Journal of Colloid And Interface Science (v.289, #2)

Use of the liquid–liquid interface for generating ultrathin nanocrystalline films of metals, chalcogenides, and oxides by C.N.R. Rao; G.U. Kulkarni; Ved Varun Agrawal; Ujjal K. Gautam; Moumita Ghosh; Usha Tumkurkar (305-318).
The air–water interface has traditionally been employed to prepare particle assemblies and films of metals and semiconductors. The interface between water and an organic liquid, however, has not been investigated sufficiently for possible use in preparing nanocrystals and thin films of materials. In this article, we demonstrate the use of the liquid–liquid interface as a medium for preparing ultrathin films of metals, chalcogenides and oxides. The method involves the reaction at the interface between a metal-organic compound in the organic layer and an appropriate reagent for reduction, sulfidation, etc. in the aqueous layer. Some of the materials discussed are nanocrystalline films of gold, CuS, CuSe, CuO, and Cu(OH)2 formed at the liquid–liquid interface. The results reported in this article should demonstrate the versatility and potential of the liquid–liquid interface for preparing nanomaterials and ultrathin films and encourage further research in this area.
Keywords: Nanocrystals; Ultrathin films; Liquid–liquid interface;

Two model compounds, sodium pyrophosphate (pyro-P) and sodium tripolyphosphate (tripoly-P), were employed to elucidate the binding mechanisms of condensed phosphate on aluminum hydroxide by utilizing attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy. Peak assignments for the condensed phosphates in the solution phase and those adsorbed on the surface of aluminum hydroxide were made. Electron delocalization and polarization were employed to explain the peak shifts and the complexation of condensed phosphate with aluminum hydroxide. The tripoly-P and pyro-P were adsorbed on aluminum hydroxide by forming inner-sphere complexes. The adsorbed condensed phosphates were deprotonated in the pH range from 4 to 10. Monodentate, bidentate, and binuclear complexes were formed when pyro-P was adsorbed on aluminum hydroxide, while monodentate and binuclear complexes were formed when tripoly-P was adsorbed. Based on the FTIR data, we proposed that when either bidentate or binuclear complexes were formed, the two oxygen atoms participating in the complexation with aluminum hydroxide could not be originated from the same terminal phosphate moiety. The Al―O bond formed in the complexation of pyro-P or tripoly-P with aluminum hydroxide (AlPO 3) was not as strong as the H―O bond in terminal HPO 3. The bridging PO 2 of tripoly-P did not coordinate with aluminum hydroxide. The real-time ATR-FTIR study on condensed phosphate adsorption revealed that a long contact time between condensed phosphates and aluminum hydroxide particles can result in a transformation of an initially formed species into a thermodynamically more stable phase.
Keywords: Aluminum hydroxide; ATR-FTIR; Complexation; Condensed phosphate; Electron delocalization; Polarization;

Adsorptive interaction of p-aminophenol and p-nitrophenol in the concentration range 10 −4 – 10 −5   M and at room temperature ( 30 ± 1 ° C ) was studied with antimony, cadmium, and zirconium ferrocyanides. The interaction followed the Langmuir type of adsorption in general. The p-nitrophenol was found to have greater affinity for the antimony, cadmium, and zirconium ferrocyanides then the p-aminophenol.
Keywords: Removal; p-Aminophenol; p-Nitrophenol; Adsorption; Metal ferrocyanides;

The adsorption of basic dye (i.e., ethyl violet or basic violet 4) from aqueous solution onto the regenerated spent bleaching earth (RSBE) was carried out by varying the process parameters such as initial concentration, pH, and temperature. As analytical comparisons, activated bleaching earth (ABE) was also used as adsorbent for the adsorption of the basic dye at various initial concentrations. The experimental results showed that the adsorption process can be well described with the pseudo-second-order reaction model and less fitted by the intra-particle diffusion model. The kinetic parameters of both models obtained in the present work are in line with pore properties of the two adsorbents. According to the equilibrium adsorption capacity from the fitting of pseudo-second-order reaction model, it was further found that the both models of Langmuir and Freundlich appeared to fit well the isotherm data. In addition, the thermodynamic parameters were evaluated based on the pseudo-second-order rate constants, showing that the adsorption of ethyl violet onto the RSBE is endothermic in nature.
Keywords: Spent bleaching earth; Adsorption; Ethyl violet; Kinetic modeling; Isotherm;

Phosphorus is recognized as the most critical nutrient limiting lake productivity. The trophic status and development of lake systems are also influenced by the phosphorus content and fractions and phosphate sorption characteristics of the lake sediments. The phosphorus fractions and phosphate sorption characteristics of sediments in shallow lakes from the middle and lower reaches of Yangtze River region in China were investigated. The results show that the phosphorus contents in the sediments ranged from 217.8 to 1640 mg kg−1; inorganic phosphorus (IP) was the major fraction of total phosphorus (TP); phosphorus bound to Al, Fe, Mn oxides, and hydroxides (Fe/Al–P), and calcium bound phosphorus (Ca–P) were the main fractions of IP. Phosphate sorption on the sediments mainly occurred within 2 h and then reached equilibrium in 10 h. The phosphate sorption rate was closely related to the concentration of fine particles. The phosphate sorption capacity ranged from 128.21 to 833.33 mg kg−1, showing a significant correlation with the contents of Fe, Fe + Al, total organic carbon (TOC), cationic exchange capacity, total nitrogen, TP, Ca, IP, and the ratio of P/(Al + Fe), and it was higher in the sediments of eutrophic lakes than in mesotrophic lakes. Phosphate was mainly sorbed onto Fe and Al particles. The phosphate sorption efficiency ranged from 26.74 to 312.50 L kg−1, and had a strong positive correlation with Fe content. For the eutrophic lake sediments, there were no significant relationships between the phosphate sorption efficiency and the selected physical and chemical parameters. But for the mesotrophic lake sediments, the phosphate sorption efficiency was found to be positively related to the contents of Al and Fe + Al.
Keywords: Phosphorus fractions; Phosphate sorption; Sediment; Middle and lower reaches of Yangtze River region; Lake;

