Journal of Colloid And Interface Science (v.290, #2)

Effect of SiO2 coating layer morphology on TiH2 gas release characteristic by Zhimao Yang; Jixiang Fang; Bingjun Ding (305-309).
In this study, a uniform and compact SiO2 film-coating layer was prepared on the surface of TiH2 particles by sol–gel method using inexpensive raw materials. The preparation process of SiO2-coated TiH2 particles and the effect of the coating layer morphology on the gas release characteristic were investigated in detail. When the pH value of TiH2 suspending solution is about 4.0 and the concentration of silicic acid is more than 0.5 mol/L, the coating layer shows a SiO2 particle-coating morphology. While a homogeneous and dense film-coating layer can be obtained when the solution pH value and concentration of silicic acid are about 4.0 and 0.5 mol/L. The results of gas release at 700 °C show that TiH2 particles coated with silicon dioxide layers can efficiently delay the starting time of gas release of TiH2 powders to 60–100 s. Comparing the particle-coating layer, the SiO2 film-coating layer has a better delaying effect on gas release of TiH2 particles.
Keywords: Coating; SiO2/TiH2 particle; Gas release characteristic; Al foams;

A new transformation termed the μ-derivative is introduced. Applying it to the Cahn–Hilliard equation yields dynamical exact solutions. It is shown that the μ-transformed Cahn–Hilliard equation can be presented in a separable form. This transformation also yields dynamical exact solutions and separable forms for other nonlinear models such as the modified Korteveg–de Vries and the Burgers equations. The general structure of a nonlinear partial differential equation that becomes separable upon applying the μ-derivative is described.
Keywords: Fluid dynamics; Nonlinear science;

Uranyl sorption onto gibbsite studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) by Nils Baumann; Vinzenz Brendler; Thuro Arnold; Gerhard Geipel; Gert Bernhard (318-324).
Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was combined with batch experiments to study the sorption of uranium(VI) onto gibbsite (γ-Al(OH)3). The experiments were performed under ambient conditions in 0.1 M NaClO4 solution in the pH range from 5.0 to 8.5 using a total uranium concentration of 1 × 10 −5   M , and a solid concentration of 0.5 g/40 ml. Two uranyl surface species with fluorescence lifetimes of 330 ± 115 and 5600 ± 1640   ns , respectively, were identified. The first species was dominating the more acid pH region whereas the second one became gradually more prominent towards higher pH values. The fluorescence spectra of both adsorbed uranyl(VI) surface species were described with six characteristic fluorescence emission bands situated at 479.5 ± 1.1 , 497.4 ± 0.8 , 518.7 ± 1.0 , 541.6 ± 0.7 , 563.9 ± 1.2 , and 585.8 ± 2.1   nm . The surface species with the short-lived fluorescence lifetime of 330 ns is attributed to a bidentate mononuclear inner-sphere surface complex in which the uranyl(VI) is bound to two reactive OH groups at the broken edge linked to one Al. The second surface species with the significant longer fluorescence lifetime of 5600 ns was attributed to small sorbed clusters of polynuclear uranyl(VI) surface species. The longer fluorescence lifetime of the long-lived uranyl surface species at pH 8.5 is explained with the growing average size of the adsorbed polynuclear uranyl surface species.
Keywords: Uranyl; Gibbsite; Adsorption; TRLFS; Emission band; Fluorescence lifetime;

The objective of this work was to investigate whether or not the hydrogen bonding interaction between polymer and crystal surface can be detected by the etching pattern changes in the presence of polymers. The (010) face of acetaminophen single crystal was used as a model solid surface. The etching patterns on the (010) face of acetaminophen crystal by water are in the directions of a- and c-axes, which are the same as the directions of the dominant attachment energies on the (010) face. In the presence of polymer, the hydrogen bonding interactions between adsorbed polymer and crystal surface can affect surface diffusion of acetaminophen molecules and change the etching patterns in the direction of a-axis, i.e., the direction of one hydrogen bond chain. Studies with 2-hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC) and poly(vinyl alcohol) (PVA) showed that polymers, which can form hydrogen bonds with acetaminophen crystal surface, can change etching patterns in the direction of a-axis. Study with Dextran suggested that if a polymer cannot form hydrogen bonds with crystal surface due to steric repulsion, it will not change the etching pattern in the direction of a-axis. Studies with poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) further confirmed that only if a polymer can form hydrogen bonds with acetaminophen on crystal surface, the etching patterns in the direction of a-axis will be affected. The study results suggest that in the presence of polymers, the etching pattern change in the direction of hydrogen bond chain, the a-axis of acetaminophen crystals, can be used to indicate the existence of the hydrogen bonding interactions between adsorbed polymers and acetaminophen crystal surface.
Keywords: Etching pattern; Crystal surface; Polymer; Adsorption; Hydrogen bond;

When small particles are added to a colloidal dispersion of large particles, a depletion interaction between large particles occurs because the small ones are depleted from the gaps between the former particles. In the present paper, a cell model is employed to examine the behavior of a dispersion of large particles immersed in an electrolyte solution containing small particles. In this model, each cell consists of one large particle in its center and an associated atmosphere. Double-layer, van der Waals, and depletion interactions, as well as entropic effects, have been taken into account. When the change of the free energy with respect to that of the electrolyte solution is negative (and this happens in most cases), the dispersions of large particles are stable from a thermodynamic point of view. With increasing volume fraction of the small particles, the free energy change becomes more negative. The formation of gels observed experimentally in concentrated emulsions is explained through the formation of a thermodynamically stable dispersion.
Keywords: Depletion force; Electrostatic interaction; Van der Waals interactions; Thermodynamic stability;

