial regime of emulsification does not depend significantly on σ and ε. However, the emulsion polydispersity increases significantly with the increase of oil viscosity,ηD. The experiments showed also that the inertial turbulent regime is inappropriate for emulsification of oils with viscosity above ca. 500 mPa s, if drops of micrometer size are to be obtained. The transition from inertial to viscous turbulent regime of emulsification was accomplished by a moderate increase of the viscosity of the aqueous phase (above 5 mPa s in the studied systems) and/or by increase of the oil volume fraction,Φ>0.6. Remarkably, emulsions with drops of micrometer size are easily formed in the viscous turbulent regime of emulsification, even for oils with viscosity as high as 10,000 mPa s. In this regime, the mean drop size rapidly decreases with the increase ofηC and Φ (along with the effects of ε, σ, andηD, which are qualitatively similar in the inertial and viscous regimes of emulsification). The experimental results are theoretically described and discussed by using expressions from the literature and their modifications (proposed in the current study).Transition from inertial to viscous regime of turbulent emulsification is induced by increasing the viscosity of the continuous phase and/or the oil volume fraction. Much smaller drops are obtained in the viscous regime of emulsification.
Keywords: Emulsification in turbulent flow; Drop breakup; Drop-size distribution; Emulsification in viscous regime; Kolmogorov theory of emulsification
Emulsions stabilised by food colloid particles: Role of particle adsorption and wettability at the liquid interface
by Vesselin N. Paunov; Olivier J. Cayre; Paul F. Noble; Simeon D. Stoyanov; Krassimir P. Velikov; Matt Golding (pp. 381-389).
We study the effect of the particle wettability on the preferred type of emulsion stabilised solely by food colloid particles. We present results obtained with the recently developed gel trapping technique (GTT) for characterisation of wettability and surface structuring of individual food colloid particles adsorbed at air–water and oil–water interfaces. This method allows us to replicate a particle monolayer onto the surface of polydimethylsiloxane (PDMS) without altering the position of the particles. By observing the polymer surface with scanning electron microscopy (SEM), we are able to determine the contact angle of the individual particles at the initial liquid interface. We demonstrate that the GTT can be applied to fat crystal particles, calcium carbonate particles coated with stearic acid and spray-dried soy protein/calcium phosphate particles at air–water and oil–water interfaces. Subsequently, we prepare emulsions of decane and water stabilised by the same food colloid particles and correlate the wettability data obtained for these particles to the preferred type of emulsions they stabilise.SEM image of soy protein particles replicated from oil–water interface by a gel trapping technique for studying the effect of their wettability on the preferred type of emulsions they stabilise.
Keywords: Food particles; Solid-stabilised emulsions; Fat crystals; Wettability; Contact angle
Micellization in aqueous solution of an ethylene oxide–propylene oxide triblock copolymer, investigated with1H NMR spectroscopy, pulsed-field gradient NMR, and NMR relaxation
by Junhe Ma; Chen Guo; Yalin Tang; Junfeng Xiang; Shu Chen; Jing Wang; Huizhou Liu (pp. 390-396).
1H nuclear magnetic resonance (NMR) spectroscopy has been applied to study the temperature and concentration-induced micellization of a poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) triblock copolymer, Pluronic P105, in D2O solutions in the temperature range from 5 to 45 °C and the concentration range from 0.01 to 15% (w/v). The intrinsic probes, the chemical shift, and the half-height width of the POCH3 signal are very sensitive to the local environment and can be used to characterize the temperature and concentration-dependent aggregation process. When the temperature approaches the critical micellization temperature or the polymer concentration reaches the critical micellization concentration, the chemical shift of the POCH3 signal moves toward lower ppm values and the half-height width of the POCH3 signal shows a sudden increase. It indicates that the methyl groups are experiencing a progressively less polar environment and transferring from water to the hydrophobic micellar core. The hydrodynamic radius of the unimers and the micelles are determined as be 1.8 and 5.0 nm by means of pulsed-field gradient spin-echo (PGSE) NMR. They were independent of temperature and concentration. The drastic shortening of spin–lattice relaxation timeT1 for the POCH3/CH2 protons in the transition region suggested that the PPO blocks are located in a “liquid-like” micellar core, whereas the exponential increase ofT1 for the PEOCH2 protons implied that the PEO blocks are still keeping in contact with surrounding water. Thermodynamics analysis according to a closed association model shows that the micellization process is entropy-driven and has an endothermic micellization enthalpy.(a) Overall1H NMR spetra of 1% Pluronic P105 in D2O solution recorded at 5 °C; (b) Stack plot of POCH3 signal in1H NMR spectra at various temperatures.