Hydrogen and methane sorption in dry and water-loaded multiwall carbon nanotubes by Li Zhou; Yan Sun; Zhiguan Yang; Yaping Zhou (347-351).
Both H2 and CH4 are clean energy sources. Adsorption was considered a measure to enhance their storage, and many efforts have been dedicated to creating novel materials including carbon nanotubes as efficient carriers for them. In order to understand the uptake mechanism and the viability of practical application, eight adsorption isotherms of H2 on a sample of multiwall carbon nanotubes were collected. The heat of adsorption was determined and an isotherm model was presented. Isotherms of CH4 on the same sample were also collected. While the adsorption on dry samples behaves similarly to that of H2, the sorption behavior of CH4 in the water-loaded sample is quite different and five times higher uptake capacity was observed in the wet sample due to the formation of methane hydrates. However, carbon nanotubes are unlikely to be used as an energy carrier due to its limited surface area and pore volume.
Keywords: Sorption; Hydrogen; Methane; Carbon nanotubes; Uptake mechanism;

Protonated biomass of the seaweed Sargassum muticum was investigated for its ability to remove cadmium(II) from aqueous solutions. In this work, a nonideal, semiempirical, thermodynamically consistent (NICCA) isotherm was proposed to fit the experimental ion binding data obtained in NaNO3 0.05 mol L−1. This model describes the competition between protons and metal ions satisfactorily. Moreover, it reflects the complexity of the macromolecular systems that take part in biosorption considering the heterogeneity of the sorbent. It was demonstrated in this work that the NICCA isotherm constitutes a great improvement with respect to a simpler Langmuir competitive equation, which was not able to describe all the experimental data satisfactorily. Potentiometric acid–base titrations in the absence of cadmium were made to estimate the maximum amount of acid functional groups (2.61 mmol g−1) and the conditional proton binding parameters, log K ˜ H (3.8) and m H (0.54). The values of the binding parameters for the cadmium ion were chosen to provide the best simultaneous description of the isotherm at pH 4.5, as well as the dependence of cadmium adsorption on pH. Values of log K ˜ Cd (3.1), n Cd (1.8), and p (0.19) in the case of the NICCA isotherm or log K Cd (2.94–3.4) for Langmuir competitive models were obtained. Kinetic experiments were performed at two different pH values (3.0 and 4.5), establishing the time dependence that represents the sorption of cadmium with a pseudo-second-order kinetic model. It was observed that 4 h is enough to ensure that the equilibrium uptake was reached.
Keywords: Biosorption; Algae; Cadmium; Sargassum muticum; Cross-link; NICCA;

Mixed micelles of sodium dodecyl sulfate (SDS) and poly(propylene oxide) methacrylate (PPOMA) have been studied in the presence of acrylamide using conductimetry, fluorescence spectroscopy, and small-angle neutron scattering (SANS) under the following conditions: (i) the SDS–acrylamide binary system in water; (ii) the SDS–acrylamide–PPOMA ternary system in water. The addition of acrylamide in SDS solutions perturbs the micellization of the surfactant by decreasing the aggregation number of the micelles and increasing their ionization degree. The variations of the various micellar parameters versus the weight ratio R=PPOMA/SDS are different in the presence of acrylamide or in pure water. These differences are much more pronounced for the lower than for the higher PPOMA concentrations. There is competition between acrylamide and PPOMA and at higher PPOMA concentration, acrylamide tends to be released from SDS micelles and is completely replaced by PPOMA.
Keywords: Mixed micelles; Sodium dodecylsulfate; Steady-state fluorescence quenching; Small-angle neutron scattering; Acrylamide; Micellar copolymerization;

Dielectric properties of Bauhinia monandra and Concanavalin A lectin monolayers, part I by Cesar A.S. Andrade; Adam Baszkin; Nereide S. Santos-Magalhães; Luana C.B.B. Coelho; Celso P. de Melo (371-378).
The dielectric properties of the galactose-binding lectins Bauhinia monandra (BmoLL) and Concanavalin A (Con A) were assessed by surface potential measurements of their spread monolayers on an aqueous subphase containing a monovalent electrolyte. For both lectins the curves of surface potential versus mean molecular area (ΔVA) and the independently recorded isotherms of surface pressure versus mean molecular area (ΠA) were shown to be pH-dependent. As the subphase pH changed from 2 to 9, a noticeable trend to higher surface pressures accompanied the compression of the monolayers. Conversely, the surface potentials values of both monolayers decreased with increasing pH. For Con A, with the single exception of the pH 9 case, lowering the pH yielded ΔV values higher than those for BmoLL. The contribution of the electric double layer ( Ψ 0 ) to the overall ΔV values at a given Π (15 mN/m) was calculated using a modified Davies equation and assuming that at this surface pressure the monolayers of both studied lectins were stable. While at all studied pHs the Ψ 0 values for Con A exceeded those calculated for BmoLL, for both lectins they were insensitive to pH changes. This provided evidence that the reorientation of lectin molecules, during compression predominantly contributed to the alteration of the overall ΔV values. The calculated Ψ 0 values made possible the evaluation of the dipole moments for BmoLL and Con A, and it has been estimated that the decrease in the pH of the subphase from 9 to 2 produced a 1.6-fold (twofold) increase in the value of for BmoLL (Con A). The differences in dielectric properties between the two film-forming lectins have been attributed to the differences in their structures. Indeed, the circular dichroism (CD) spectrum of Con A showed the predominance of β-plated sheet structures while that of BmoLL was typically rich in α-helix structures.
Keywords: Bauhinia monandra; Concanavalin A; Lectins; Monolayers; Surface potential; Dipole moments; Circular dichroism;

