Journal of Colloid And Interface Science (v.313, #2)
Editorial Board (OFC).
Preparation of monodisperse thermo-sensitive poly(N-isopropylacrylamide) hollow microcapsules by Chang-Jing Cheng; Liang-Yin Chu; Ping-Wei Ren; Jie Zhang; Lin Hu (383-388).
We successfully developed a novel and simple method for preparation of monodisperse thermo-sensitive poly(N-isopropylacrylamide) (PNIPAM) hollow microcapsules at the interface of water-in-oil (W/O) single emulsions at a temperature below the lower critical solution temperature (LCST) of PNIPAM. The prepared PNIPAM microcapsules are featured with hollow structures and thin membranes, high monodispersity, excellent reversible thermo-sensitivity and fast response to environmental temperature. This approach exhibits great interests in preparing monodisperse thermo-sensitive microcapsules for encapsulating bioactive materials or drugs requiring mild encapsulation conditions, because of the flexibility in choosing substances being dissolved in the aqueous phase. The preparation methodology demonstrated in this study provides a unique approach for preparing monodisperse hollow polymeric microcapsules with W/O single emulsions.A novel and simple method has been developed for preparation of monodisperse thermo-sensitive poly(N-isopropylacrylamide) hollow microcapsules at the interface of water-in-oil single emulsions at a temperature below the lower critical solution temperature of PNIPAM. The prepared microcapsules are featured with hollow structures and thin membranes, high monodispersity, excellent reversible thermo-sensitivity and fast response to environmental temperature.
Keywords: Hollow microcapsules; SPG membrane emulsification; N-isopropylacrylamide; Photopolymerization; Stimuli-sensitive polymers;
Competitive adsorption of sodium dodecyl sulfate and polyethylene oxide at the air/water interface by Nicolas Péron; Róbert Mészáros; Imre Varga; Tibor Gilányi (389-397).
The interfacial and bulk behavior of the aqueous solutions of sodium dodecyl sulfate (SDS) and polyethylene oxide (PEO) was investigated by surface tension measurements in the presence of excess NaBr. The Gibbs analysis demonstrated that the surfactant nearly completely displaces the polymer from the surface even below the cac. Furthermore, the adsorbed amount of SDS revealed universal features in the presence of PEO above M PEO = 8 × 10 3 , i.e. it was found to be independent of the polymer molar mass. The results were also compared with previous neutron reflection measurements on PEO/SDS system without added salt. This comparison revealed that the extent of surfactant adsorption as well as the displacement of the polymer is more pronounced at high ionic strength. This finding might be attributable to the increased adsorption driving force of SDS in 0.1 M NaBr. Above the cac the criteria of the precise determination of surfactant binding isotherms from surface tension measurements were investigated. It was shown that the usual formula used for the calculation of the bound amount of surfactant from surface tension can only be used at high ionic strength. Finally, it was suggested that a sufficient test for the plausibility of the calculated binding isotherms might be their independence on the polymer concentration in the whole surfactant concentration range and not only at the cmc as the earlier studies claimed.The polymer desorption due to competition with surfactant was almost complete below the critical aggregation concentration. This property can be used to calculate the binding of the surfactant on polymer.
Keywords: Solutions of polymers and surfactants; Polymer/surfactant interaction; Adsorption; Surface tension; Binding isotherm;
Electro-optics of colloid–polyelectrolyte complexes: Counterion condensation on free and adsorbed sodium carboxymethyl cellulose by Kamelia Kamburova; Tsetska Radeva (398-404).
Electrical properties of sodium carboxymethyl cellulose (NaCMC) in aqueous solution and after addition to a dilute suspension of β-ferric hydrous oxide particles (β-FeOOH) are studied by means of electric birefringence method. We established extended conformation of the NaCMC chains in a solution at concentration 10 −2 g dm−3, which is found high enough to assure overcharging of the particle surface. The frequency behavior of the electric birefringence of NaCMC solution with concentration 10 −2 g dm −3 is found similar to the behavior of the suspension of β-FeOOH particles containing same amount of polyelectrolyte. The observed decrease in the relaxation frequency of the electro-optical effect in both systems is attributed to polarization of condensed counterions near to the polyion surface. These results are in line with our previous estimation, showing that the condensed counterions are not released from NaCMC because of its adsorption onto weakly charged particle surface. They also reveal that, at overcompensation of the particle charge, the electrical properties of the adsorbed polyion dominate the electro-optical behavior of the weakly charged particle.Participation of condensed counterions in creation of the electro-optical effect from sodium carboxymethylcellulose (NaCMC) in solution and after adsorption on weakly charged oxide particles was investigated by means of electric birefringence.
Keywords: Colloid–polyelectrolyte complexes; Counterion release from adsorbed polyelectrolyte; Polyelectrolyte adsorption; Overcharging of colloids; Electro-optics of colloid–polyelectrolyte complexes;
Sorption of nonionic organic solutes from water to tetraalkylammonium bentonites: Mechanistic considerations and application of the Polanyi–Manes potential theory by Megan Fuller; James A. Smith; Susan E. Burns (405-413).
This work describes the role of quaternary alkylammonium amendment length on sorption mechanisms of modified bentonites for four nonionic organic compounds; benzene, carbon tetrachloride, TCE, and 1,2-DCB. Tetramethyl to tetrabutyl alkyl amendments were studied and an important mechanistic shift occurred at the propyl chain length for all four solutes studied. Three- and four-carbon-chain functional groups on the ammonium cation resulted in a linear, rather than a curvilinear isotherm. The uptake on tetrapropyl and tetrabutylammonium clays was noncompetitive in binary systems and showed negligible sensitivity to temperature variations, indicating the linear isotherms describe a partitioning uptake mechanism for these organoclays. The adsorptive organoclays (tetramethyl and tetraethylammonium clays) were fit with the Dubinin–Radushkevich equation to investigate the application of the Polanyi–Manes potential theory to organoclay adsorption. It was found that TCE and carbon tetrachloride, with similar physical and chemical characteristics, behaved according to the Polanyi–Manes theory. Benzene showed an anomalously high adsorption volume limit, possibly due to dense packing in the adsorption space or chemisorption to the short chain alkyl groups.An experimental study was performed to evaluate the adsorption/partition transition in nonionic solute uptake to tetraalkylammonium bentonites. The adsorptive equilibrium isotherms were fit with the Dubinin–Radushkevich model derived from the Polanyi–Manes potential theory.
Keywords: Organoclay; Quaternary ammonium cation; Dubinin–Radushkevich equation; Polanyi–Manes adsorption potential; Adsorption; Partition;
Computer simulation of adsorption kinetics of surfactants on solid surfaces by Xianren Zhang; Biaohua Chen; Zihao Wang (414-422).
Adsorption kinetics of surfactants on solid surfaces has been studied by using computer simulation. Both bulk surfactant concentration and diffusion region are explicitly integrated in our model. Depending on the head–surface interaction, our simulation results indicate that there exist two different kinetic modes in adsorption process of surfactants on solid surfaces. One is the four-regime mode and the other is step-wise mode. For the strongly attractive head–surface interaction, four distinct regimes of surfactant adsorption are found: a diffusion-controlled regime, a self-assembly controlled regime, an intermediate coverage regime and a saturated regime. In particular, the adsorption in second regime displays a power-law time dependence with an exponent unrelated to bulk concentrations and diffusion coefficients. While for the weaker adsorption surfaces, the step-wise mode is found. The mode includes a low-coverage nucleation regime and the saturated regime after a sudden aggregation of surfactants on the substrates which occurs stochastically. Besides the head–surface interaction, in this work, the effects of surfactant diffusivity, bulk concentration, the length of diffusion zone and surfactant architecture on the adsorption kinetics are also considered. The simulated adsorption kinetics is compared qualitatively with experimental results.
Keywords: Adsorption kinetics; Surfactant; Computer simulation; Lattice model;
Modeling the sorption kinetics of divalent metal ions onto mineral adsorbent using integral method by Nidhi Singhal; Murari Prasad; Neelmani Gupta; Vineet Kumar (423-427).