Keywords: PEO–PPO–PEO triblock copolymer; Micellization; 1; H NMR; Diffusion NMR; NMR relaxation
Synthesis and amphiphilic properties of decanoyl esters of tri- and tetraethylene glycol
by Ying Zhu; Valérie Molinier; Sébastien Queste; Jean-Marie Aubry (pp. 397-404).
Well-defined decanoyl triethylene glycol ester and decanoyl tetraethylene glycol ester were synthesized and compared to their ether counterparts (C10E4 and C10E3). Their physicochemical properties i.e. critical micelle concentrations (CMC), cloud points, and equilibrium surface tensions were determined. Binary water–surfactant phase behavior was also studied by polarized optical microscopy. The stability of the ester bond was determined by investigating alkaline hydrolysis of the compounds. It was found that CMC, cloud point and equilibrium surface tension are roughly the same for corresponding ethers and esters. In the binary diagram, the esters form only lamellar phases, the area of which is smaller than that of the ether counterparts. These different behaviors can be related to the modification of the molecular conformation induced by the replacement of the ether group by the ester group.Two pure decanoyl esters of tri- and tetraethylene glycol were synthesized. Their amphiphilic properties are similar to their ether counterparts with reduced liquid crystalline regions due to hindered molecular packing.
Keywords: Nonionic surfactants; Monoester of polyethylene glycol; Binary phase diagram; Packing parameter; Alkaline hydrolysis
ESR study of aqueous micellar solutions of perfluoropolyether surfactants with the use of fluorinated spin probes
by Ewa Szajdzinska-Pietek; Konrad Sulak; Ileana Dragutan; Shulamith Schlick (pp. 405-412).
Fluoroalkyl esters of 3-carboxy pyrroline nitroxide, FP n (n=8 and 12), containing (n−2) CF2 groups in the side-chain, were used as novel ESR spin probes of fluorinated micellar systems. The method was applied to study aqueous solutions of perfluoropolyether surfactants of the general formula Cl(C3F6O)2CF2COOX, consisting of two perfluoroisopropoxy units and the counterion X = Na+ or NH+4. By measuring the change of14N hyperfine splitting with surfactant concentration the critical micellar concentration of the ammonium salt was determined at temperatures of 297, 313 and 333 K. The ESR line shape was also examined as a function of surfactant concentration and of temperature in the range 120–360 K. The results are discussed in terms of solubilization and local environment of the probes in micelles of different size and shape, depending on the surfactant concentration and the kind of the counterion.Pyrroline nitroxide derivatives with a fluorinated side-chain are suitable spin probes for CMC determination of fluorinated surfactants, and their ESR spectra are sensitive to changes of the micellar structure.
Keywords: Perfluoropolyether surfactants; Micellar solutions; ESR spectroscopy; Fluorinated spin probes
Enhanced stability of short- and long-chain diselenide self-assembled monolayers on gold probed by electrochemistry, spectroscopy, and microscopy
by S. Subramanian; S. Sampath (pp. 413-424).
Well-ordered, compact, self-assembled monolayers (SAMs) of hexyl and dodecyl diselenides have been formed on oriented (111) gold surfaces. Monolayer formation has been effected by adsorption from neat diselenides as well as millimolar solutions of diselenides in alcohol. The monolayer formation is confirmed using electrochemical quartz crystal microbalance studies. The stability and permeability of the monolayers at various temperatures have been probed using reflection absorption infrared spectroscopy (RAIRS) and electrochemistry. The RAIRS studies in the dry state show the formation of highly ordered, compact structures when adsorbed from neat compounds compared to the monolayers adsorbed in the presence of alcohol. The monolayers adsorbed from neat diselenide are quite stable as a function of temperature irrespective of the chain length. The electrochemical studies based on the blocking behavior of the monolayers toward electron transfer between a diffusing species and the electrode surface reflect the stability and the compactness of the structure. The results point out that the presence of solvent molecules during the SAM formation hinders the organization of the monolayer structure, especially in the case of short-chain diselenide monolayers.Well ordered short-chain selenide monolayers on Au(111).