Mixed monolayers of Bauhinia monandra and Concanavalin A lectins with phospholipids, part II by Cesar A.S. Andrade; Adam Baszkin; Nereide S. Santos-Magalhães; Luana C.B.B. Coelho; Celso P. de Melo (379-385).
Isotherms of surface pressure and surface potential versus mean molecular area for dibehenoylphosphatidylcholine (DBPC), dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE), and dioleoylphosphatidylcholine (DOPC) monolayers were shown to be greatly modified when these lipids were cospread with either Bauhinia monandra (BmoLL) or Concanavalin A (Con A) lectins. For the binary films of DBPC, DPPC, and DPPE cospread with each of these two lectins, there was both a displacement of the Π – A and Δ V – A isotherms toward higher molecular areas relative to pure lipids and an increase in the maximum surface potential values relative to the Δ V – A relationships observed for the corresponding single-lectin systems. Both effects can be understood in terms of the occurrence of an explicit interaction between the lipids and the lectins. The plots of the corresponding compressibilities versus molecular areas reveal that, for all lipids but DOPC, the extent of this interaction was always larger for BmoLL than for Con A. The DPPC and DPPE mixed films with BmoLL differed in compressibility. Owing to the small DPPE polar headgroup, the DPPE–BmoLL film was much more incompressible than the DPPC–BmoLL mixed monolayer. However, for the DOPC–BmoLL and DOPC–Con A mixed films there was no evidence that an interaction between the lectins and the lipid took place, a fact attributed to the unsaturated character in the DOPC aliphatic chains, which leads to an expanded Π – A isotherm.
Keywords: Langmuir films; Bauhinia monandra; Concanavalin A; Lectins; Phospholipids;

Fast exopolysaccharide secretion of Pseudomonas aeruginosa on polar polymer surfaces by Santina Carnazza; Cristina Satriano; Salvatore Guglielmino; Giovanni Marletta (386-393).
The influence of the surface chemical structure and related physicochemical properties on the adhesion of P. aeruginosa has been studied for moderately hydrophobic polymers and for hydrophilic surfaces obtained by O2-plasma treatments and 50 keV Ar+ beam irradiation of poly(hydroxymethylsiloxane) and poly(ethyleneterephthalate). The surface chemical structure has been obtained by X-ray photoelectron spectroscopy, the roughness was measured by atomic force microscopy, and the surface free energy was evaluated from contact angle measurements for all the polymer substrates before and after the irradiation treatments. It is shown that a massive and unusually fast secretion of exopolysaccharides onto highly polar surfaces, corresponding to the formation of complex three-dimensional multilayers (i.e., biofilm-like structures), occurs already after 2 h of incubation. It is suggested that such highly polar surfaces can operate either by promoting, by means of a still unknown biomolecular mechanism, an early gene expression process or by mimicking the P. aeruginosa cellular walls.
Keywords: P. aeruginosa adhesion; Surface free energy; Exopolysaccharide secretion; Plasma treatment; Ion beam modification; Poly(hydroxymethylsiloxane); Poly(ethyleneterephthalate);

Solvent-induced lysozyme gels: Rheology, fractal analysis, and sol–gel kinetics by Marcelo A. da Silva; Elizabeth P.G. Arêas (394-401).
In this work, the gelation kinetics and fractal character of lysozyme gel matrices developed in tetramethylurea (TMU)-water media were investigated. Gelation times were determined from the temporal crossover point between the storage, G ′ , and loss, G ″ , moduli, as a function of the binary solvent composition and of protein concentration. The inverse dependence of the upper limit of the linear viscoelastic region ( γ 0 ) on protein concentration indicate that the lysozyme gels belong to the “strong link” kind, a gel category where interparticle links are stronger than intraparticle ones. Lysozyme gel fractal dimensions ( D f ) were determined from the analysis of rheological data according to a scaling theory by Shih et al. [Phys. Rev. A 42 (1990) 4772–4779] and were found to be compatible with a diffusion-limited cluster-aggregation kinetics (DLCA) for lysozyme gels formed at the TMU mass fraction in the binary organic–aqueous solvent, w TMU = 0.9 , and with a reaction-limited cluster aggregation kinetics (RLCA) for w TMU in the 0.6 ⩽ w TMU ⩽ 0.8 range.
Keywords: Gels; Fractals; Lysozyme; Rheology; Tetramethylurea; Protein;