A mathematical model has been developed that could predict kinetic parameters for the adsorption of divalent cations (lead, copper and zinc) onto low-grade rock phosphate using experimental data. The experiments were conducted with the initial concentrations of metal ions ranging from 10 to 100 mg/L. The mathematical model is based on application of Freundlich isotherm to mass transfer across the film surrounding the adsorbent. A code in C programming is used to numerically integrate the model equation, and to obtain the best simulated values of Freundlich constants K, N, order of reaction n, and film transfer coefficient, α. It is observed that the adsorption of metal ions on rock phosphate is more sensitive to N , n , and α in comparison to K, and lead is adsorbed more favorably than copper and zinc.Divalent metal sorption system is modeled using numerical integration method. The proposed model fits experimental data satisfactorily and favorable adsorption occurs for lead and zinc onto rock phosphate.
Keywords: Adsorption; Divalent metal ions; Low-grade rock phosphate; Mathematical model; Trapezoidal method; Gradient descent; Least square analysis; Freundlich constant; Mass transfer; Film transfer constant;
Numerical analysis of nitrogen adsorption isotherms on active carbons by an employment of the new LBET class models by Mirosław Kwiatkowski (428-439).
The reported research concerns properties of the new LBET class models designed to describe the heterogeneous adsorption on microporous carbonaceous materials. In particular, the new adsorption models were used for the analysis of the microporous structure of two active carbons on the basis of nitrogen adsorption isotherms. This paper gives more information on the properties of the proposed identification technique.
Keywords: Adsorption; Heterogeneous; Microporous; Isotherms; Computer calculations;
Role of background ions in guar gum adsorption on oxide minerals and kaolinite by Xiaodong Ma; Marek Pawlik (440-448).
Adsorption of guar gum onto alumina, titania (rutile), hematite, quartz, and kaolinite was investigated as a function of pH, ionic strength (from distilled water to saturated NaCl and KCl), and the type of background electrolyte (0.01 mol/L LiCl, NaCl, KCl, and CsCl). It was demonstrated that the adsorption density of the polymer does not depend on pH for any of the tested minerals, so only hydrogen bonding was identified as the dominant adsorption mechanism. The minerals could, however, be divided into two groups depending on the effect of the salt type on polymer adsorption. Guar gum adsorption onto quartz and kaolinite significantly increased in the presence of even a small amount of KCl, while NaCl equally enhanced guar gum adsorption on these two minerals only at concentrations approaching saturation. In contrast, no significant differences between the effects of KCl and NaCl on polysaccharide adsorption were observed on titania, alumina, and hematite. The results were correlated with the chaotropic (KCl) and kosmotropic (NaCl) properties of the background salts, and—based on a review of the available literature data—with the presence (quartz) or absence (titania, alumina, hematite) of an extensive hydration layer on the oxide surfaces. It was concluded that the main role of background ions in the studied systems was to control the stability of the interfacial water layer on oxide particles whose presence serves as a barrier to guar gum adsorption.
Keywords: Guar gum; Oxide minerals; Polymer adsorption; Ionic strength;
Effective diffusion coefficient determination within cylindrical granules of adsorbents using a direct simulation method by Zimei Rong; Artur P. Terzyk; Piotr A. Gauden; Pankaj Vadgama (449-453).
Analytical expressions for solute adsorption kinetics within porous carbon cylindrical granules of adsorbents with a one point formula for effective diffusion coefficient determination are available based on the assumption that solute transport is the rate limiting step and that it follows Fick's Second Law. Here the first practical application of this theory is provided with an initial, estimated diffusion coefficient refined by fitting calculated kinetic adsorption curves to experimental data determined for activated carbons. In an ideal experiment, experimental error (noise) is negligible, and no data refinement is needed. However, real experimental data are always more or less noise contaminated. Where such noise is significant, a simulation method offers the best value for effective diffusion coefficient. For this specific system, surface modification, pH and temperature effects on adsorption kinetics were analysed quantitatively as a basis of determining effective diffusion coefficients through the porous structure.An apparent solute diffusion coefficient in cylindrical carbon granules is estimated with a middle point formula and refined by fitting a simulated adsorption curve to the experimental data.
Keywords: Kinetics of adsorption; Adsorption from solution; Bipartite expression; Simulation; Diffusion coefficient; Cylinder;
Contact angle measurements by confocal microscopy for non-destructive microscale surface characterization by Mark Sundberg; Alf Månsson; Sven Tågerud (454-460).
Contact angle measurements are of great importance in surface characterization but the practical use has often been limited to macroscopic dimensions (millimeters). Therefore, we have developed a confocal microscopy method that allows non-destructive measurements of both low (<30°) and high (30°–90°) contact angles. Low contact angles were measured by reconstructing the drop profile from the interference patterns in droplets condensed from atmospheric humidity. At higher contact angles water droplets with a small amount of fluorescein were sprayed onto the surfaces and 3D-image stacks were recorded and used to extract the contact angle. Suitable drop sizes were between a few up to about 50 μm radius, using a 40× magnification objective. Using drops >10 micrometers radius for microcontact angle measurements a good correlation was obtained between measured micro- and macrocontact angles. After microcontact angle measurements the surfaces were rinsed and heavy meromyosin motor fragments were adsorbed to the surface. Importantly, the sensitive actin propelling function of these motor proteins was not affected by the previous contact angle measurements using fluorescent droplets. This suggests that the methodology should be suitable for non-destructive characterization of different parts of micropatterned surfaces being developed for biological assays.A retouched 3D-representation of a confocal microscopy image stack of water droplets with a fluorescent probe (scales in micrometers). The contact angle was derived from the reconstructed drop profile.
Keywords: Line tension; Confocal microscopy; Interference; Contact angles; Surface characterization; Fluorescein; Modified Young's equation; Myosin; Actin; Motility assay;
Structure of water in the vicinity of amphoteric polymers as revealed by Raman spectroscopy by Hiromi Kitano; Kyoko Nagaoka; Susumu Tada; Makoto Gemmei-Ide (461-468).
The structure and hydrogen bonding of water in an aqueous solution of amphoteric copolymers (poly(MA-r-DMAPMA), 3 × 10 3 < M w < 10 4 ) composed of various ratios of methacrylic acid (MA) and N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA) were analyzed using the band shapes of the O―H stretching in the polarized Raman spectra. The number of hydrogen bonds disrupted due to the presence of one monomer residue ( N corr value) evaluated for poly(methacrylic acid) was largely positive, and with an increase in the content of the DMAPMA residue, the N corr value became smaller, and after passing a minimum (which was still slightly positive) at a roughly equivalent molar ratio (P(M47D53); M, methacrylic acid; D, N-[3-(dimethylamino)propyl]methacrylamide), increased again. This is in a significant contrast with the largely positive N corr values for the homopolymers of MA and DMAPMA, and other ordinary polyelectrolytes. The small N corr value for P(M47D53) was comparable to those for water-soluble nonionic polymers such as poly(ethylene glycol) and zwitterionic polymers such as polycarboxybetaine. These results suggested that the balance of electric charges in polymeric materials is important to be inert to the structure of vicinal water.
Keywords: Amphoteric polymer; Hydrogen-bonded network; O―H stretching; Raman spectroscopy; Water structure;
Probe diffusion from dilute to concentrated in polyelectrolyte solution: Salt effect by Young-Wook Choi; Seoungyeol Lee; Kyungbae Kim; Paul S. Russo; Daewon Sohn (469-475).