Keywords: Self-assembled monolayer; Diselenides; Infrared spectroscopy; Electrochemistry; Thermal stability; Short and long chain surfactants
The aqueous catanionic system sodium perfluorooctanoate–dodecyltrimethylammonium bromide at low concentration
by José Luis López-Fontán; Elena Blanco; Juan M. Ruso; Gerardo Prieto; Pablo C. Schulz; Félix Sarmiento (pp. 425-431).
The interaction between sodium perfluorooctanoate (SPFO) and dodecyltrimethylammonium bromide (DTAB) was studied by several methods and it was found strongly synergistic. Above a mole fraction of SPFO in the surfactant mixture(αSPFO)=0.38, the interaction is repulsive and increases with the content of SPFO in both, the overall mixture and micelles, whereas the interaction is attractive if DTAB is in excess. AtαSPFO=0.38 the low miscibility between hydrocarbon and fluorocarbon is counterbalanced by the electrostatic attraction between the opposite charged head groups, and the micelle composition is ideal (i.e., the mole fraction of SPFO in micellesXSPFO=αSPFO=0.38). The solubility of fluorocarbon in hydrocarbon is lower than that of hydrocarbon in fluorocarbon. Micelles of DTAB act as a solvent for SPFO without important structural changes, whilst micelles of SPFO undergo important changes when dissolve DTAB. This asymmetry may be interpreted as caused by the difference in chain length that favors the inclusion of the shorter chain in micelles of the longer surfactant, but disfavors the opposite process. AboveXSPFO=0.5 there is an excess adsorption of bromide ions on the mixed micelles surface, giving rise to a high ζ potential. Micelles of pure SPFO or pure DTAB show an important energy barrier which prevents micelle flocculation. The inclusion of SPFO in DTAB micelles produces a reduction of the energy barrier, which disappeared whenαSPFO=0.5. This produces the flocculation of micelles giving rise to the formation of a non-birefringent coacervate, which is probably formed by unordered isometric clusters of micelles.The DLVO energy if interaction between micelles as a function of the shortest intermicellar distance betweenαSPFO=0 andαSPFO=0.5 at the CMC.
Keywords: Fluorocarbon/hydrocarbon mixed surfactants; Catanionic surfactants; Coacervate; Sodium perfluorooctanoate; Dodecyltrimethylammonium bromide
The interface engine: Experimental consequences
by Klaus Tauer; Steffen Kozempel; Gudrun Rother (pp. 432-438).
A light microscopy study confirms spontaneous emulsification at the quiescent, thermally equilibrated interface between pure oil and pure water during the chemical equilibration period. The process is qualitatively explained within the frame of the classical nucleation theory assuming a mixed interface layer between the two liquids in contact allowing supersaturation.Light microscopy image of the interface between pure tert-butylstyrene and pure water. Droplets formation occurs spontaneously triggered by the composition of the interfacial layer.
Keywords: Spontaneous emulsification; Pure water and pure oil; Interface layer; Light microscopy
Copper- and ligand-free Sonogashira reaction catalyzed by palladium in microemulsion: Effects of surfactant and alcohol
by Jian-Zhong Jiang; Yan-An Wei; Chun Cai (pp. 439-443).
A rapid copper- and ligand-free Sonogashira reaction was performed in an oil-in-water microemulsion. Palladium nanoparticles can be in situ formed in the microemulsion without other reductants. The microemulsion containing in situ-formed nano-Pd is an efficient system for the Sonogashira reaction. The reactions were faster in the microemulsion than in micelles. The effects of surfactant, alcohol, and temperature are discussed. Excellent yield of the Sonogashira reaction catalyzed by 0.5 mol% palladium could be achieved at 80 °C within 2 min.Copper- and ligand-free Sonogashira reaction catalyzed by 0.5 mol% in situ-formed palladium nanoparticles was achieved at 80 °C within 2 min in an oil-in-water microemulsion.
Keywords: Microemulsion; Palladium; Sonogashira reaction
Cationic ester-containing gemini surfactants: Chemical hydrolysis and biodegradation
by A.R. Tehrani-Bagha; H. Oskarsson; C.G. van Ginkel; K. Holmberg (pp. 444-452).