The reaction between silver nitrate and poly(N-vinyl-2-pyrrolidone) (PVP) in pyridine at ambient conditions could lead to the formation of spherical nanoparticles or quadrilateral and triangular silver nanoplates, depending on the silver-to-PVP ratio used. It is proposed that the spherical Ag nanoparticles, which were formed early in the reaction, were transformed into nanoplates through an Ostwald ripening process driven by the bridging flocculation of small spherical Ag nanoparticles. This unique and hitherto unreported shape evolution process was carefully followed by a combination of techniques, viz., UV–visible spectroscopy, TEM, and powder X-ray diffraction.
Keywords: Ag nanoparticles; Poly(N-vinyl-2-pyrrolidone) (PVP); Nanoplates; Nanoprisms; Ostwald ripening;

The effect of block copolymer EPE1100 on the colloidal stability of Mg–Al LDH dispersions by Xiaoju Wang; Dejun Sun; Shangying Liu; Rui Wang (410-418).
The adsorption isotherm of block copolymer EPE1100 (polyethylene oxide–polypropylene oxide–polyethylene oxide) on the surfaces of Mg–Al LDH particles was determined through a solution depletion method combined with TOC measurement. X-ray diffraction patterns showed that the adsorption of EPE1100 molecules only occurred on the outer surfaces of LDH particles and they did not intercalate into the galleries between the layers. The adsorption of EPE1100 molecules changed the morphology of the particles. The effect of EPE1100 on the colloidal stability of LDH dispersion was investigated from three aspects: after the freezing–melting cycle, after the shearing rotations, and after the addition of electrolyte. The results indicated that the effect of EPE1100 on the colloidal stability of LDH dispersions was strongly related to the state of copolymer adsorption on LDH particle surfaces. It was inferred that the hydrated repulsive force and steric-repulsive force played important roles in determining the stability of the dispersions.
Keywords: Layered double hydroxides; Block copolymer; Colloidal stability; Adsorption;

Preparation and colloidal stability of monodisperse magnetic polymer particles by Shunchao Gu; Junya Onishi; Yoshio Kobayashi; Daisuke Nagao; Mikio Konno (419-426).
A previously proposed method was examined for producing monodisperse, submicrometer-sized magnetic polymer particles. The method applies soap-free emulsion polymerization during which Fe3O4 magnetic nanoparticles are heterocoagulated onto precipitated polymer nuclei. To chemically fix the magnetic particles to the polymer nuclei, vinyl groups were introduced on the Fe3O4 particles in a preliminary surface modification reaction with methacryloxypropyltrimethoxysilane, and methacryloxypropyldimethoxysilane (MPDMS) was added to reaction systems of the soap-free emulsion polymerization. The colloidal dispersion stability of magnetic polymer particles was improved by the addition of an ionic monomer, sodium p-styrenesulfonate (NaSS), during the polymerization. The polymerizations were carried out with styrene monomer and potassium persulfate initiator in ranges of NaSS concentrations ( 0 – 2.4 × 10 −3   M ), NaSS addition times (60–80 min), and monomer concentrations (0.3–0.6 M) at fixed concentrations of 1.6 × 10 −2   M initiator and 1.3 × 10 −2   M MPDMS for pH 4.5 adjusted with a buffer system of [CH3COOH]/[NaOH]. The addition of NaSS during the polymerization could maintain the dispersion stability of magnetic polymer particles during the polymerization. Selection of the reaction conditions enabled the preparation of colloidally stable, submicrometer-sized magnetic polymer particles that had coefficients of variation of distribution smaller than the standard criterion for monodispersity, 10%.
Keywords: Magnetic polymer particle; Polystyrene; Soap-free emulsion polymerization; Ionic monomer; Heterocoagulation; Colloidal dispersion stability;

Morphology and surface properties of fumed silicas by V.M. Gun'ko; I.F. Mironyuk; V.I. Zarko; E.F. Voronin; V.V. Turov; E.M. Pakhlov; E.V. Goncharuk; Y.M. Nychiporuk; N.N. Vlasova; P.P. Gorbik; O.A. Mishchuk; A.A. Chuiko; T.V. Kulik; B.B. Palyanytsya; S.V. Pakhovchishin; J. Skubiszewska-Zięba; W. Janusz; A.V. Turov; R. Leboda (427-445).
Several series of fumed silicas and mixed fumed oxides produced and treated under different conditions were studied in gaseous and liquid media using nitrogen and water adsorption–desorption, mass spectrometry, FTIR, NMR, thermally stimulated depolarization current (TSDC), photon correlation spectroscopy (PCS), zeta potential, potentiometric titration, and Auger electron spectroscopy methods. Aggregation of primary particles and adsorption capacity (V p) decrease and hysteresis loops of nitrogen adsorption–desorption isotherms becomes shorter with decreasing specific surface area (S BET). However, the shape of nitrogen adsorption–desorption isotherms can be assigned to the same type independent of S BET value. The main maximum of pore size distribution (gaps between primary nonporous particles in aggregates and agglomerates) shifts toward larger pore size and its intensity decreases with decreasing S BET value. The water adsorption increases with increasing S BET value; however, the opposite effect is observed for the content of surface hydroxyls (in mmol/m2). Associative desorption of water (2(Si―OH) →  Si―O―Si  + H2O) depends on both the morphology and synthesis conditions of fumed silica. The silica dissolution rate increases with increasing S BET and pH values. However, surface charge density and the modulus of zeta-potential increase with decreasing S BET value. The PCS, 1H NMR, and TSDC spectra demonstrate rearrangement of the fumed silica dispersion depending on the S BET value and the silica concentration (C SiO2 ) in the aqueous suspensions. A specific state of the dispersion is observed at the C SiO 2 values corresponding to the bulk density of the initial silica powder.
Keywords: Fumed silica; Morphology; Structural and adsorption characteristics; Synthesis; Interfacial water; Nonfreezable water; 1H NMR; TSDC; Concentrated aqueous suspension; Particle size distribution; Zeta potential; FTIR; Surface charge density; Dissolution of oxides; Water desorption;