The adsorption behaviors between a positively charged poly(allyamine) hydrochloride (PAH) matrix and negatively charged sulfate polystyrene (PS) particle probe were investigated using dynamic light scattering (DLS) and fluorescence photobleaching recovery (FPR) with reference to the matrix and salt concentration. The system experienced a steep decrease of diffusion (flocculation) under dilute conditions and a gradual decrease above semidilute concentrations. The fluorescence photobleaching recovery and viscometry experiments revealed that the probe behaviors in the polyelectrolyte solution were strongly affected by the coil overlap concentration (0.5 g/L poly(allyamine) hydrochloride). Near the coil overlap concentration, the hydrodynamic radius representing the entanglement dimension of the matrix was approximately 30 nm; however, at higher concentrations the radius gradually decreased, suggesting a transition toward a network structure. In this system, the salt performed two roles: (1) reinforcing the electrostatic interaction, and (2) preventing electrostatic interaction between the probe and the matrix.The adsorption behaviors between a positively charged poly(allylamine) hydrochloride (PAH) matrix and negatively charged sulfate polystyrene (PS) particle probe were investigated using dynamic light scattering (DLS) and fluorescence photobleaching recovery (FPR) with references to the matrix and salt concentration.
Keywords: Light scattering; FPR; Salt effect; S–E deviation; Overlap coil concentration; Flocculation;
Interfacial behavior between atmospheric-plasma-fluorinated carbon fibers and poly(vinylidene fluoride) by Kingsley K.C. Ho; Steven Lamoriniere; Gerhard Kalinka; Eckhard Schulz; Alexander Bismarck (476-484).
Atmospheric-plasma fluorination was used to introduce fluorine functionalities onto the surface of carbon fibers without affecting their bulk properties. The interfacial adhesion between atmospheric-plasma-fluorinated carbon fibers and poly(vinylidene fluoride) (PVDF) was studied by means of direct wetting measurements and single fiber pullout tests. Measured contact angles of PVDF melt droplets on modified carbon fibers show that short exposure times of carbon fibers to atmospheric-plasma fluorination (corresponding to a degree of surface fluorination of F/C = 0.01 (1.1%)) leads to improved wettability of the fibers by PVDF melts. The apparent interfacial shear strength as a measure of practical adhesion, determined by the single-fiber pullout test, increases by 65% under optimal treatment conditions. The improved practical adhesion is not due to the formation of transcrystalline regions around the fibers or a change of the bulk matrix crystallinity or to an increased surface roughness; it seems to be due to the compatibilization of the interface caused of the atmospheric-plasma fluorination of the carbon fibers.The impact of atmospheric-plasma fluorination of carbon fibers on the interaction between carbon fibers and poly(vinylidene fluoride) was studied by means of melt contact angle and interfacial shear strength measurements. Results show an improvement of 65% in the practical adhesion after only 1 min treatment.
Keywords: Carbon fibers; Fluorination; Contact angle; Interface; Adhesion; Surface area; Fiber properties;
Complex formation in mixtures of lysozyme-stabilized emulsions and human saliva by Erika Silletti; Monique H. Vingerhoeds; Willem Norde; George A. van Aken (485-493).
In this paper, we studied the interaction between human unstimulated saliva and lysozyme-stabilized oil-in-water emulsions (10 wt/wt% oil phase, 10 mM NaCl, pH 6.7), to reveal the driving force for flocculation of these emulsions. Confocal scanning laser microscopy (CSLM) showed formation of complexes between salivary proteins and lysozyme adsorbed at the oil–water interface and lysozyme in solution as well. To assess the electrostatic nature of the interaction in emulsion/saliva mixtures, laser-diffraction and rheological measurements were conducted in function of the ionic strength by adding NaCl to the mixture in the range between 0 and 168 mM. Increasing the ionic strength reduced the ability of saliva to induce emulsion flocculation as shown by the decreased floc size and the effect on the viscosity. Turbidity experiments with varying pH (3–7) and ionic strength also showed decreased complex formation in mixtures between saliva and lysozyme in solution upon NaCl addition up to 200 mM. Decreasing the pH increased the turbidity, in line with the increase of the positive net charge on the lysozyme molecule. We conclude that electrostatic attraction is the main driving force for complex formation between saliva components and lysozyme adsorbed at the oil droplets and in solution.CLSM of complex formation between lysozyme-stabilized emulsion (on the left) and lysozyme in solution (on the right) after mixing with saliva.
Keywords: Lysozyme; Emulsion; Saliva; Interaction; Complex formation;
Size-controlled gold nanocolloids on polymer microsphere-stabilizer via interaction between functional groups and gold nanocolloids by Wei Liu; Xinlin Yang; Lei Xie (494-502).
Gold nanocolloids with the controlled diameter ranging from 5.2 to 10.7 nm were in situ prepared by reduction of gold chloride trihydrate with sodium borohydride as reductant via the interaction between the gold naocolloids and the functional groups on the surface of polymer microsphere-stabilizer. The nature of such interaction was studied in detail by X-ray photoelectron spectroscopy (XPS). The effect of the functional groups on the catalytic activity of the gold nanocolloids was preliminarily investigated with the reduction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride as reductant.Gold nanocolloids with the controlled diameter ranging from 5.2 to 10.7 nm were in situ prepared by reduction of gold chloride trihydrate with sodium borohydride as reductant via the interaction between the gold atoms and the functional groups on the surface of polymer microsphere-stabilizer.
Keywords: Size-controlled; Gold nanocolloids; Interaction; Catalyst;
Synthesis of PVP-stabilized ruthenium colloids with low boiling point alcohols by Yuqing Zhang; Jiulong Yu; Haijun Niu; Hanfan Liu (503-510).
A route to the preparation of poly(N-vinyl-2-pyrrolidone) (PVP)-stabilized ruthenium colloids by refluxing ruthenium(III) chloride in low boiling point alcohols was developed. Deep purple colloids with shuttle-like ruthenium particles were also synthesized. XPS measurement verified the nanoparticles were in the metallic state. The morphology of metal nanoparticles was characterized by UV–visible absorption spectrophotometry, TEM and XRD.Dark brown Ru colloids or deep purple colloids with shuttle-like nanostructures can be prepared by refluxing RuCl3 with PVP in low boiling point alcohols.
Keywords: Polymer-stabilized colloids; Poly(N-vinyl-2-pyrrolidone); Ruthenium; Alcohol reduction;
Continuous production of water dispersible carbon–iron nanocomposites by laser pyrolysis: Application as MRI contrasts by Y. Leconte; S. Veintemillas-Verdaguer; M.P. Morales; R. Costo; I. Rodríguez; P. Bonville; B. Bouchet-Fabre; N. Herlin-Boime (511-518).
Carbon encapsulated iron/iron-oxide nanoparticles were obtained using laser pyrolysis method. The powders were processed to produce stable and biocompatible colloidal aqueous dispersions. The synthesis method consisted in the laser decomposition of an aerosol of ferrocene solution in toluene. This process generated, in a continuous way and in a single step, a nanocomposite formed by amorphous carbon nanoparticles of 50–100 nm size in which isolated iron based nanoparticles of 3–10 nm size are located. The effect of using different carriers and additives was explored in order to improve the efficiency of the process. The samples after purification by solid–liquid extraction with toluene, were oxidised in concentrated nitric acid solution of sodium chlorate, washed and finally ultrasonically dispersed in 1 mM tri-sodium citrate solutions. The dispersions obtained have hydrodynamic particle size less than 150 nm and are stable in the pH range of 2–11. Finally the shortening of the transversal relaxation time of water protons produced by the dispersed particles was studied in order to test the feasibility of these systems to be traced by magnetic resonance imaging techniques.
Keywords: Magnetic particles; Laser pyrolysis; Nanocomposites; Fe/C;
Adsorption behavior of DODAB/DPPC vesicles on silica by Sérgio P. Moura; Ana M. Carmona-Ribeiro (519-526).