Adsorption of NO on alumina-supported oxides and oxide–hydroxides of manganese by I. Spasova; P. Nikolov; D. Mehandjiev (343-349).
The adsorption capacity for NO of alumina-supported oxides and oxide–hydroxides of manganese have been studied. Two series of samples have been prepared by precipitation on γ-alumina and appropriate thermal treatment. The samples have been characterized by adsorption methods, magnetic methods, electronic paramagnetic resonance (EPR), transient response technique, and temperature-programmed desorption (TPD). The influence of the concentration of the initial manganese-containing solution has been investigated. The sample, prepared with a solution with Mn concentration of 4 g/100 ml, has been shown to be the best adsorbent for NO under the conditions of the experiment. It has been found that the presence mainly of Mn3+ ions on the surface of the support is probably responsible for the enhanced adsorption capacity.
Keywords: Nitrogen oxide; Adsorption; Manganese oxide; Precipitation; Alumina-supported adsorbent; Magnetic methods;

The effect of mineral composition on the sorption of cesium ions on geological formations by József Kónya; Noémi M. Nagy; Zoltán Nemes (350-356).
The sorption of cesium-137 on rock samples, mainly on clay rocks, is determined as a function of the mineral composition of the rocks. A relation between the mineral groups (tectosilicates, phyllosilicates, clay minerals, carbonates) and their cesium sorption properties is shown. A linear model is constructed by which the distribution coefficients of the different minerals can be calculated from the mineral composition and the net distribution coefficient of the rock. On the basis of the distribution coefficients of the minerals the cesium sorption properties of other rocks can be predicted.
Keywords: Bentonites; Cesium-137; Mineral composition; Rocks; Sorption;

Negative adsorption due to electrostatic exclusion of micelles by P. Somasundaran; K.P. Ananthapadmanabhan; Puspendu Deo (357-363).
Interactions of surfactants with solid substrates are important in the controlling of processes such as flotation, coating, flocculation and sedimentation. These interactions usually lead to adsorption on solids, but can also result in an exclusion of the reagents with dire consequences. In this work electrostatic exclusion of negatively charged dodecylbenzene sulfonate micelles from quartz/water, Bio-Sil/water and alumina/water interfaces has been investigated as a function of pH and ionic strength. Measurable negative adsorption of these surfactants from similarly charged solid/liquid interface was observed in the micellar region. In the case of porous samples with large surface area, comparison of pore size with the micelle size is necessary to avoid any erroneous conclusions regarding the role of electrostatic exclusion in a given system. A theoretical model for the electrostatic exclusion of micelles is developed and used to calculate the adsorption of negatively charged dodecylbenzene sulfonate on negatively charged quartz (pH 7), silica (Bio-Sil A, pH 3) and alumina (pH 11) in the micellar concentration region. The micellar exclusion values calculated using the model are in excellent agreement with the experimental results.
Keywords: Electrostatic exclusion; Negative adsorption; Micelles; Zeta potential; Dodecylbenzenesulfonate;

A simple weighted density approximation (SWDA) was extended to nonuniform Lennard–Jones fluids by following the spirit of a partitioned density function theory [S. Zhou, Phys. Rev. E 68 (2003) 061201] and mapping the hard-core part onto an effective hard-sphere fluid whose higher order terms beyond the second order of the functional perturbation expansion are treated by the SWDA. The resultant DFT formalism performs well for Lennard–Jones fluids under the influence of diverse external fields. With the present DFT formalism, we investigate in detail the structure and adsorption properties of a low-density LJ gas in a spherical cavity with a wall consisting of hard-sphere or LJ particles. It was found that when the cavity wall exerts an attractive external potential on the LJ particles in the cavity, the excess adsorption decreases as the temperature increases, while when the cavity wall exerts a hard repulsive external potential on the LJ particles in the cavity, the excess adsorption increases as the temperature increases.

The conformations, the values of the lateral transport coefficient of a charged biomolecule (desmopressin) in the adsorbed layer and in the liquid layers above the adsorbed layer, the potential energies of the interaction between the biomolecules located in different liquid layers with the charged solid surface and with the biomolecules in the adsorbed layer, the potential energies of the interaction between water molecules in the hydration layers surrounding the conformations of the biomolecules in different layers, as well as the structure and number of hydration layers between the different conformations of desmopressin, were determined by molecular dynamics simulation studies. The results show that the lateral mobility of the adsorbed desmopressin is approximately equal to zero and the value of the lateral transport coefficient of the biomolecule in the liquid layers located above the adsorbed layer increases as the distance of the liquid layer from the charged solid surface increases. But the values of the lateral transport coefficient of the biomolecule in the liquid layers above the adsorbed layer are lower in magnitude than the value of the transport coefficient of desmopressin along the direction normal to the charged solid surface in the liquid phase located above the vacant charged sites of the solid surface, and these differences in the values of the transport coefficients have important implications with respect to the replenishment of the biomolecules in the inner parts of a channel (pore), the overall rate of adsorption, and the form of the constitutive equations that would have to be used in macroscopic models to describe the mechanisms of mass transfer and adsorption in the pores of adsorbent media. Furthermore, a novel method is presented in this work that utilizes the information about the sizes of the conformations of the biomolecule in the adsorbed layer and in the liquid layers above the adsorbed layer along the direction that is normal to the charged solid surface, as well as the number and size of the hydration layers along the same direction, and could be used to estimate the value of the lower bound of the linear characteristic dimension of a pore (i.e., pore radius) in porous adsorbent media (e.g., porous adsorbent particles; skeletons of porous monoliths) in order to realize effective transport and overall adsorption rate.
Keywords: Transport and adsorption of biomolecules; Molecular dynamics simulation; Conformation and lateral mobility of biomolecules; Critical pore radius;