The polymeric film grown during dopamine oxidation at an Au electrode was studied as a novel matrix for immobilizing anti-human immunoglobulin G (IgG) via the electrochemical quartz crystal impedance analysis (EQCIA) method. The growth of the polymeric films at Au electrodes during dopamine oxidation in neutral phosphate buffer (pH 7.4) and the immobilization of anti-human IgG into the polymeric films during their growth have been traced at real time. Lysozyme control experiments suggested that anti-human IgG was electrostatically incorporated into the polymeric film. Also, the porosity of the polymeric films has been discussed by measuring the “wet” and “dry” frequency shifts. Compared with a polypyrrole film immobilized with anti-human IgG, the proposed matrix possessed a larger amount of specific binding sites for human IgG by subsequent immunoreaction tests. The association constant of the anti-human IgG immunoreaction was obtained with satisfactory results.
Keywords: Electrochemical quartz crystal impedance analysis; Polymerization during dopamine oxidation; Immobilization of anti-human IgG; Human IgG; Au electrode;

Free radical generation upon plasma treatment of cotton fibers and their initiation efficiency in surface-graft polymerization by Laura Andreozzi; Valter Castelvetro; Gianluca Ciardelli; Leopoldo Corsi; Massimo Faetti; Enrico Fatarella; Fabio Zulli (455-465).
Low-temperature plasma was used to activate mercerized cotton fabrics, to be followed by grafting with various methacrylates. Careful analysis of the experimental electron spin resonance (ESR) lineshapes of cotton samples treated at different RF powers made it possible to recognize and quantify four different species of free radicals still persistent 30 h after irradiation in the samples maintained under inert atmosphere. The decay rate of these species at room temperature was also evaluated with the analysis of the time evolution of the ESR spectra. The nature of the free radical species actually involved in the monomer grafting reaction has been discussed for cotton fabrics prepared under different plasma treatment conditions by analyzing the ESR lineshapes.
Keywords: ESR; Fibers; Irradiation; Plasma grafting; Free radicals;

Vanadia-catalyzed solar photooxidation of aniline by Chockalingam Karunakaran; Sambandam Senthilvelan (466-471).
Vanadia photocatalyzes the oxidation of aniline to azobenzene in ethanol. The reaction was studied using natural sunlight and UV irradiation (365 nm) as a function of [aniline], catalyst loading, airflow rate, solvent composition, etc. The photocatalyst exhibits sustainable catalytic activity. The product formation is greater with illumination at 254 nm than at 365 nm. Electron donors such as triphenylphosphine, diphenylamine, and hydroquinone enhance the photocatalysis. The singlet oxygen quencher azide ion fails to inhibit the catalysis. The photocatalysis takes place in both protic and aprotic solvents. The mechanism of photocatalysis is discussed and the product formation analyzed using a kinetic model.
Keywords: Photooxidation; Aniline; Sunlight; UV light; V2O5;

This paper describes a unique phenomenon occurred during the calcination of ZnO powders, i.e., the ZnO particles self-assembled to form prismatic aggregates with a clear edges and faces. Field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were used to characterize the particle morphology and crystal structure of the calcined sample. The emanation thermal analysis (ETA) technique was used to monitor the changes of ZnO particle surface and subsurface microstructure irregularities and the occurrence of interparticle compaction phenomena under in situ conditions of heating and cooling. It was assumed from the ETA results that the driven force of the self-assembly of ZnO particles towards prismatic aggregates originated from the solid state diffusion and migration of grain boundaries. The photocatalytic tests indicated that the prismatic aggregates of ZnO calcined at 800 °C demonstrated a highest photocatalytic activity for acetaldehyde decomposition because of the enhancement of the surface-exposed high-active crystal face of ( 10 1 ¯ 0 ).
Keywords: Zinc oxide; Self-assembly; Emanation thermal analysis; Photocatalysis;

The influence of various monovalent cations and of divalent calcium ions on colloidal fouling strength was investigated quantitatively on a bench-scale ultrafiltration device. A higher colloidal fouling potential (k) was consistently observed with lithium chloride compared to the same ionic strengths of chlorides of other monovalent cations (Na+, K+, and Cs+). This observation was attributed to the formation of an impervious layer around the colloidal particle by lithium ions that prevented the repulsive forces due to the interaction of the silica hairs formed on the particles in the presence of water. The impact of the divalent calcium ion on the fouling potential was more complex. The fouling potential first increased with calcium ion concentration and then decreased. The maximum value of fouling potential occurred at the ionic strength corresponding to the critical coagulation concentration, which decreased with increasing colloid concentration. The colloidal fouling potential was well correlated by a bilinear relationship with colloid concentration and ionic strength for all salts tested under the critical coagulation concentration.
Keywords: Fouling potential; Ionic strength; Valence; Aggregation; Colloid concentration; Critical coagulation concentration; Quantitative;