Two cationic gemini surfactants having ester bonds between the hydrophobic tail and the cationic moiety have been synthesized. The ester bonds were either with the ester carbonyl group away from the positive charge (esterquat type arrangement) or facing the positive charge (betaine ester type arrangement). The chemical hydrolysis of the surfactants was investigated and compared with the hydrolysis of the corresponding monomeric surfactants. The betaine ester type of surfactants was found to hydrolyze much faster than the esterquat surfactants. It was also seen that above the critical micelle concentration the gemini surfactants were much more susceptible to alkaline hydrolysis than the corresponding monomeric surfactants. The biodegradation of the geminis and the monomeric surfactants were also studied. It was found that whereas the monomeric surfactants were rapidly degraded, the two gemini surfactants were more resistant to biodegradation and could not be classified as readily biodegradable. The 60% biodegradation was reached after 35–40 days. Thus, there was no correlation between rate of chemical hydrolysis and rate of biodegradation.Base catalyzed hydrolysis of a gemini alkyl betainate surfactant may be accelerated through a neighboring group participation mechanism.
Keywords: Gemini surfactants; Synthesis; Biodegradation; Esterquats; Hydrolysis; Cleavable
Micellar induced regioselectivity in the two-step consecutive reaction of SO2−3 with Br(CH2CH2) nBr (n=2–5)
by Fredrik Currie; Patrik Jarvoll; Krister Holmberg; Laurence S. Romsted; Krishnan Gunaseelan (pp. 453-459).
High field (800 MHz)1H NMR was used to monitor the two-step consecutive reaction of excess SO2−3 with symmetrical bifunctionalα,ω-dibromoalkanes with butane (DBB), hexane (DBH), octane (DBO), and decane (DBD) chains in CTAB micelles at 25 °C. The first-order rate constant for the first substitution step for DBB and DBH is about 5 times faster than for the second, but the kinetics for DBO and DBD were not cleanly first-order. After 40 min, the solution contained about 80% of the intermediate bromoalkanesulfonate from DBB and DBH and the remainder is alkanedisulfonate and unreacted starting material. The same reactions were carried out in homogeneous MeOH/D2O solutions at 50 °C. The rate constants for all fourα,ω-dibromoalkanes were first-order throughout the time course of the reaction and the same within ±10%. However, because micellar solutions are organized on the nanoscale and bring together lipophilic and hydrophilic reactants into a small reaction volume at the micellar interface, they speed this substitution reaction considerably compared to reaction in MeOH/D2O. The CTAB micelles also induce a significant regioselectivity in product formation by speeding the first step of the consecutive reaction more than the second. The results are consistent with the bromoalkanesulfonate intermediates having a radial orientation within the micelles with theCH2SO−3 group in the interfacial region and theCH2Br group directed into the micellar core such that the concentration ofCH2Br groups in the reactive zone, i.e., the micellar interface, is significantly reduced. These results provide the first example of self-assembled surfactant system altering the relative rates of the reaction steps of a consecutive reaction and, in doing so, enhancing monosubstitution of a symmetrically disubstituted species.
Keywords: Cationic surfactant; CTAB; Micelle; Regioselectivity; Nucleophilic substitution
Interfacial aspects of water drop formation at micro-engineered orifices
by Maik J. Geerken; Rob G.H. Lammertink; Matthias Wessling (pp. 460-469).
The formation of emulsions with micro-engineered silicon based arrays of micro-orifices is a relatively new technique. Until now, only the preparation of oil-in-water emulsions was studied due to the hydrophilic nature of silicon. This work evaluates the emulsification of water into n-hexadecane with hydrophobized arrays of micro-orifices. We have studied the drop formation rate, the number of active pores and the drop size. In contrast to conventional macroporous membranes used for membrane emulsification, we observed high dispersed phase fluxes up to 4600 L h−1 m−2 bar−1 while all pores being active at applied pressures below 2 times the critical pressure. The drop diameter was independent from the applied pressure difference. We observed a pressure dependent lag time between drop formations at low emulsification pressures. The lag time is related to the rate of surfactant diffusion to the water–oil interface causing a reduction of the interfacial tension. A significant influence of the used hydrophobization agents, perfluorinated octyltrichlorosilane (FOTS) and octyltrichlorosilane (OTS), was found for the resulting drop sizes and the number of active pores.
Keywords: Emulsification; Micro; Silicon; Interface
Electrokinetically-driven flow mixing in microchannels with wavy surface
by Cha'o-Kuang Chen; Ching-Chang Cho (pp. 470-480).