The interaction between composite dipalmitoylphosphatidylcholine (DPPC)/dioctadecyldimethylammonium bromide (DODAB) bilayer vesicles in the gel state and silica is investigated over the 0–20% DODAB range from determination of adsorption curves, silica sedimentation, particle sizing and zeta-potentials. At 1 mg/mL silica, 0% DODAB, pH 6.3, over the 0–150 mM NaCl range of ionic strengths, high affinity adsorption curves were barely affected by ionic strength and all of them exhibited limiting adsorption values above the level expected for single bilayer deposition. At 1 mg/mL silica, 2% DODAB, pH 6.3 and 1 mM NaCl, high affinity adsorption curves fortuitously presented limiting adsorption indicative of one bilayer deposition on each silica particle. At %DODAB < 2% or %DODAB > 2%, limiting adsorption was above and below the level expected for bilayer deposition, respectively. Increasing %DODAB in the vesicle composition negatively modulated the limiting adsorption on silica despite the increasing surface charge on vesicles and electrostatic attraction between vesicles and particles. The results point out the difficulty of closed vesicle disruption (required for bilayer deposition from vesicles) when the bilayer is tightly packed in the rigid gel state and might be of interest for analytical applications of immobilized vesicles on silica.
Keywords: Dipalmitoylphosphatidylcholine; Dioctadecyldimethylammonium bromide vesicles; Aerosil OX-50; Adsorption; Colloid stability;
Agglomeration of alumina submicronparticles by silica nanoparticles: Application to processing spheres by colloidal route by P. Garcia-Perez; C. Pagnoux; A. Pringuet; A. Videcoq; J.F. Baumard (527-536).
In aqueous media, heterocoagulation between submicronic alumina (400 nm) and nanometric silica (25 nm) leads to the adsorption of silica on the alumina surface. By controlling the coverage rate of alumina particles, this adsorption destabilizes the suspension that leads to a very porous network of agglomerated particles. This work shows that the structure is all the more open as the density of charge carried by the two oxides is high and the ionic strength in the suspension low. From such a flocculated suspension, a new colloidal process to fabricate ceramic spheres is proposed which is based on a size increase of agglomerates. Under a controlled rotation of the vessel, electrostatic attraction between the surface charges of opposite polarity induces a size increase of agglomerates until the formation of spheres occurs. It has been shown that the mechanism of growth is poisoned by species adsorbed such as ions. Nevertheless, this new process proves very promising because it leads to a narrow size distribution of spheres by colloidal way, which can be subsequently consolidated by sintering, with a smooth surface.
Keywords: Heterocoagulation; Alumina; Silica; Agglomeration; Sphere; Suspension;
Use of Fe3+ ion probe to study the stability of urea-intercalated kaolinite by electron paramagnetic resonance by Cristiane Regina Budziak Fukamachi; Fernando Wypych; Antonio Salvio Mangrich (537-541).
The effect of mechanical and chemical activation in processes of urea intercalation in the interlayer spacing of kaolinite and the effect of varying the temperature of the intercalation product between 100 and 200 °C were studied using Fe3+ ions as a probe in electron paramagnetic resonance (EPR) spectroscopy. Other techniques were also used to characterize the samples. Monitoring the heating of urea-intercalated kaolinite, FTIR, and XRD revealed that the product obtained was stable up to a temperature of 150–160 °C. The EPR data indicated that the intercalation process promoted an approximation and increase of the magnetic interactions among the Fe3+ ions. The DRUV–vis analysis of the product before heating showed an absorption band at 680 nm that was absent in the raw kaolinite. This band was attributed to the transition A 1 6 → T 2 4 ( G 4 ) in the adjacent Fe3+ ions, intensified by magnetic coupling among these ions. We suggest that intercalated urea forms hydrogen bonds between the carbonyl's oxygen and the hydroxyls bound to the Fe3+ ions of the kaolinite structure. This would cause the approximation of the Fe3+ ions, maximizing magnetic couplings and intensifying concentrated centers of Fe3+, as was visible by EPR spectroscopy.
Keywords: Urea-intercalated kaolinite; Electron paramagnetic resonance; Fe3+ EPR probe;
Micellar kinetic effects in gemini micellar solutions: Influence of sphere-to-rod transitions on kinetics by Amalia Rodríguez; María del Mar Graciani; Kai Bitterman; Ana Teresa Carmona; María Luisa Moyá (542-550).
The reactions 4-nitrobenzenesulfonate + Br− and methyl naphthalene-2-sulfonate + Br− were studied in various water–ethylene glycol, EG, [C12H25(CH3)2N―(CH2) s N(CH3)2C12H25]Br2 micellar solutions (12-s-12,2Br− with s = 3 – 5 methylene groups). Results showed that the observed rate constant of the two reactions varied when a sphere-to-rod transition occurs. This morphological transition is accompanied by changes in the interfacial region water content and in its polarity. The micellar ionization degree is also altered, making the counterion interfacial concentration change. Finally, variations on the molar surfactant volume, V m , also follow the sphere-to-rod transitions. A simple pseudophase kinetic model is inadequate for quantitatively discussing the kinetic micellar effects observed, since the changes accompanying micellar growth affect the second-order rate constant in the micellar pseudophase, the equilibrium binding constant and the surfactant molar volume, neither of them remaining constant in the whole surfactant concentration range. However, this simple model can be helpful in the treatment of kinetic data for surfactant concentrations below the morphological transitions, providing some interesting, although approximate, information.
Keywords: Gemini; Micelles; Kinetics; Sphere-to-rod transitions; Water–ethylene glycol;
Preparation, characterization, and Zn2+ adsorption behavior of chemically modified MCM-41 with 5-mercapto-1-methyltetrazole by Damián Pérez-Quintanilla; Alfredo Sánchez; Isabel del Hierro; Mariano Fajardo; Isabel Sierra (551-562).
A mesoporous silica (MCM-41) has been chemically modified with 5-mercapto-1-methyltetrazole using the homogeneous route. This synthetic route involved the reaction of 5-mercapto-1-methyltetrazole with 3-chloropropyltriethoxysilane prior to immobilization on the support. The resulting material (MTTZ-MCM-41) has been characterized by powder X-ray diffraction, nitrogen gas sorption, FT-IR and MAS NMR spectroscopy, thermogravimetry, and elemental analysis. The solid was employed as a Zn(II) adsorbent from aqueous solutions at room temperature. The effect of several variables (stirring time, pH, metal concentration, addition of ethanol, presence of other metals in the medium) has been studied using batch and column techniques. Flame atomic absorption spectrometry was used to determine the Zn(II) concentration in the filtrate or in the eluted solution after the adsorption process. Results obtained indicate that under the optimum conditions (pH 8 and 2 h stirring time), the maximum adsorption value for Zn(II) was 1.59 ± 0.01 mmol / g , whereas the adsorption capacity of the unmodified mesoporous silica was about 0.010 ± 0.001 mmol / g . On the other hand, the Zn(II) adsorption on the MTTZ-MCM-41 was independent of the presence of ethanol and other metals (Cu(II), Mn(II), Ca(II), and Mg(II)) in the medium. Finally, experiments carried out in order to study the regeneration capacity of the MTTZ-MCM-41 revealed that the adsorption capacity of this material was maintained after 3 cycles of the adsorption/desorption process.Removal of toxic heavy metals from water is a research objective of environmental pollution control processes. 5-Mercapto-1-methyl-1-H-tetrazol ligand is a suitable reagent to obtain functionalized mesoporous silicas with Zn(II) adsorption capacity.
Keywords: 5-Mercapto-1-methyltetrazole; MCM-41; Zinc adsorption; Preconcentration; Characterization of chemically modified MCM-41;
Thermal effects during adsorption of n-butane on a silicalite-1 membrane: A non-equilibrium molecular dynamics study by I. Inzoli; J.M. Simon; S. Kjelstrup; D. Bedeaux (563-573).