Self-assembling structures and thin-film microscopic morphologies of amphiphilic rod–coil block oligomers by Hongbo Li; Qingtao Liu; Lidong Qin; Miao Xu; Xiankun Lin; Shengyan Yin; Lixin Wu; Zhongmin Su; Jiacong Shen (488-497).
This paper examines the influences of solvent evaporation and atmosphere humidity on self-assembling structures and thin-film microscopic morphologies of amphiphilic rod–coil block oligomers (EO n OPV) containing conjugated oligo(phenylene vinylene) dimer (OPV) coupled to poly(ethylene oxide) (PEO; n, the average number of ethylene oxides, is 16, 12, 7, and 3, respectively) on hydrophilic substrates. Atomic force microscopy (AFM), UV–vis absorption, and small angle X-ray diffraction are employed to investigate the thin-film morphology and structure. Solvent evaporation and atmosphere humidity are found to exert a strong influence on thin-film morphology and structure. Under the condition of quick evaporation and dry atmosphere, all EO n OPV oligomers form the monolayer islands. Increasing the solute volume, both EO16OPV and EO12OPV oligomers can form the polar lamellas with a head-to-tail packing arrangement. Under the condition of slow evaporation and humid atmosphere, EO16OPV and EO12OPV may self-assembly into curvy nanoribbons with well-defined width and curvature radii on mica, while EO7OPV and EO3OPV with the shorter PEO coils do not form. A symmetric bilayer structure for the ribbons is proposed. Plausible reasons for the variation in thin-film morphology are discussed, based on the results obtained from investigation of PEO coil length, solvent evaporation, and atmosphere humidity effects.
Keywords: AFM image; Humidity; Rod–coil block oligomer; Solvent evaporation; Self-assembling structure; Thin-film microscopic morphology;

Hydrogen ion titration of alkyldimethylamine oxides by 13C and 1H NMR and conventional methods by Rie Kakehashi; Motohiro Shizuma; Shingo Yamamura; Hiroshi Maeda (498-503).
In the hydrogen ion titration of micelles, the degree of ionization of the micelle at a given pH has to be evaluated to obtain a p K a value of micelles ( K a being the proton dissociation constant) at the pH. We compared the degree of ionization obtained from 13C and 1H NMR spectra with that obtained from the stoichiometric method. We used dodecyldimethylamine oxide (C12DMAO) and hexyldimethylamine oxide (C6DMAO) to examine the titration behavior of micelles and monomers, respectively. We determined p K a values of amine oxides both in H2O and D2O. As to the monomer (C6DMAO), the degree of ionization from NMR, α NMR, coincided with that from the conventional stoichiometric method α. The difference of p K 1 of amine oxide monomer between D2O and H2O was about 0.5: pK 1(D) ≈ pK 1(H) + 0.5. The difference was about the same as that for carboxylic acids. As to the C12DMAO micelle, α NMR did not coincide with α over a considerable range of α. The NMR chemical shift might be influenced by micellar structure changes induced by the ionization, such as the sphere-to-rod transition. The intrinsic logarithmic dissociation constants of the micelle were 5.9 ± 0.1 for H2O, and 6.5 ± 0.1 for D2O.
Keywords: Hydrogen ion titration; Mixed micelles; Amine oxides; NMR titration; Degree of ionization of micelles; Dissociation constant in D2O;

We have studied the phenomenon of calcium complexation by lab synthesized amphiphilic (α-aminoalkyl)-phosphonocarboxylic or -phosphonic acids. The electrical conductivity of aqueous solutions of sodium salts of all these acids was measured versus the volume of a calcium salt solution added. It appeared that calcium complexes are formed in a Ca/P atomic ratio close to 1. Calcium phosphonocarboxylates and calcium phosphonates were also precipitated by mixing aqueous solutions of disodium salts of phosphorus amphiphiles and calcium nitrate solutions. Before chemical analysis, these complexes were calcined to remove the organic part. In the mineralized products, calcium and phosphate were assayed: the Ca/P atomic ratio was equal to 1. X-ray diffraction and IR spectroscopy showed that they are made entirely of β pyrophosphate (Ca2P2O7), a result in agreement with previous chemical analysis. The chemical formula of the starting calcium complexes could be written as CaL⋅2H2O (L = ligand). The SEM micrographs of these complexes show plate-like structures. XRD patterns are characteristic of layered structures. These facts suggest that calcium complexes are composed of alternating bimolecular layers of calcium alkylphosphonocarboxylates or calcium alkylphosphonates, the chains being tilted and partially interdigitated.
Keywords: Calcium (α-aminoalkyl)-phosphonates; Calcium (α-aminoalkyl)-phosphonocarboxylates; Conductimetric study; Layered structures;