Anionic groups (AGs) on different cellulosic fiber surfaces were investigated by methylene blue (MB) and polyelectrolyte (PE) sorption, X-ray photoelectron spectroscopy (XPS), and total attenuated reflectance infrared spectrometry (FTIR-ATR). The MB sorption isotherms fitted well the Langmuir equation that gave consistent estimations of sorption capacities. FTIR-ATR showed that MB molecules had extensive accessibility to the fiber wall pores. Estimation of surface AGs by PE sorption gave much higher values than a new method combining MB sorption and XPS measurements (MB-XPS). The surface AGs in different cellulosic fibers accounted for 1–3% of the total AG content as revealed by MB-XPS. It was suggested that PE molecules can penetrate the fiber wall and form loops or unattached segments at external fiber surfaces that disrupt the PE sorption stoichiometry. The competition of MB and PE for the anionic sites in papermaking was assessed and it was shown that MB ions have a much stronger affinity to AGs than PE molecules.
Keywords: Pulp fibers; Surface chemistry; Carboxyl groups; Papermaking; Paper formulation; Interactions; Langmuir; Freundlich; Equilibrium; Competition;

Interactions of sodium montmorillonite with poly(acrylic acid) by Nguyen H. Tran; Gary R. Dennis; Adriyan S. Milev; G.S. Kamali Kannangara; Michael A. Wilson; Robert N. Lamb (392-396).
The chemical–structural modifications of the natural clay sodium montmorillonite during interaction with poly(acrylic acid) were studied mainly by X-ray photoemission spectroscopy. Samples of modified montmorillonite were prepared from the reaction of sodium montmorillonite (∼0.5 g) and an aqueous solution of poly(acrylic acid) ( pH ∼ 1.8 , 50 g) at varying temperatures. X-ray diffraction indicated that the montmorillonite interlayer space (∼13 Å), formed by regular stacking of the silicate layers (dimension ∼ 1 × 1000   nm ), expanded to ∼16 Å as the reaction was carried out at room temperature and at 30 °C. At 60 °C, the interlayer space further expanded to ∼20 Å. The results of X-ray photoemission spectroscopy indicated that poly(acrylic acid) molecules exchange sodium ions on the surface of the silicate layers. These combined results allowed development of a reaction model that explains the dependency of the interlayer expansion with temperature. Information concerning the surface chemical reactions and systematic increases in the interlayer distances is particularly useful if montmorillonite and poly(acrylic acid) are to be used for formation of nanocomposite materials.
Keywords: Poly(acrylic acid); Clay; Montmorillonite; Interlayer spacing; X-ray photoemission spectroscopy; XRD;

A core–shell copolymer latex with thermal-responsive properties was prepared and its potential application as a vehicle for drug targeting was investigated in this work, where the crosslinked copolymer of N-isopropylacrylamide (NIPAAm) and chitosan was prepared as the core and the copolymer of methacrylic acid (MAA) and methyl methacrylate (MMA) was prepared as the shell. By using soapless dispersion polymerization, the poly(NIPAAm–chitosan) crosslinked copolymer latex was synthesized first. Then the monomers of MAA and MMA were added to continue the reaction to obtain the core–shell copolymer latex. The weight ratio of MAA/MMA and the concentration of shell monomers (MAA and MMA) in the feed of the reaction mixture had been changed to investigate their effects on the particle size, reaction rate, zeta-potential, specific surface area, and surface functional groups of the latex particles. The swelling and thermoresponsive behavior of the film made from these core–shell latices were also studied under different pH values of buffer solution. The model drug (caffeine) could be merged inside the copolymer particles and protected from releasing through the transport process effectively. And the thermoresponsive property of these copolymer particles significantly enhances the ligand (protein) conjugation that shows the potential of the latex being applied on the targeting drug carrier.
Keywords: Poly(chitosan–NIPAAm/MAA–MMA); Core–shell copolymer latex; Shell composition–swelling–drug release relationship; Thermoresponsive;

Control of n-alkanes crystallization by ethylene–vinyl acetate copolymers by Emmanuelle Marie; Yves Chevalier; Franck Eydoux; Laurent Germanaud; Philippe Flores (406-418).
The crystallization of paraffins from their solution at low temperature was investigated in the presence of ethylene–vinyl acetate (EVA) copolymers that allow the control of the size of the crystals. Depending on the type of solvent and distribution of the paraffin lengths, the mechanisms of crystal formation and growth are different. Precipitation of the EVA prior to the paraffins leads to the nucleation of a large number of crystals, whereas the adsorption of EVA on the surface of the growing crystals slows down the crystal growth. EVA can act either as a nucleating agent or as a growth inhibitor. These two mechanisms were identified from the analysis of the temperature of crystallization (cloud point), the chemical composition of the crystals, and the observations of the crystal habit. The EVA was able to co-crystallize with the paraffins in crystals of an orthorhombic structure and the melting enthalpies of the crystalline paraffin did not depend significantly on their neighborhood. The energies of interaction between the different paraffinlike components are close to each other, so that minor changes of the experimental conditions may lead to dramatic effects. This is the basic rationale for the large behavioral diversity observed in these systems.
Keywords: Alkane; Paraffin; Ethylene–vinyl acetate copolymer; Crystallization; Crystal growth; Crystal habit;

Stability of mixtures of charged silica, silica–alumina, and magnetite colloids by J.L. Viota; M. Raşa; S. Sacanna; A.P. Philipse (419-425).
We report experiments on the stability of aqueous mixtures of charged colloidal magnetite and charged silica and silica covered with alumina particles of similar size. First, positively charged magnetite dispersions were mixed with negatively charged silica dispersions at pH 4, at different volume ratios and low colloid volume fractions, producing mixtures which were stable over a period of weeks despite the expected electrostatic attraction between the oppositely charged particles. When magnetite particles were mixed with positively charged silica covered with alumina at pH 4 under exactly the same conditions, some of the systems separated to form a magnetite sediment. When the volume fraction of the initial dispersions was increased, the behavior of the mixtures was the opposite: positive magnetite/negative silica mixtures were unstable at intermediate volume ratios. The unexpected behavior of the mixtures was investigated by means of electrophoretic mobility, initial susceptibility, and dynamic light scattering measurements as well as sedimentation experiments.
Keywords: Colloidal silica particles; Colloidal alumina particles; Magnetic colloids; Magnetic fluids; Heteroaggregation; Stability; Binary mixtures;