Non-equilibrium molecular dynamic (NEMD) simulations have been used to study the kinetics of adsorption of n-butane molecules in a silicalite membrane. We have chosen this simple well-known process to demonstrate that the process is characterized by two stages, both non-isothermal. In the first stage the large chemical driving force leads to a rapid uptake of n-butane in all the membrane and a simultaneous increase in the membrane temperature, explained by the large enthalpy of adsorption, Δ H = − 61.6 kJ / mol butane. A diffusion coefficient for transport across the external surface layer is calculated from the relaxation time; a value of 3.4 × 10 −9 m 2 / s is found. During the adsorption, a significant thermal driving force develops across the external surface of the membrane, which leads to an energy flux out of the membrane during the second stage. In this stage a thermal conductivity of 3.4 × 10 −4 W / K m is calculated from the corresponding relaxation time for the surface, confirming that the thermal conduction is the rate-limiting step. The aim of this paper is to demonstrate that a thermal driving force must be taken into account in addition to a chemical driving force in the description of transport in nano-porous materials.
Keywords: Non-equilibrium molecular dynamics simulation; NEMD; Gas phase adsorption; Thermal effects; Zeolite adsorption;
Chromium removal from water using LTA zeolites: Effect of pH by Elena I. Basaldella; Patricia G. Vázquez; Fabio Iucolano; Domenico Caputo (574-578).
The effect of pH changes on the ability of the synthetic zeolite NaA to remove Cr3+ from water by ion exchange was investigated. The exchange rate was improved by working near neutrality. Despite of the occurrence of simultaneous adsorption, precipitation or cation exchange phenomena, spectroscopic analyses of samples taken at different contact times suggested the presence of an unique chromium environment in the solid phase. The increase in pH observed during the ion exchange favored polymerization–precipitation of chromium species present in solution, which, in turn, improved the metal removal capacity of zeolite NaA above the values expected for a pure cationic exchange reaction.The effect of pH changes on Cr3+ remotion by NaA zeolite is hereby reported. ZeoNa + Cr[H2O]3+ 6 → Na+ + ZeoCr[H2O]3+ 6, ZeoNa + H+ → Na+ + ZeoH+.
Keywords: Chromium removal; Zeolite A; Ion exchange; Heavy metal retention;
Theory of slope-dependent disjoining pressure with application to Lennard–Jones liquid films by Taeil Yi; Harris Wong (579-591).
A liquid film of thickness h < 100 nm is subject to additional intermolecular forces, which are collectively called disjoining pressure Π. Since Π dominates at small film thicknesses, it determines the stability and wettability of thin films. Current theory derived for uniform films gives Π = Π ( h ) . This solution has been applied recently to non-uniform films and becomes unbounded near a contact line as h → 0 . Consequently, many different effects have been considered to eliminate or circumvent this singularity. We present a mean-field theory of Π that depends on the slope h x as well as the height h of the film. When this theory is implemented for Lennard–Jones liquid films, the new Π = Π ( h , h x ) is bounded near a contact line as h → 0 . Thus, the singularity in Π ( h ) is artificial because it results from extending a theory beyond its range of validity. We also show that the new Π can capture all three regimes of drop behavior (complete wetting, partial wetting, and pseudo-partial wetting) without altering the signs of the long and short-range interactions. We find that a drop with a precursor film is linearly stable.Computed drop profiles for different pressure difference C. The critical value C 1 gives a uniform film, whereas C 2 yields a drop with an unbounded precursor film.
Keywords: Disjoining pressure; Thin liquid films; Lennard–Jones potential; Precursor film; Wetting; Contact line;
Adsorption of paraffin vapor on oxidized molybdenum substrates at nano- and micro-scales by Fabrizio Barberis; Dario T. Beruto (592-599).
Sputtered oxidized molybdenum surfaces were exposed at room temperature for different times to paraffin vapors obtained at 150 °C. Scanning polarization force microscopy (SPFM), optical and confocal microscopy were used to characterize the surfaces. The condensed morphologies are complex and strongly dependent upon the quantity of vapor molecules deposited on the substrate surface. A thin paraffin film is initially formed and quite uniform nano-height drops are nucleated randomly over it within 10–20 s time exposures. Their average contact angle ranged between 1°–2.5°. Further vapor deposition led to a more complex regime where nano-height drops do not show a clear interface with the film, while micro-sized drops do. The tangent approximation method adopted by Salmeron and Xu for the nano-drop regimes was extended to the micro-sized drop regime obtaining an averaged effective contact angle equal to 4°–5°. Both nano-height and micro-sized drops shape and effective contact angles have been discussed taking into account their interactions between the film and the drops.The adsorption of paraffin vapor oil on oxidized molybdenum surface lead to complex morphologies, where nano-film, nano-drops, micro-drops and bulk liquid islands are coexisting. Effective contact angles of nano- and micro-drops have been discussed taking into account interactions between film and drops.
Keywords: Mineral oil; Oxidized molybdenum surface; Thin film; Nano-drops; Micro-drops; SPFM; Newton rings;
Mixed Langmuir monolayers of gramicidin A and fluorinated alcohols by Marcin Broniatowski; Katarzyna Obidowicz; Nuria Vila Romeu; Elżbieta Broniatowska; Patrycja Dynarowicz-Łątka (600-607).
Mixed monolayers of gramicidin A (GA) and three alcohols, differing in the degree of fluorination, namely C18OH, F18OH, and F8H10OH have been investigated by means of: surface manometry ( π – A isotherms) and Brewster angle microscopy (BAM) aiming at finding appropriate molecules for incorporating gramicidin A for a biosensor design. Our results proved that only the semifluorinated alcohol is appropriate material for this purpose since it forms miscible and homogeneous monolayers with GA within the whole concentration range. The experimental results have been supported by the calculations of van der Waals energy profiles using the Insight II program. Both the hydrogenated and perfluorinated alcohols were found to aggregate at higher surface pressures, which exclude their application for gramicidin-based biosensor construction.
Keywords: Gramicidin A; Langmuir monolayers; Mixed films; Fluorinated alcohols;
The stability of ultra-thin perfluoropolyether mixture films on the amorphous nitrogenated carbon surface by R.J. Waltman (608-611).
The thermodynamic stability of boundary lubricant films based upon mixtures of liquid perfluoropolyethers (PFPEs) is reported. Mixtures of A20H-2000 with Zdols 2000, 2500, and 4000 and Zdol-TX 2200 on amorphous carbon nitride films are investigated. An optical surface analyzer is used to image the autophobic dewetting of the mixture PFPE films. The critical dewetting thickness coincides with the monolayer thickness of the adsorbed mixture PFPE films as determined by the changes in the surface energy as a function of lubricant film thickness. The critical dewetting thickness varies linearly with mixture concentration.The critical dewetting thickness coincides with the monolayer thickness of the adsorbed mixture PFPE films as determined by the changes in the surface energy as a function of lubricant film thickness.
Keywords: Perfluoropolyether; Perfluoropolyether mixtures; Autophobic dewetting; Surface energy;
Emulsification in turbulent flow by Nina Vankova; Slavka Tcholakova; Nikolai D. Denkov; Vassil D. Vulchev; Thomas Danner (612-629).
Systematic experimental study of the effects of several factors on the breakage rate constant, k BR , during emulsification in turbulent flow is performed. These factors are the drop size, interfacial tension, viscosity of the oil phase, and rate of energy dissipation in the flow. As starting oil–water premixes we use emulsions containing monodisperse oil drops, which have been generated by the method of membrane emulsification. By passing these premixes through a narrow-gap homogenizer, working in turbulent regime of emulsification, we study the evolution of the number concentration of the drops with given diameter, as a function of the emulsification time. The experimental data are analyzed by a kinetic scheme, which takes into account the generation of drops of a given size (as a result of breakage of larger drops) and their disappearance (as a result of their own breakage process). The experimental results for k BR are compared with theoretical expressions from the literature and their modifications. The results for all systems could be described reasonably well by an explicit expression, which is a product of: (a) the frequency of collisions between drops and turbulent eddies of similar size, and (b) the efficiency of drop breakage, which depends on the energy required for drop deformation. The drop deformation energy contains two contributions, originating from the drop surface extension and from the viscous dissipation inside the breaking drop. In the related subsequent paper, the size distribution of the daughter drops formed in the process of drop breakage is analyzed for the same experimental systems.The kinetics of drop breakage in turbulent flow depends on various factors, which can be accounted for by a simple formula—the plot compares the theoretical prediction (dashed line) with a large set of experimental data for the kinetic constants of drop breakage.