In researching the properties of surfactants, lipophobicity is an important consideration. Increasing surfactant lipophobicity corresponds to a decrease in the saturation concentration of a singly dispersed surfactant in oil, i.e., a decrease in the critical micelle concentration in oil (CMC(oil)). This, in turn, is the crucial property in discussing the efficiency of a surfactant. Lipophobicity is influenced by the structure and length of the hydrophilic moiety of the surfactant. Surfactants that consist of ―OH or C=O groups are effective for use in both aliphatic and aromatic hydrocarbon-rich systems because they are highly lipophobic and of a compact size and function independent of temperature. These characteristics are also reflected in their phase behavior. Phase diagrams illustrate the following properties: temperature independence; strong absorption at the water–oil interface and efficient action even with a very small amount of surfactant with a low CMC; high solubilization of water and oil into an aggregated surfactant solution phase. Through phase diagrams, the CMC(oil) of R10EO8 was obtained and the result used to compare the many different characteristics of the more typical oxyethylene nonionic surfactants with the new polyglyceryl nonionic surfactants.
Keywords: Lipophobicity; Glyceryl nonionic surfactant; Polyoxyethylene nonionic surfactant; Amphiphobicity; Aromatic hydrocarbon; HLB temperature;

Mixed micelles of alkylamines and cetyltrimethylammonium chloride by L. García-Río; J.R. Leis; J.L. López-Fontán; J.C. Mejuto; V. Mosquera; P. Rodríguez-Dafonte (521-529).
The influence of chain length and the nature of the head group on the composition of micelles of a binary mixture of cetyltrimethylammonium chloride with both unsubstituted and N-substituted n-octyl, n-decyl, and n-lauryl amines was established from the variation of the critical micelle concentration (cmc) as a function of the solution composition. A synergistic effect was observed in all instances that were found to be correlated with chain length and the type of N-substituent on the alkylamine head group. Experimental data were compared with theoretical predictions based on the equilibrium between micelles and monomers in solution. The Motomura treatment was used to determine the composition of each compound in the mixed micelles ( X ¯ i m ). Mixing nonideality was expressed in terms of the molecular interaction parameter ( β 12 ) as determined using the theory of Holland and Rubingh. Finally, the molecular thermodynamic model for mixed surfactant systems developed by Puvvada and Blankschtein was used to estimate the micellization free energy ( Δ G M ) and to evaluate the synergistic phenomenon.
Keywords: Mixed micelle; cmc; Amine; Micellization energy;

Physicochemical studies on microemulsions by Indranil Chakraborty; Satya P. Moulik (530-541).
Both volume- and temperature-induced percolation of conductance of w/o microemulsions formed with AOT in cyclic aliphatic and aromatic oils (cyclohexane, cyclohexanone, toluene, and xylenes), and volume percolation of water/AOT/oil systems using linear aliphatic hydrocarbons (n-hexane, n-heptane, n-octane, i-octane, and n-decane) have been studied. The effect of additives, viz. sodium cholate (NaC), sodium deoxycholate (NaDC), cholesterol, n-butanol, and t-butanol, toluene, and xylenes (o, m, and p) on the temperature-induced percolating processes using the oils cyclohexane and cyclohexanone has been examined. The percolation results have been analyzed in the light of scaling equation, and the energy of activation of the ion-transport phenomenon has been evaluated for both pre- and postpercolation stages. From the percolation data, the diameter of the microdispersed water droplets, their population, and surface area have been estimated. The enthalpy of dispersion of water in AOT/oil medium has been determined from isothermal titration calorimetric (ITC) measurements.
Keywords: Volume and temperature percolation; Cyclic and aliphatic hydrocarbon oils; AOT; Thermodynamics; Microcalorimetry;

The cell glycocalyx is an attractive model for surface modification of liposomes, because its hydrated oligosaccharide layer inhibits nonspecific protein adsorption and can provide specificity towards desired sites. Here, we report on the use of lactose as a model saccharide to modify the liposome surface and examine the vesicle size and stability. Two kinds of lactosyl lipids, including lactosyl ether-lipid (6a) and lactosyl ester-lipid (6b), which contain octadecyl and octadecanoyl as the lipid tails, respectively, were synthesized and their liposomes were prepared by the extrusion method. The effects of glycolipid structure, concentration, and the pore size of the extrusion membrane on vesicle size and stability were investigated at room temperature by photon correlation spectroscopy (PCS). All liposomes with 5 or 10 mol% of lactosyl lipids had a narrow size distribution and remained stable at room temperature for at least one month, which is comparable to 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)- and poly(ethylene glycol) (PEG)-liposomes. The maximum incorporation of lactosyl ester-lipid into liposomes was 15 mol%, compared with only 10 mol% for the lactosyl ether-lipid. The lactosyl ester-liposomes had better stability and exhibited less size change than the lactosyl ether-liposomes at 15 or 20 mol% of lactosyl lipids incorporated. This may be attributed to the better structural compatibility of lactosyl ester-lipid with DSPC. The PCS results show that the glycolipid structure and concentrations are major factors that affect vesicle stability, while the pore size of extrusion membranes has no influence.
Keywords: Liposomes; Lactose; Glycolipids; Surface modification; Cell glycocalyx;

Steady state fluorescence measurements have been carried out for binary mixtures of a series of monomeric cationic (MC), zwitterionic (ZI), dimeric cationic (DC), and twin-tail cationic (TC) surfactants with sugar (β-C8G and β-C12G) over the whole mole fraction range using pyrene as fluorescence probe. The cmc values thus determined for all the binary mixtures have been further evaluated using the regular solution theory. The various micellar parameters, such as micelle mole fraction ( X 1 ), regular solution interaction parameter (β), micropolarity, and mean micelle aggregation number (N agg), have been determined for all these series of mixtures. Variation in all these micellar parameters demonstrates that mixed micelles of these surfactants with β-C8G are mostly synergistic in nature and the synergism increases with the increase in hydrophobicity of the cosurfactant in each case. The mixtures of β-C12G with various cosurfactants do not show this behavior and instead of it, they show an increase in antagonism with the increase in hydrophobicity of cosurfactants. This discrepancy has been attributed to a large difference in hydrophobicity between β-C8G and β-C12G, and the chain folding of the latter is considered to be the reason for the antagonism.
Keywords: Mixed micelles; Sugar surfactants; Cationic surfactants; Fluorescence studies; Synergism;