Beneficiation of borax by reverse flotation in boron saturated brine by Emin Cafer Çilek; Hasan Üresin (426-430).
Flotation is one of the plausible methods for recovering borax fines discharged as fine waste to the tailings dam in the Kirka borax processing plant. A literature review dealing with the flotation behavior of boron minerals reveals that clay minerals in the boron ores coat boron minerals and thus deteriorate the quality of boron concentrates produced by direct flotation. The main objective of this study is therefore to recover borax fines from the tailings of the concentrator by reverse flotation. A three-level-factor experimental design was used to determine the main and interaction effects of variables selected on the metallurgical performance of reverse flotation. An analysis of variance for experimental results indicates that interaction effects of the variables for concentrate quality and recovery of B2O3 is nonsignificant and the most important variable for grade of concentrate and recovery is the collector dosage. It is shown that a concentrate assaying 11.25% B2O3 with 89.90% B2O3 recovery could be produced by means of single-stage (rougher) reverse flotation. Additionally, in order to produce a sufficient-quality concentrate, a multistage reverse flotation scheme involving rougher, scavenger, and two cleaners was devised. A final concentrate containing 23.47% B2O3 with 81.78% B2O3 recovery was obtained from these tests. The reverse flotation method can be thus considered as an important option for the beneficiation of borax fines.
Keywords: Borax; Reverse flotation; Fine particles; Slime coating; Experimental design;

The effect of calcination temperature on the physico-chemical characterization of manganese nodule leached residue (MNLR) and water-washed manganese nodule leached residue (WMNLR) has been investigated on the basis of chemical analysis, XRD, TG-DTA, FTIR, surface hydroxyl groups, surface oxygen, reducing and oxidizing sites, surface area. XRD and IR confirm the presence of amorphous iron oxyhydroxides, δ-MnO2, which are converted to α-Fe2O3 and γ-Mn2O3 phases above 400 °C of calcination, respectively. A solid solution of Fe2O3 and Mn2O3 is formed above 700 °C. The surface area, surface hydroxyl group, surface oxygen, reducing and oxidizing sites increase with the increase in calcination temperature up to 400 °C and then decrease with further rise in calcination temperature up to 700 °C. The catalytic activity of the sample towards H2O2 decomposition shows the similar trend as surface properties. A suitable Mn3+ ―Mn4+ couple favours H2O2 decomposition reaction. The activity has been correlated with various physico-chemical properties.
Keywords: Manganese nodules leached residue; Surface characterization; Catalytic activity; H2O2 decomposition;

Stability and quantum yield effects of small molecule additives on solutions of semiconductor nanoparticles by Joseph A. Gaunt; Alex E. Knight; Stuart A. Windsor; Victor Chechik (437-443).
The effect of additives on the photostability of semiconductor nanoparticles was studied using CdSe, CdSe/ZnSe and CdSe/ZnS particles of various sizes and composition. The additives included phosphine oxides, amines, and antioxidants. Strong initial enhancement of band edge emission by hexadecylamine was observed for the uncoated particles but stability over a week period in light and air was shown to be poor. Inorganic coatings rendered the nanoparticles initially insensitive to additive but provided little extra stability in terms of photoluminescence. Antioxidant was shown to be effective at reducing the rate of photooxidative degradation for all particles in chloroform but not in toluene.
Keywords: CdSe; CdSe/ZnSe; CdSe/ZnS; Nanoparticles; Photostability; Photooxidation; Amine; Phosphine; Antioxidant;

Silica encapsulation and magnetic properties of FePt nanoparticles by M. Aslam; L. Fu; S. Li; Vinayak P. Dravid (444-449).
Core–shell nanoparticles have emerged as an important class of functional nanostructures with potential applications in many diverse fields, especially in health sciences. We have used a modified aqueous sol–gel route for the synthesis of size-selective FePt@SiO2 core–shell nanoparticles. In this approach, oleic acid and olyel amine stabilized FePt nanoparticles are first encapsulated through an aminopropoxysilane (APS) monolayer and then subsequent condensation of triethoxysilane (TEOS) on FePt particle surface. These well-defined FePt@SiO2 core–shell nanoparticles with narrow size distribution become colloidal in aqueous media, and can thus be used as carrier fluid for biomolecular complexes. In comparison, the scarce hydrophilic nature of oleic acid monolayers on FePt particle surface yields an edgy partial coating of silica when only TEOS is applied for the surface modification. The synthesized core–shell nanoparticles were characterized by direct techniques of high resolution transmission electron microscopy (HRTEM), EDS and indirectly via UV–vis absorption and FTIR studies. The FePt@SiO2 nanoparticles exhibit essential characteristics of superparamagnetic behavior, as investigated by SQUID magnetometry. The blocking temperatures (T B) of FePt and FePt@SiO2 (135 and 80 K) were studied using zero field cooled (ZFC)/field cooled (FC) curves.
Keywords: FePt nanoparticles; Silica; Core–shell; Sol–gel; Colloids;

Fabricating gold nanoparticle–oxide nanotube composite materials by a self-assembly method by Jin-Zhong Xu; Wen-Bo Zhao; Jun-Jie Zhu; Gen-Xi Li; Hong-Yuan Chen (450-454).
Composition of nanostructured metal particles on oxide tubes (TiO2 and ZrO2) were fabricated and characterized. The composite materials were examined by transmission electron microscopy, scanning electron microscopy, FT-IR absorption, and UV–visible absorption spectra. The results of characterization showed that the composites indeed contained both oxide tubes and gold nanoparticles and that the gold nanoparticles were intimately associated with the nanotubes.
Keywords: Self-assemble; Au–metal oxide; Nanotube; Composition; TiO2 and ZrO2;