Keywords: Kinetics of drop breakage; Emulsification in turbulent flow;
Dielectric analysis of the APG/n-butanol/cyclohexane/water nonionic microemulsions by K.J. He; K.S. Zhao; J.L. Chai; G.Z. Li (630-637).
The nonionic APG/n-butanol/cyclohexane/water microemulsions with different microstructure, which is induced by the variation of water contents, are investigated by the dielectric spectroscopy. An appropriate dielectric theory, Hanai theory and the corresponding analytical method are applied to obtain the internal properties of the constituent phases of microemulsions, such as the relative permittivity and conductivity of continuous and dispersed phases and the volume fraction of dispersed phase. Using these parameters, the distribution of n-butanol in constituent phases, which is of important in the study field of the microstructure of microemulsion, is obtained quantitatively. It is found that the n-butanol molecules not only distribute in the interfacial APG layer but also in the continuous and dispersed phases. In addition, the percolation threshold is interpreted by using the dynamic percolation model. The structural and dynamic information are obtained, for instance, the critical volume fraction of water when percolation occurs and the characteristic time for the rearrangement of clusters. These parameters are intimately related to the properties of microemulsions, especially the characteristics of the interfacial layer.Dielectric spectra of APG/n-butanol/cyclohexane/water microemulsions with different microstructures are analyzed by using Hanai method. The distribution of alcohol in the constituent phases of microemulsions is obtained from the analytical results.
Keywords: Microemulsion; Alkyl polyglucoside; Dielectric spectroscopy; Dielectric analysis; Interfacial polarization;
Effect of surfactant structure on the residual fluorescence of micelle-based fluorescent probes by Yuri Díaz-Fernández; Simón Rodríguez-Calvo; Aurora Pérez-Gramatges; Piersandro Pallavicini; Stefano Patroni; Carlo Mangano (638-644).
In the present paper we have investigated some photo-physical characteristics of different micellar-based fluorescent probes containing a fluorophore (pyrene) and a quencher unit (dodecyl-dioxo 2,3,2). The fluorescent response of the probe in the presence of Cu(II) ions was studied using different micellar substrates, and it was found that the pH at which the On–Off jump occurs is not influenced by the chemical structure of surfactant. In addition, the experimental residual fluorescence is not proportionally affected by microviscosity or by the size of the micellar aggregates. The signal of the native fluorescence of pyrene was observed even when the quencher's occupancy number was greater than one. Moreover, we observed discrepancies between experimental values and calculated residual fluorescence using Laplace data. These results were interpreted suggesting that the residual fluorescence has two main components, one that seems to be independent on micellar properties, while the other is directly related to location of molecules inside the surfactant aggregates that serve as substrate.
Keywords: Fluorescent probe; Micelle; Nonionic surfactant; Residual fluorescence;
Silica nanoparticle sols by Irena Blute; Robert J. Pugh; John van de Pas; Ian Callaghan (645-655).
Surface characterization and foaming studies were carried out with nine industrially manufactured, colloidal silica dispersions with particles sizes from 5–40 nm. All the silica sols produced transient foams with short decay times and the dynamic foam generation (foamability) was found to vary according to the sol type with the greatest foamability occurring for the hydrophobically modified sol and the deionized hydrophilic sol. However, it was found that improved foamability of all the sols could be achieved by changing the pH to within the region of the pHpzc which corresponds to the region of lowest hydrophilicity. An increase in pH (and build-up of negative charge) enhances the surface hydrophilicity and caused a decrease in foamability. In addition, for selected hydrophilic sols, it was shown that the foamability (a) increased with decrease in particle size (within the 6–40 nm range) and (b) increased with particle concentration (within the range of 1–15 wt%). Overall, it was concluded that the foamability was primary controlled by hydrophobicity (and hence by pH) and also by the particle concentration, the particle size and the degree of agglomeration.Silica nanoparticles can be surface active if adsorbed to an air/liquid interface and therefore considered as the substitute for surfactants as stabilizer of foam system.
Keywords: Colloidal silica; Foamability; Foams; Nanoparticles; Surface charge; Ultrasound; Light scattering; Kinematic viscosity;
Self-assembly, hydration, and structures in N-decanoyl-N-methylglucamide aqueous solutions: Effect of salt addition and temperature by J.A. Molina-Bolívar; J.M. Hierrezuelo; C. Carnero Ruiz (656-664).
The influence of NaCl addition and temperature on the self-assembly, hydration, and structures of N-decanoyl-N-methylglucamide (MEGA-10) in dilute solution has been investigated by using several experimental techniques, including tensiometry, steady-state fluorescence, density, viscosity, and static and dynamic light scattering. Tensiometry and fluorescence probe studies, by using pyrene as a probe, were used to obtain the critical micelle concentration (cmc) upon the electrolyte addition. The mean micellar aggregation numbers ( N agg ) as a function of the salt addition were obtained by both static light scattering and static quenching methods. The N agg values estimated by both methods were found to be in good agreement. It was found that the increase in the micelle size, produced by the addition of NaCl, is due to the increase in the aggregation number and in the amount of water non-specifically associated to the micelle. On the other hand, we have observed that the aggregation number remains invariant in the temperature range studied, whereas the hydrodynamic radius slightly decreases. The effect of electrolyte addition and temperature on the properties of MEGA-10 micelles is much less pronounced than those observed in the traditionally used POE-based surfactants.
Keywords: MEGA-10; Surface activity; Micellization; Structure; Hydration;
The emulsion flocculation stability of protein–carbohydrate diblock copolymers by Tim J. Wooster; Mary Ann Augustin (665-675).
The effect of the steric layer thickness on the flocculation stability of β-lactoglobulin–carbohydrate diblock copolymers was assessed. The diblock copolymers were created by conjugating β-lactoglobulin to maltose or a series of different M n maltodextrins using the Maillard reaction. The thickness and spatial arrangement of the interfacial layers were assessed via latex adsorption and selective enzymatic digestion studies. An increase in the molecular weight of the maltodextrin (900, 1900 and 3800 Da) increased the interfacial thickness (1.1, 2.5 and 7.3 nm, respectively). No detectable change to interfacial thickness was observed upon the attachment of maltose. The increase in the interfacial layer thickness scaled with the hydrodynamic size of the carbohydrate. The β-lactoglobulin–maltodextrin conjugates were found to have a diblock architecture, with the protein anchored at the surface and the carbohydrate protruding into the aqueous continuous phase. The stability of oil-in-water emulsions formed using the conjugates was assessed by exposing them to salt (150 mM NaCl or 0–20 mM CaCl2), heat alone or heat in the presence of 150 mM NaCl. Conjugation of a 900 Da maltodextrin provided sufficient steric stabilization to prevent flocculation in high salt environments. The effect of the (number) density of the steric layer was also assessed by controlling the average number of maltodextrins attached per β-lactoglobulin molecule. The steric layer density at which emulsions became unstable was a function of carbohydrate M n . Emulsions made from the 900 Da maltodextrin conjugate became unstable below a steric layer density of one tail per 7.5 nm2, whilst emulsions made from the 1900 Da maltodextrin were unstable below a steric layer density of one tail per 9.5 nm2. This trend was expected and can be explained by the stronger van der Waals attraction that arises from the closer interdroplet separations that are permissible with the shorter maltodextrins. The excellent flocculation stability of Maillard conjugate emulsions is thought to arise from the combined effects of weak electrostatic repulsion from the screened protein surface charge and steric repulsion from the attached carbohydrate layer. This means that attachment of a relatively thin steric layer is enough to stabilize the emulsions against flocculation. These findings have important implications for the development of commercial processes to manufacture protein–carbohydrate Maillard conjugate emulsifiers. Furthermore the work provides a greater empirical understanding of the relationship between interfacial architecture and colloidal stability, and may provide the means for greater theoretical understanding of biopolymer stabilization of interfaces.The difference in β-lactoglobulin–maltodextrin layer digestibility, when exposed to α-amylase or trypsin, highlights their diblock architecture. The thickness of the carbohydrate block controlled emulsion flocculation stability.