This paper investigates the mixing characteristics of electrokinetically-driven flow in microchannels with different wavy surface configurations. Numerical simulations are performed to analyze the influence of the wave amplitude and the length of the wavy section on the mixing efficiency within the microchannel. Typically, straight channels have a poor mixing performance because the fluid flow is restricted to the low Reynolds number regime, and hence mixing takes place primarily as a result of diffusion effects. However, the wavy surfaces employed in the current microchannels increase the interfacial contact area between the two species in the microchannel and therefore improve the mixing efficiency. The mixing performance is further enhanced by the application of a heterogeneous charge pattern on the wavy surfaces. The numerical results show that the heterogeneous charge pattern generates flow circulations near the microchannel walls. These circulations are shown to provide an effective enhancement in the mixing performance. Overall, the present results show that the mixing performance is improved by increasing the magnitude of the heterogeneous surface zeta potential upon the wavy surface or by increasing the wave amplitude or the length of the wavy section in the microchannel.The mixing characteristics of electrokinetically-driven flow in microchannels with wavy surface are investigated. The effects of homogeneous and heterogeneous zeta potential applied on the surfaces are discussed in this paper.
Keywords: Electrokinetically-driven flow; Micromixing; Microchannel
Shear-induced structures formed during thixotropic loops in dilute worm-micelle solutions
by Jorge Delgado; Rolando Castillo (pp. 481-488).
The shear stress response of the system CTAB/NaSal/water is studied using strain thixotropic loops in the low concentration regime and[NaSal]/[CTAB]=1. Stress response during up-shear curves depends on the ramping rate. However, stress response during down-shear curves collapses in one curve, no matter the rate used during the ramping down process; it does not depend on the history of the system. In the process of ramping up during the thixotropic loops, the system forms shear-induced structures. We were able to observe them through the scattered light produced by those structures, when the fluid is under shear in the gap of a transparent Couette cell. During the ramping down, the shear-induced structures survive until the shear rate vanishes. Models that describe the form of the up-shear and down-shear curves were presented, as well as, how thixotropic loops can give information about this kind of systems. In particular, for down-shear curves, we can define a decay shear rate constant that follows an Arrhenius temperature dependence.Strain thixotropic loops and images of light scattered from the fluid showing the formation and decay of shear-induced structures in solutions of dilute wormlike micelles.
Keywords: Thixotropic loops; Wormlike micelle; Shear-induced structures; CTAB/salicylate
Wormlike micelles in Tween-80/C mEO3 mixed nonionic surfactant systems in aqueous media
by Dharmesh Varade; Kousuke Ushiyama; Lok Kumar Shrestha; Kenji Aramaki (pp. 489-497).
Formation and rheological behaviour of viscoelastic wormlike micellar solution in aqueous mixed system of nonionic surfactants, polyoxyethylene sorbitan monooleate (Tween-80) and trioxyethylene alkyl ether (C mEO3,m=12, 14, and 16) was studied. The semi-dilute aqueous solution of Tween-80, in presence of C mEO3 shows a sharp increase in viscosity leading to the formation of a gel-like highly viscoelastic solution reaching a maximum, but decreases beyond an intermediate concentration and finally phase separates. When C12EO3 is replaced by C14EO3 the micellar growth occurs more effectively. However, with further increase in alkyl chain length, i.e. with C16EO3, phase separation occurs before a viscoelastic solution is formed. The effect of temperature on the water/Tween-80/C14EO3 mixed surfactant system was also studied. With increase in temperature, viscosity increases more promptly and the viscosity maximum is attained at relatively lower concentration of C14EO3. Enhanced one dimensional micellar growth with increase in the temperature is mainly attributed to the decrease in the spontaneous curvature of the aggregates. Structural investigation by means of small-angle X-ray scattering (SAXS) technique of micelles in aqueous solution of Tween-80 and mixed water/Tween-80/C mEO3 systems confirmed the one dimensional micellar growth in the above system.
Keywords: Tween-80; Rheology; Wormlike micelles; Viscoelasticity; SAXS
Interfacial deposition of Ag on Au seeds leading to AucoreAgshell in organic media
by S. Prathap Chandran; J. Ghatak; P.V. Satyam; Murali Sastry (pp. 498-505).