Comparative osmotic compression experiments were performed on colloidal silica dispersions in the presence of various chloride salts at the same 0.01 M concentration with different counterions and highlighted the influence of ionic specificity on the resistance to water removal. These results were complemented with frontal ultrafiltration measurements that demonstrate modulation of the permeate flux according to the salt used.
Keywords: Ionic specificity; Colloidal silica dispersions; Osmotic compression; Frontal ultrafiltration;

Ultrafast dynamics in a nanocage of enzymes: Solvation and fluorescence resonance energy transfer in reverse micelles by Parijat Majumder; Rupa Sarkar; Ajay Kumar Shaw; Anjan Chakraborty; Samir Kumar Pal (462-474).
In this contribution we report studies of the nature of solvation and resonance energy transfer processes in a reverse micelle (RM) upon encapsulation of a digestive enzyme, α-chymotrypsin (CHT). We have used one donor, Coumarin 500 (C500), and three acceptors Rhodamine 123 (R123, cationic), ethidium bromide (EtBr, cationic), and Merocyanine 540 (MC540, anionic). By selectively exciting the donor at the surface of the RM with a proper excitation wavelength we have examined solvation dynamics in the microenvironment. The solvation correlation function in the RM without CHT exhibits single-exponential decay with time constant ∼660 ps, which is similar to that of the CHT-included RM. However, in the case of CHT-included RM ( w 0 = 10 ) , the time-resolved anisotropy and spectral linewidth analysis of the surface-bound donor reveal the existence of an annular aqueous channel of thickness ∼2.5 Å between the enzyme surface and the inner surface of the RM. The aqueous channel is a potential host for the water-soluble substrate and also is involved in maintaining the proper functionality of RM encapsulated CHT. The studies use both steady-state and time-resolved fluorescence resonance energy transfer (FRET) techniques to measure donor–acceptor distances in the RM and also emphasize the danger of using steady-state fluorescence quenching as a method in careful estimation of the distances. The local geometrical restriction on the donor and acceptor molecules was estimated from time-resolved polarization (anisotropy) measurements. The time-resolved anisotropy of the donor and acceptor molecules also revealed significant randomization of the relative orientation of transition dipoles of the donor and acceptor, justifying the use of 2 / 3 as the value of the orientation factor κ 2 . These studies attempt to elucidate the excellence of the RM as a nanohost of biological macromolecules.
Keywords: Fluorescence resonance energy transfer (FRET); Solvation dynamics; Time-resolved anisotropy; Reverse micelle; α-Chymotrypsin; Nanocage; Enzyme; Temporal spectral width; TRES; TRANES;

Two lipophilic ligands containing triazole and hydroxyl groups, N-alkyl(C n H2n+1)-3,5-bis(hydroxymethyl)-1,2,4-triazole ( n = 10 and 12), were synthesized. Effects of their Cu(II) and Ni(II) complexes on the hydrolysis of p-nitrophenyl picolinate (PNPP) in cetyltrimethylammonium bromide (CTAB) micelles have been investigated kinetically, and some kinetic parameters of the reactions were obtained by employing the ternary complex kinetic model for metallomicellar catalysis. It was found that Cu(II) complexes of these triazole-based ligands showed more effective catalytic activity on the hydrolysis of PNPP than Ni(II) complexes. Also, the apparent first-order rate constants for product formation in the metallomicellar phase ( k N ′ ), the association constants between the substrate and the binary complex ( K T ), and the association constants between the metal ion and the ligand ( K M ) increased with an increase in pH value, which may be attributed to an increase in the nucleophilicity of the hydroxyl groups in the ligand or the electrophilicity of the substrate at higher pH. In addition, at constant pH, k N ′ and K T increased with an increase in the hydrocarbon chain length of the ligand, while K M decreased.
Keywords: Metallomicellar catalysis; Hydrolysis; Triazole; Metal complex; Kinetics;

Dissolution of kaolinite induced by citric, oxalic, and malic acids by Xingxiang Wang; Qingman Li; Huafeng Hu; Taolin Zhang; Yiyong Zhou (481-488).
Kaolinite is a dominant clay mineral in the soils in tropical and subtropical regions, and its dissolution has an influence on a variety of soil properties. In this work, kaolinite dissolution induced by three kinds of low-molecular-weight organic acid, i.e., citric, oxalic, and malic acids, was evaluated under far-from-equilibrium conditions. The rates of kaolinite dissolution depended on the kind and concentration of organic acids, with the sequence R oxalate > R citrate > R malate . Chemical calculation showed the change in concentration of organic ligand relative to change in concentration of organic acid in suspensions of kaolinite and organic acid. The effect of organic acid on kaolinite dissolution was modeled by species of organic anionic ligand. For oxalic acid, L2− oxalic and HL oxalic jointly enhanced the dissolution of kaolinite, but for malic and citric acids, HL malic and H2L citric made a higher contribution to the total dissolution rate of kaolinite than L2− malic and L3− citric, respectively. For oxalic acid, the proposed model was R Si = 1.89 × 10 −12 × [ ( 25 x ) / ( 1 + 25 x ) ] + 1.93 × 10 −12 × [ ( 1990 x 1 ) / ( 1 + 1990 x 1 ) ] ( R 2 = 0.9763 ), where x and x 1 denote the concentrations of HLoxalic and Loxalic, respectively, and x 1 = 10 −3.81 × x / [ H + ] . For malic acid, the model was R Si = 4.79 × 10 −12 × [ ( 328 x ) / ( 1 + 328 x ) ] + 1.67 × 10 −13 × [ ( 1149 x 1 ) / ( 1 + 1149 x 1 ) ] ( R 2 = 0.9452 ), where x and x 1 denote the concentrations of HLmalic and Lmalic, respectively, and x 1 = 10 −5.11 × x / [ H + ] , and for citric acid, the model was R Si = 4.73 × 10 −12 × [ ( 845 x ) / ( 1 + 845 x ) ] + 4.68 × 10 −12 × [ ( 2855 x 1 ) / ( 1 + 2855 x 1 ) ] ( R 2 = 0.9682 ), where x and x 1 denote the concentrations of H2Lcitric and Lcitric, respectively, and x 1 = 10 −11.16 × x / [ H + ] 2 .
Keywords: Kaolinite; Dissolution kinetics; Citric acid; Oxalic acid; Malic acid;