Keywords: β-Lactoglobulin; Maillard conjugate; Glycation; Steric stability; Emulsion stability;
Electrophoresis of soft particles at high electrolyte concentrations: An interpretation by the Henry theory by Stanislav S. Dukhin; Ralf Zimmermann; Carsten Werner (676-679).
The existence of electrophoretic mobility at high electrolyte concentrations defines a remarkable peculiarity in the electrosurface characteristics of soft particles. According to Ohshima [H. Ohshima, Colloids Surf. 103 (1995) 249], this effect is caused by the electroosmotic flow within the soft particle shell. An explanation supporting Ohshima's conclusion can be derived from classic electrokinetic theories. Based on the Henry theory [D.C. Henry, Proc. R. Soc. London Ser. A 133 (1931) 106], we demonstrate that the electrophoretic mobility of soft particles does not disappear at decinormal concentration.The Henry theory was applied to demonstrate that the electrophoretic mobility of soft particles does not disappear at decinormal concentration.
Keywords: Electrophoretic mobility; Soft particles;
Viscoelastic behavior of surfactants worm-like micellar solution in the presence of alkanolamide by Dharmesh Varade; Suraj Chandra Sharma; Kenji Aramaki (680-685).
A study of the phase and rheological behavior of anionic surfactant sodium dodecyl trioxyethylene sulfate (SDES) and nonionic polyoxyethylene sorbitan monooleate (Tween-80) with alkanoyl-N-methylethanolamide (C12, NMEA-12; and C16, NMEA-16) in aqueous system is presented. Upon addition of NMEA to the semi-dilute solution of SDES or Tween-80, induces micellar growth leading to the formation of a gel-like highly viscoelastic solution in the maximum viscosity region. These solutions obey the Maxwell model of a viscoelastic fluid. It was observed from rheological measurements that NMEA-16 is more effective than NMEA-12 to induce the micellar growth of surfactants. The relationship between the marked changes in viscosity with surfactant-cosurfactant mixing ratio based on the experimental observations is discussed.
Keywords: Rheology; Phase behavior; Worm-like micelles; Viscoelasticity; Alkanolamide;
Diffusioosmosis of electrolyte solutions in a capillary slit with adsorbed polyelectrolyte layers by Hsien Chen Ma; Huan J. Keh (686-696).
A theoretical study is presented for the steady diffusioosmotic flow of an electrolyte solution in a fine capillary slit with each of its inside walls coated with a layer of polyelectrolytes generated by an imposed tangential concentration gradient. In this solvent-permeable and ion-penetrable surface charge layer, idealized polyelectrolyte segments are assumed to be distributed at a uniform density. The electric double layer and the surface charge layer may have arbitrary thicknesses relative to the gap width between the slit walls. The Poisson–Boltzmann equation and a modified Navier–Stokes/Brinkman equation are solved numerically to obtain the electrostatic potential, dynamic pressure, tangentially induced electric field, and fluid velocity as functions of the lateral position in the slit in a self-consistent way, with the constraint of no net electric current arising from the cocurrent diffusion, electric migration, and diffusioosmotic convection of the electrolyte ions. The existence of the surface charge layers can lead to a diffusioosmotic flow quite different from that in a capillary with bare walls. The effect of the lateral distribution of the induced tangential electric field and the relaxation effect due to ionic convection in the slit on the diffusioosmotic flow are found to be very significant in practical situations.The diffusioosmosis of an electrolyte solution in a capillary slit with adsorbed surface charge layers generated by an imposed tangential concentration gradient is theoretically studied in a self-consistent way.
Keywords: Diffusioosmosis; Polyelectrolyte-coated capillary; Electrokinetic flow; Arbitrary double-layer thickness; Relaxation effect;
Preparation and characterization of N-isopropylacrylamide/acrylic acid copolymer core–shell microgel particles by Aslam Khan (697-704).
A new method has been developed to prepare smart copolymer microgels that consist of well defined temperature sensitive cores and pH sensitive shells. The microgels were obtained from N-isopropylacrylamide (NIPAAm) and acrylic acid (AAc), containing different mole ratios of AAc. Transmission electron micrographs of the microgels show that the colloidal copolymers are nearly monodisperse spheres (core–shell structures). The lower critical solution temperatures (LCSTs) (or phase separation temperatures) of the aqueous microgel solutions were measured by cloud-point method. At slight acidic conditions, the LCST decreased with increase in AAc content, which suggests that the hydrophobic group of NIPAAm has a greater influence on the LCST than the polar ―COOH group at those conditions. An increase of pH value leads to a significant increase in LCST due to the formation of a more hydrophilic copolymer. The LCST were studied as a function of copolymer composition over the pH range from 4.0 to 6.5. Because the p K a of the polymers can be tuned to fall close to neutral pH, these polymer compositions can be dispersed to have phase transitions triggered near physiological pH or at slight acidic pH values that fall within acidic gradients found in biology. Because of their stimuli-responsive behavior, these nanoscale materials are excellent candidates for biotechnology and biomedical applications where small changes in pH or temperature are of great consequence.Colloidal microgels exhibit a reversible temperature dependent hydrophilic/hydrophobic transition at its LCST (lower critical solution temperature) in water.
Keywords: Core–shell; Microgels; Lower critical solution temperature; Temperature sensitive;
Low-temperature growth of ZnO nanorods by chemical bath deposition by Sung-Hak Yi; Seung-Kyu Choi; Jae-Min Jang; Jung-A Kim; Woo-Gwang Jung (705-710).
Aligned ZnO nanorod arrays were synthesized using a chemical bath deposition method at normal atmospheric pressure without any metal catalyst. A simple two-step process was developed for growing ZnO nanorods on a PET substrate at 90–95 °C. The ZnO seed precursor was prepared by a sol–gel reaction. ZnO nanorod arrays were fabricated on ZnO-seed-coated substrate. The ZnO seeds were indispensable for the aligned growth of ZnO nanorods. The ZnO nanorods had a length of 400–500 nm and a diameter of 25–50 nm. HR-TEM and XRD analysis confirmed that the ZnO nanorod is a single crystal with a wurtzite structure and its growth direction is  (the c-axis). Photoluminescence measurements of ZnO nanorods revealed an intense ultraviolet peak at 378.3 nm (3.27 eV) at room temperature.FE-SEM images of aligned ZnO nanorods on PET substrate: (a) ZnO nanorods without seeds (plain view, low magnification); (b) ZnO nanorods with seeds (plain view, low magnification); (c) ZnO nanorods on seeds (cross-section). Nucleation of ZnO nanorod on ZnO seeds has a low free energy barrier of activation than on bare substrate. So, the ZnO seeds were indispensable for the aligned growth of ZnO nanorod.
Keywords: ZnO; Nanorod array; Chemical bath deposition; Sol–gel reaction; Hydrothermal; ZnO seed;
Rodlike silica and titania objects templated on extremely dilute aqueous dispersions of self-assembled sodium lithocholate nanotubes by Xiao Huang; Richard G. Weiss (711-716).
Simple methods for preparation of mesoporous rodlike silica and titania nanoobjects, some with exceedingly high aspect ratios, are described. They involve hydrolytic sol–gel processes using nanotubes from aqueous assemblies of very dilute (0.1 wt%) sodium lithocholate as templates. Shearing of the lithocholate nanotubes results in aligned, templated silica rods. The relative rates of lithocholate self-assembly and of polymerization of the titania precursors, especially, appear to be important factors in templating efficiency.Rodlike silica and titania nanoobjects are templated onto nanotubes of sodium lithocholate in very dilute aqueous media. The templated silica rods are easily aligned by shear.