A seed mediated procedure for the synthesis of hydrophobic AucoreAgshell nanoparticles in toluene is demonstrated. The reaction proceeds by way of the interfacial reduction of silver ions by 3-pentadecylphenol followed by their deposition on hydrophobized Au nanoparticles. Such a hitherto unreported interfacial seeded growth reaction leads to the formation of phase pure AucoreAgshell nanoparticles that retain the hydrophobicity of the seed particles and remain stable in toluene. Such core–shell structures are however not formed in the aqueous phase. The core–shell architecture was verified using TEM analysis and the formation process was studied by recording the UV–vis spectra of the organic phase nanoparticles as a function of time. TEM kinetics also showed gradual increase in the silver layer thickness. Conclusive evidence was however obtained on examination of the HRTEM images of the products formed. Elemental analysis using X-ray photoelectron spectroscopy of the AucoreAgshell nanostructure revealed the presence of metallic silver. Moreover changing the surface capping of the Au seed does not affect the formation of the AucoreAgshell nanostructure.
Keywords: Core–shell nanoparticles; Gold; Silver; Interfacial seeded growth; HRTEM; XPS
Electrostatic assembly and growth of gold nanoparticles in cellulosic fibres
by Ricardo J.B. Pinto; Paula A.A.P. Marques; Manuel A. Martins; Carlos Pascoal Neto; Tito Trindade (pp. 506-512).
Synthetic studies of nanocomposites containing gold nanoparticles attached onto wood or bacterial cellulosic fibres have been performed in situ in the presence of the fibres or by polyelectrolyte-assisted deposition. The optical properties of the final nanocomposites could be tailored not only by the starting Au nanoparticles characteristics but also by the preparative method associated to the type of cellulosic fibres used as the substrate. Thus, gold nanoparticles assembled or generated in situ within cellulosic fibres, are excellent components for long term optical and chemically stable nanocomposites, which appear particularly interesting for security paper applications.Wood or bacterial cellulose fibres were used as the substrates for the preparation of gold nanocomposites. The optical properties of the final gold nanocomposites depend on several parameters which include the type of cellulose used and nanoparticles surface modification procedures. Among other applications, these gold cellulosic nanocomposites seem of particular interest for making security paper products.
Keywords: Nanocomposites; Gold nanoparticles; Cellulose fibres; Bacterial cellulose; Electrostatic assembly
Controlled synthesis of α-Fe2O3 nanorods and its size-dependent optical absorption, electrochemical, and magnetic properties
by Suyuan Zeng; Kaibin Tang; Tanwei Li (pp. 513-521).
Uniform α-Fe2O3 nanorods with diameter of about 30 nm and length up to 500 nm were synthesized by a template-free hydrothermal method and a following calcination of the intermediate product in the air at 500 °C for 2 h. By carefully tuning the concentration of the reactants, a series of α-Fe2O3 nanorods with gradient in aspect ratios can be obtained. The effect of the solvent was also evaluated. Based on the experimental facts, the formation mechanism of this one-dimensional structure was proposed. The size-dependent properties of the as-obtained α-Fe2O3 nanorods were investigated. The optical absorption properties of the samples showed that the band gaps of the samples decreased in the sequence in which the size increased. The electrochemical performance of the samples showed that the discharge capacity decreased as the size of the sample increased, which may result from the high surface area and small size. The magnetic hysteresis measurements taken at 5 K showed that the coercivities of the samples were related to the aspect ratios of the samples, which may result from the larger shape anisotropy. However, the temperature-dependent field cooling magnetization showed that there was no Morin transition in the as-prepared samples, which may result from the surface effect.The products are composed of a large number of nanorods. These rods, about 30 nm in diameter and up to 400 nm long, have smooth surfaces along their entire length.
Keywords: Hematite; Hydrothermal; Size-dependent; Optical absorption; Lithium ion battery; Magnetism
A finite element model of loading and unloading of an asperity contact with adhesion and plasticity
by Yan Du; Lei Chen; Nicol E. McGruer; George G. Adams; Izhak Etsion (pp. 522-528).
An elastic–plastic microcontact with adhesion was studied using a finite element model. This model differs from the existing models, in that it includes the effect of adhesion on the deformation and stresses field, making it applicable to a wide range of material properties. It shows two distinct separation modes, brittle separation and ductile separation. To the best of our knowledge this is the first time that a finite element model has predicted ductile separation in an adhesive contact. Three key parameters affecting the contact and separation modes are also discussed. Further work is expected to fully reveal the effect of these parameters on the separation modes.An elastic–plastic microcontact with adhesion was studied using the finite element model. The formation of a neck during the separation of Au represents a ductile separation.
Keywords: Adhesion; Lennard-Jones potential; Elastic–plastic contact; Load–unload; Ductile separation; Brittle separation