On derivatives of surface charge curves of minerals by Johannes Lützenkirchen (489-497).
Surface titrations of minerals in aqueous electrolyte solutions are used as building blocks for surface complexation modelling. However, these potentiometric data may contain less model relevant information than previously and presently assumed. In the literature, derivative analyses have been applied to experimental surface charge versus pH curves and four or more pK values were extracted for goethite or aluminium oxide. Derivative analysis of specific surface charge versus pH curves calculated for various published model variants for goethite shows that not more than the net-zero proton surface charge condition can be extracted from computer generated data. Generated data can be produced in density and precision superior to experimental data, but yield only relatively little output from such derivative analysis compared to what has previously been extracted from derivatives of experimental data. For the generated goethite data and for all model variants only the point of zero could be extracted. For the various goethite model variants tested a nearly symmetrical peak appeared at the point of zero charge in the derivative curve. A different pattern could be obtained for generic models, for which two sites with unequal sites densities and different pK values were assumed. Variation of these parameters could result in derivatives of the charging curves with two maxima or one maximum and a broad tailing. In the literature, curves with features nearly identical to these generated curves have been interpreted by up to four pK values (i.e., four different sites within a 1-pK model). It is concluded that the interpretation of the generated data is in all cases hampered by the overwhelming electrostatic contributions to the free energy of proton ad/desorption. In no case except for the one-site 1-pK model was it possible to extract the input pK value(s) from the derivatives. Plausible explanations for the discrepancy between generated data and published experimental data are discussed.
Keywords: Mineral surface charge; Surface complexation; Adsorption; Site heterogeneity;

Oxidation process induced by 2-mercaptopyrimidine at a mercury electrode by Josefa Ángela García Calzón; Jesús Luis Muñiz Álvarez; Juan Miguel López Fonseca (498-504).
The oxidation process induced by 2-mercaptopyrimidine (RSH) at a hanging mercury drop electrode was studied in aqueous media by normal and cyclic voltammetry. The results indicate the formation of a weakly adsorbed HgSR complex according to the reaction Hg + RSH → HgSR + e − + H+. When the surface excess of HgSR is high, a two-dimensional condensation takes place if the potential is positive enough, as proved by phase-sensitive ac and cyclic voltammetry.
Keywords: 2-Mercaptopyrimidine; Mercury electrode; Voltammetric techniques; Adsorption;

Activated carbons with well-developed pore structures were prepared from pistachio-nut shells by chemical activation using zinc chloride under both nitrogen atmosphere and vacuum conditions. The effects of preparation parameters on the carbon pore structure were studied in order to optimize these parameters. It was found that under vacuum conditions, the characteristics of the activated carbons produced are better than those under nitrogen atmosphere. The impregnation ratio, the activation temperature, and the activation hold time are the important parameters that influence the characteristics of the activated carbons. The optimum experimental conditions for preparing predominantly microporous activated carbons with high pore surface area and micropore volume are an impregnation ratio of 0.75, an activation temperature of 400 °C, and a hold time of 1 h. Under these conditions, the BET surface areas of the carbons activated under nitrogen atmosphere and vacuum conditions were 1635.37 and 1647.16 m2  / g, respectively. However, at a ZnCl2 impregnation ratio of 1.5, a furnace temperature of 500 °C, and a hold time of 2 h, the predominantly mesoporous activated carbon prepared under vacuum condition had a BET surface area of 2527 m2  / g. Fourier transform infrared spectra were used to detect changes in the surface functional groups of the samples during the different preparation stages.
Keywords: Activated carbon; Chemical activation; Surface areas; Pistachio-nut shell;

The study of adhesion has received considerable attention in recent years, partly due to advances in the design and fabrication of micro/nano devices. Many adhesion investigations are centered on single-spherical-contact models, which include the classic Johnson–Kendall–Roberts (JKR), improved Derjaguin–Muller–Toporov (IDMT), and Maugis–Dugdale (MD) models. Based on the IDMT single-asperity model, adhesive rough surface contact models have also been developed, which are valid for elastic and elastic–plastic contact conditions. A limitation of the IDMT-based models is that they are only valid for application cases with low adhesion parameter values. In this research, a contacting rough surface adhesion model was developed by combining an extended Maugis–Dugdale (EMD) model (which is only valid for elastic contacts) with an IDMT-based elastic–plastic adhesion model. The proposed model, termed the elastic–plastic hybrid adhesion model, is valid for the entire adhesion parameter range and also for elastic–plastic contacts. The proposed model gives results similar to the EMD rough surface model when the contact is primarily elastic. Moreover, the proposed model was compared to an IDMT-based model (ISBL model) and both gave similar results for contacts with low adhesion parameter values. With high adhesion parameter values, the ISBL model fails, whereas the proposed model correctly predicts higher adhesion. Last, based on the stiffness of the external force, the instability for adhesive rough surfaces in contact was also discussed, and it was postulated that a high peak value of the external force stiffness directly relates to the unstable contact process.
Keywords: Adhesive contact; Extended Maugis–Dugdale; Roughness; Elastic–plastic contact; Head/disk interface;