Keywords: Alignment; Lithocholic acid; Nanorods; Inorganic oxide; Template; Silica; Titania; Self-assembly; BET isotherms;
Synthesis of block copolymer-stabilized Au–Ag alloy nanoparticles and fabrication of poly(methyl methacrylate)/Au–Ag nanocomposite film by Uma Chatterjee; Suresh K. Jewrajka (717-723).
[Poly(2-(N,N-dimethylamino)ethyl methacrylate)]–b–poly(methyl methacrylate)–b–[poly(2-(N,N-dimethylamino)ethyl methacrylate)] ( M n = 45 , 000 ; 20K–5K–20K; PDI = 1.2) block copolymer surfactant stabilized amphiphilic gold–silver alloy nanoparticles (Au–Ag(PDMA–b–PMMA–b–PDMA)) has been synthesized in both water and in organic medium. The block copolymer stabilized pre-made alloy nanoparticles were successfully dispersed in hydrophobic poly(methyl methacrylate) homopolymer matrix (PMMA) of molecular weight 30,000. The successful synthesis of alloy nanoparticles was accessed by Transmission Electron Microscope (TEM), Energy Dispersed X-ray (EDX), and UV–visible spectrophotometric analysis. The surface functionality of the nanoparticles was confirmed by quantitative determining the grafting density of polymer chain around the nanoparticle surface using combination of thermo gravimetric (TGA) and TEM analysis. The hydrodynamic diameter of the alloy particles including the polymer chains was obtained from dynamic light scattering measurement (DLS). The mechanism of synthesis of high concentration of Au–Ag alloy particles from HAuCl4 and AgNO3 (in presence of Cl− from reduction of gold salt) metal particles precursors and the successful preparation of poly(methyl methacrylate)/gold–silver nanocomposite films have been discussed.[Poly(2-(N,N-dimethylamino)ethyl methacrylate)]–b–poly(methyl methacrylate)–b–[poly(2-(N,N-dimethylamino)ethyl methacrylate)] triblock copolymer stabilized Au–Ag nanoparticles are well dispersed in hydrophobic poly(methyl methacrylate) polymer matrix due to compatibility of the nanoparticle surface with the polymer matrix.
Keywords: Amphiphilic gold–silver alloy nanoparticle; Block copolymer; Grafting density; Polymer–metal nanocomposite;
Biomolecule induced nanoparticle aggregation: Effect of particle size on interparticle coupling by Soumen Basu; Sujit Kumar Ghosh; Subrata Kundu; Sudipa Panigrahi; Snigdhamayee Praharaj; Surojit Pande; Subhra Jana; Tarasankar Pal (724-734).
Gold nanoparticles of variable sizes have been prepared by reducing HAuCl4 with trisodium citrate by Frens' method. It has been found that the gold particles under consideration produce well-ordered aggregates upon interaction with a biomolecule, glutathione in variable acidic pH condition and exhibit pronounced changes in their optical properties arising due to electromagnetic interaction in the close-packed assembly. The effect of nanoparticle size on the nature of aggregation as well as the variation in the optical response due to variable degree of interparticle coupling effects amongst the gold particles have been investigated. The optical properties of the gold aggregates have been accounted in the light of Maxwell-Garnett effective medium theory considering the changes in the filling factor in different aggregates produced by variable sizes of gold colloids. The aggregates have been characterized by UV–vis spectroscopy, FTIR, Raman, XRD and TEM studies. It has been observed that a new peak appearing at a longer wavelength intensifies and shifts further to the red from the original peak position depends on the particle size, concentration of glutathione and pH of the solution. On the basis of the first appearance of a clearly defined new peak at longer wavelength, a higher sensitivity of glutathione detection has been achieved with gold nanoparticles of larger dimension.
Keywords: Biomolecule; Surface plasmon; Nanoparticle assembly; Filling factor;
Forces and friction between hydrophilic and hydrophobic surfaces: Influence of oleate species by Katarina Theander; Robert J. Pugh; Mark W. Rutland (735-746).
The atomic force microscope has been used to investigate normal surface forces and lateral friction forces at different concentrations of sodium oleate, a frequently used fatty acid in the deinking process. The measurements have been performed using the colloidal probe technique with bead materials consisting of cellulose and silica. Cellulose was used together with a printing ink alkyd resin and mica, whereas silica was used with a hydrophobized silica wafer. The cellulose–alkyd resin system showed stronger double layer repulsion and the friction was reduced with increasing surfactant concentration. The adhesive interaction disappeared immediately on addition of sodium oleate. The normal surface forces for cellulose–mica indicated no apparent adsorption of the sodium oleate however, the friction coefficient increased on addition of sodium oleate, which we ascribe to some limited adsorption increasing the effective surface roughness. The silica–hydrophobic silica system showed a completely different surface force behavior at the different concentrations. An attractive hydrophobic interaction was evident since the surfaces jumped into adhesive contact at a longer distance than the van der Waals forces would predict. The strong adhesion was reflected in the friction forces as a nonlinear relationship between load and friction and a large friction response at zero applied load. Indirect evidence of adsorption to the hydrophilic silica surface was also observed in this case, and QCM studies were performed to confirm the adsorption of material to both surfaces.Force and friction measurements have been performed using the atomic force microscopy and the colloidal probe technique in liquid environment at different concentrations of sodium oleate.
Keywords: Surface force; Friction; Nanotribology; Deinking; Fatty acid; Sodium oleate; Adsorption; AFM; Colloidal probe; Cellulose;
Al-pillared montmorillonite clay minerals: Low-pressure CO adsorption at room temperature by Atsushi Itadani; Masashi Tanaka; Takahiro Abe; Hideki Taguchi; Mahiko Nagao (747-750).
Three kinds of Al-pillared montmorillonite clay minerals (AlPMON) ion-exchanged with cobalt(II), nickel(II), or copper(II) ions were prepared (abbreviated as CoAlPMON, NiAlPMON, or CuAlPMON, respectively). For the 673-K- and 873-K-treated samples, carbon monoxide (CO) adsorption measurement was performed at room temperature under an atmosphere of low CO pressure. The 873-K-treated CuAlPMON sample exhibited more efficient adsorption properties for CO molecules, in comparison with both-temperatures-treated CoAlPMON and NiAlPMON samples and the 673-K-treated CuAlPMON sample. In addition, irreversibly adsorbed CO was present only on the CuAlPMON sample that had been treated at 873 K; the sites responsible for strong CO adsorption were formed in the sample after the pretreatment at the higher temperature.Irreversibly adsorbed CO molecules at room temperature were present only on the copper-ion-exchanged Al-pillared montmorillonite clay mineral that had been treated at a higher temperature in vacuo among the samples presented in this study; the sites responsible for strong CO adsorption were formed in this clay.
Keywords: Montmorillonite; Al-pillared montmorillonite; Adsorption property; Carbon monoxide; Transition-metal ion;
On the viscoelastic behavior of multiple emulsions by Rajinder Pal (751-756).
The dynamic viscoelastic behavior of multiple emulsions is investigated. A modified Palierne model is used to predict the storage and loss moduli of multiple emulsions. The multiple emulsions exhibit two relaxation domains due to relaxation of two different interfaces—internal and external. The internal interface is the interface between internal droplets and their suspending medium (primary emulsion continuous-phase). The external interface is the interface between multiple-emulsion droplets and their suspending medium (external continuous-phase). The factors affecting the dynamic viscoelastic behavior of multiple emulsions are discussed.The linear viscoelastic behavior of multiple emulsions was investigated. Multiple emulsions exhibit two relaxation domains—one at high frequencies due to relaxation of internal interface and the other at low frequencies due to relaxation of external interface.
Keywords: Emulsion; Multiple emulsion; Double emulsion; Rheology; Viscoelasticity;
Corrigendum to “Electrokinetics integrated” [J. Colloid Interface Sci. 309 (2007) 193] by H. Lyklema (757).
Author Index for Volume 313 (758-759).