In this paper, the hypotheses proposed for the action of urea on the perturbation of molecular assemblies have been tested through studies of the effects of urea on the aggregation properties of a chiral surfactant, sodium N-(11-acrylamidoundecanoyl)-l-valinate in water. Surface tension, fluorescence, and circular dichroism were used to characterize the solution behavior of the amphiphile in the presence of urea. Surface tension measurement indicated decrease of critical aggregation concentration (cac) with the addition of urea in the low concentration range. Fluorescence probe studies using pyrene and 1-anilinonaphthalene indicated solubilization of urea molecules near the aggregate-water interface. Fluorescence anisotropy measurements using 1,6-diphenylhexatriene as probe molecule suggested increase of packing of the hydrocarbon chains of the amphiphiles upon addition of low concentration of urea. Dynamic light scattering measurements showed an increase of the hydrodynamic radius ( R h ) in the presence of increased concentration of urea. At higher concentrations of urea, the R h value decreased. Circular dichroism spectra showed the presence of chiral aggregates even in the presence of high concentration of urea.
Keywords: Urea; Chiral amino acid-derived surfactant; Hydrodynamic radius; Fluorescence anisotropy; Circular dichroism;

A multiple emulsion of the type O1/W/O2 is studied experimentally by means of differential scanning calorimetry (DSC). The aim of this work is to characterize and measure the time-dependent changes within the emulsion. In particular, interest is focused to quantify the concentration changes in the internal and external phases of the O1/W/O2 multiple emulsion. In order to accomplish the objective, the measurement and analysis carried out by DSC are based on the crystallization behavior of the emulsion. A volume of a few mm3 is periodically removed from the O1/W/O2 multiple emulsion. The sample is submitted to steady cooling and the crystallization thermogram is recorded. The experimental data provided by the crystallization thermogram makes it possible to quantify the crystallized mass for both phases, the internal and the external. In addition, the composition in each phase can also be deduced from the thermogram. To deduce the composition, a diagram of crystallization temperatures is elaborated, employing several mixtures of known composition. In addition to the main objective previously mentioned, the influence of formulation parameters such as surfactant concentration in the aqueous phase and the mass ratio of the internal and external phases are also analyzed. The experimental results made it possible to conclude that a mass transfer took place from the internal phase toward the external phase; this transfer is caused by the composition difference on both sides of the aqueous membrane. In this work we analyzed the mass transfer in the multiple emulsion carried out by a composition gradient through the aqueous membrane. The most likely mechanism of mass transfer through the aqueous membrane is a solution–diffusion of tetradecane enhanced by the micelles of the surfactant Tween 20. The model of mass transfer confirms that the osmotic pressure difference controls the kinetics of tetradecane transfer. It is also confirmed that an increment of surfactant concentration in the aqueous phase allows a faster kinetics of the tetradecane transfer.
Keywords: Multiple emulsion; Liquid membrane; Micelles; Surfactant; Differential scanning calorimetry; Mass transfer;

Rheological characterization of polysaccharide–surfactant matrices for cosmetic O/W emulsions by D. Bais; A. Trevisan; R. Lapasin; P. Partal; C. Gallegos (546-556).
Rheometrical techniques can be profitably used for polysaccharide matrices in order to evaluate their suitability for the preparation of stable cosmetic O/W emulsions. In particular, the rheological properties of aqueous scleroglucan systems were investigated under continuous and oscillatory shear conditions in a polymer concentration range (0.2–1.2% w/w) embracing the sol/gel transition. The effects due to the addition of two different surfactants (up to 10% w/w) were examined at constant polymer concentration (0.4% w/w). The selected additives are a nonionic polymeric siliconic surfactant (dimethicone copolyol) and a cationic surfactant (tetradecyltrimethylammonium bromide), respectively. Polysaccharide–surfactant interactions leading to complex formation were detected also through rheology. The combined action of both nonionic and cationic surfactants in the polymer solution was examined at two different surfactant concentration levels (5 and 10% w/w), demonstrating the beneficial effects produced on the mechanical properties of the polymer matrix by the coexistence of both surfactants. Such beneficial effects are confirmed by the stability and rheology shown by the emulsions prepared. In this way, the results point out the good agreement between the rheology of the continuous phase and the final characteristics of the emulsion obtained.
Keywords: Rheology; Emulsions; Polysaccharide matrices; Surfactants; Emulsion stability;

Self-assembly and micellization of amphiphilic rod–coil block oligomer at the mica–water interface by Hongbo Li; Bo Song; Lidong Qin; Qingtao Liu; Lixin Wu; Jiacong Shen (557-563).
In this paper, in situ atomic force microscopy has been used to investigate the micellization and self-assembling structure of an amphiphilic rod–coil block oligomer (EO16OPV) containing a conjugated oligo(phenylene vinylene) dimer and poly(ethylene oxide) at the mica–water interface. It is found that EO16OPV molecules have strong adsorption and aggregation properties on mica. In the wide concentration range from above the critical micelle concentration (cmc) to far below the cmc, a closely packed layer of stripe-like micelles with two preferred orientations can be formed at the mica–water interface. A cylindrical micelle structure for the stripes is proposed. We demonstrate that the stripe-like micelles formed on mica originate from different micellization processes at solution concentrations above and below the cmc. The origins of the strong micellization properties and oriented arrangement of the stripes are also discussed.
Keywords: Adsorption; Amphiphilic rod–coil block oligomer; Cylindrical micelles; Interface; In situ AFM; Micellization; Self-assembly;

The interaction between morin and CTAB aggregates by Weiya Liu; Rong Guo (564-573).
Electronic absorption spectra, fluorescence emission spectra, ATR-FTIR spectra, cyclic voltammetric measurements, and ab initio quantum calculation are used to study the properties of morin in CTAB micelles with different microstructures and microenvironments and to gain information about the binding of morin with CTAB micelles. Morin can be located in the CTAB micelle with its phenyl group (deviating with 38.98° from the planarity) only in the form of the monomer, which leads to increase of the planarity and extension of the π conjugation of the whole molecule. The embedding of two hydroxyl groups on the phenyl into a more hydrophobic microenvironment makes the oxidation peak of morin move to a higher potential with a decreased peak current. The binding of morin with CTAB micelles is a spontaneous ( Δ G < 0 ) and endothermic process ( Δ H > 0 ), and the hydrophobic and electrostatic force is the main driving force for its solubilization.
Keywords: CTAB micelle; Morin; Ab initio quantum calculations; Binding constant; Micropolarity; Cyclic voltammetry;

In this paper, we model frequency-dependent electro-osmosis in a capillary using the fully nonlinear Navier–Stokes equation (NSE) for viscous, incompressible, and homogeneous flow. We simulate the NSE using the finite element method, computing the solution for a closed capillary and compare it to the closed form solutions. It is confirmed that the second velocity zero crossing is dependent of the capillary radius. The distance of the zero velocity crossing decreases with decreasing capillary radius. It is also shown that the AC electro-osmosis causes a circulation of fluid within the capillary with low frequencies generating the greatest net flow.
Keywords: Frequency; AC; Electro-osmosis; Modeling; Numerical; Fem; Electro-kinetics;

This work explores the use of conformal nanoscale plasma coatings on the surface of boron nitride (BN) powders to control the rheological properties of BN/poly(dimethylsiloxane) (PDMS) composites. BN particles are conformally coated with hexafluoropropylene oxide (HFPO) in a tumbling RF-plasma reactor. Following the HFPO plasma treatment, XPS evidence indicates the presence of thin coating on the surface of the particles having a F:C ratio of 1.77. Filled BN/PDMS composites are investigated using oscillatory shear rheometry in the concentration range of 0.09–0.41 vol% (ϕ). The addition of the plasma treated BN particles to the PDMS matrix reduces the complex viscosity by 40–60% when compared with equally loaded control samples across a broad concentration range. The frequency dependence of the maximum packing fraction ( ϕ m = 0.38 – 0.42 ) is also observed for both treated and untreated particles. The maximum packing fraction does not appear to be significantly affected by the conformal plasma polymer treatment. The investigation has shown that the relative dynamic viscosity of the BN/PDMS can be described by the modified Mooney equation.
Keywords: Plasma polymerization; Fluoropolymer; Conformal coatings; Boron nitride; Highly filled polymers; Viscosity; Thermal management; Composites;

Viscosity behavior of silica suspensions flocculated by associating polymers by Masashi Kamibayashi; Hironao Ogura; Yasufumi Otsubo (592-597).
Associating polymers are hydrophilic long-chain molecules containing a small number of hydrophobic groups, and act as flocculants in aqueous suspensions. The effects of associating and nonassociating polymers on viscosity behavior are studied for silica suspensions. Since flocculation is induced by polymer bridging, the viscosity behavior is converted from Newtonian to shear-thinning profiles. The additions of surfactant cause an increase in viscosity for suspensions prepared with associating polymer, whereas the flow behavior of suspensions with nonassociating polymer is not significantly influenced. In adsorption of associating polymers onto silica particles, the chain may adopt a conformation with a water-soluble backbone attached to the particle surfaces. The hydrophobic groups extending from the chains adsorbed onto different particles can form a micelle by association with surfactant. Therefore, the bridging flocculation is enhanced by surfactant. The cooperative micellar formation between associating polymer and surfactant is responsible for viscosity increase in suspensions.
Keywords: Associating polymer; Bridging flocculation; Polyethylene glycol; Silica suspension; Viscosity;

Molecular interaction in binary surfactant mixtures containing alkyl polyglycoside by Zhong-Ni Wang; Gan-Zuo Li; Gao-Yong Zhang; Zhao-Yu Diao; Lu-Sheng Chen; Zheng-Wu Wang (598-602).
Surface tensions were measured for several binary mixtures of a multidegree polymerized alkyl polyglycoside, C12G1.46, with different types of surfactants in 0.1 M NaCl at 25 °C. Based on regular solution theory, using a dimensional crystal model and a phase separation model, the molecule exchange energy in mixed monolayer formation (ɛ) and mixed micellization ( ɛ m ) were determined. Surfactants used in the mixtures with C12G1.46 in this study are C12E3S (trioxyethylenated dodecyl sulfonate), C12TAC (dodecyl trimethylammonium chloride), BE-6 (hexaoxyethylenated trisiloxane surfactant), and TMN-6 (hexaoxyethylenated-2,6,8-trimethylnonanol). The mixtures show exchange energy in mixed monolayer formation (ɛ) and mixed micellization ( ɛ m ) ranging from −660 to −1410 J/mol, indicating a decrease in surface energy upon mixing. The decreases in surface energy are in the order C12G1.46/C12E3S > C12G1.46/C12TAC, C12G1.46/C12TAC > C12G2/C12TAC and C12G1.46/BE-6 > C12G1.46/TMN-6. The ability of the mixed monolayer formation relative to the mixed micelle formation of the same binary mixture, measured by the ( ɛ − ɛ m) values, is in the order C12G1.46/BE-6 > C12G1.46/TMN-6 > C12G1.46/C12E3S→0 > C12G1.46/C12TAC.
Keywords: Molecule exchange energy; Surfactant interaction; Surfactant mixture; Alkylpolyglycoside;

A survey is made of previously reported values of the surface shear viscosity of sodium dodecyl sulphate solution which reveals inconsistencies. The origin of these inconsistencies is thought to be due to the fact that, because SDS is a soluble surfactant, the surface deformation rate is governed by a three-dimensional sublayer adjacent to the surface and is therefore inherently experiment-dependent. Because of this, only an apparent surface shear viscosity that is specific to a particular experiment can be measured. However, for an insoluble surfactant, an intrinsic two-dimensional surface viscosity can be clearly defined. Some methods of measuring an apparent surface shear viscosity assume that the surface shear viscosity is the only surface property that determines the drainage rate from foam or individual Plateau borders but there is experimental evidence to show that other surface properties may be significant.
Keywords: Foam; Surface shear viscosity; Soluble surfactants; Drainage;

by Arthur Hubbard (607).