Area per surfactant molecule values of gemini surfactants at the liquid–hydrophobic solid interface by Martin Pisárčik; Milton J. Rosen; Mária Polakovičová; Ferdinand Devínsky; Ivan Lacko (560-565).
Areas per surfactant molecule at the liquid/hydrophobic solid ( A LS ) and the liquid/air ( A LA ) interface as a function of the spacer length are reported for cationic gemini surfactants having ―(CH2) n ― spacer s. A LA increases with increasing spacer length up to 6–8 ―CH2 ― groups in the spacer and then levels off. A LS values indicate a more closely packed arrangement of the surfactant molecules than that at the liquid/air interface. Comparison of A LA and A LS values indicates that the surfactant molecules at the liquid/hydrophobic solid interface are almost three times as closely packed as those at the liquid/air interface. A comparison of the experimental values of the area per surfactant molecule at both interfaces was made with those calculated from dimensions of the surfactant molecule in vacuo.
Keywords: Gemini surfactant; Surfactant spacer; Area per surfactant molecule; Surface tension;

Surfactant tail length-dependent lipase activity profile in cationic water-in-oil microemulsions by Antara Dasgupta; Debapratim Das; Rajendra Narayan Mitra; Prasanta Kumar Das (566-573).
The catalytic activity of Chromobacterium viscosum lipase (CV-lipase) was estimated across varying surfactant tail lengths (C-10–C-18) in water-in-oil (w/o) microemulsions of cationic surfactants containing four different hydroxyethyl-substituted head groups. An attempt to find a correlation, if any, between the activity of interfacially solubilized lipase and the varying surfactant tails was made for the first time in micellar enzymology. The second-order rate constant, k 2 , in lipase-catalyzed hydrolysis of p-nitrophenyl-n-hexanoate at pH 6.0 and 25 °C shows an improvement in enzyme activity (∼30–140%) across different head groups of amphiphiles with increasing tail lengths in varying solution compositions. Improvement of enzyme activity is prominent in ascending from C-10 to C-14/C-16, depending on the nature of polar head group. The hydrolytic activity of lipase in different surfactant (50 mM)/water/isooctane/n-hexanol with varying z= [alcohol]/[surfactant] (6.4 or 4.8) was amplified by 25–250% with increment in surfactant tail length in comparison with widely used cationic w/o microemulsions having solution compositions ( z = 16 ) . As a notable outcome of this research, we found w/o microemulsions of 25 mM tetradecyltrimethylammonium bromide/water/isooctane/n-hexanol ( z = 8 ) producing the highest ever activity of lipase in any w/o microemulsions.
Keywords: Amphiphiles; Enzymes; Packing parameter; Reverse micelles; Surfactant tail;

Example of an organic reaction in a Langmuir film: Reduction of an amphiphilic ketone by NaBH4 by Ignacio Gascon; Cosmin Patrascu; Jean-Daniel Marty; Christophe Mingotaud (574-580).
Langmuir monolayers of an amphiphilic ketone 1 have been studied on pure water and on aqueous subphases containing sodium borohydride. Changes in the compression isotherm and in the monolayer morphology were observed when the concentration of NaBH4 or the delay between spreading and compression was increased. These modifications were specific to NaBH4 and suggested that a chemical reaction is taking place along the monolayer. Modifications in the IR spectrum of the corresponding Langmuir–Blodgett film confirmed the reduction of the ketone group of 1 when spread on aqueous subphases of sodium borohydride. Analysis of the compression isotherms demonstrated that this reaction occurred for all surface pressures and therefore indicated that the ketone group of 1 is accessible to the borohydride whatever the compression state of the monolayer.
Keywords: Langmuir film; Chemical reaction; Reduction; Brewster angle microscopy; Transition;

We study the surface adsorption and bulk micellization of a mixed system of two nonionic surfactants, namely, ethylene glycol mono-n-dodecyl ether (C12E1) and tetraethylene glycol mono-n-tetradecyl ether (C14E4), at different mixing ratios at 15 °C. The pure C14E4 monolayer cannot show any indicative features of phase transition because of both hydration-induced and dipolar repulsive interactions between the bulky head groups. On the other hand, the monolayers of pure C12E1 and its mixture with C14E4 undergo a first-order phase transition, showing a variety of surface patterns in the coexistence region between the liquid expanded (LE) and liquid condensed (LC) phases under the same experimental conditions. For pure C12E1, the domains are of a fingering pattern while those for the C12E1/C14E4 mixed system are found to be compact circular and small irregular structures at 2:1 and 1:1 molar ratios, respectively. The critical micelle concentration (cmc) values of both the pure and the mixed systems were measured to understand the micellar behavior of the surfactants in the mixture. The cmc values of the mixed system were also calculated assuming ideal behavior of the surfactants in the mixture. The experimental and calculated values are found to be very close to each other, suggesting an almost ideal nature of mixing. The interaction parameters for mixed monolayer and micelle formation were calculated to understand the mutual behavior of the surfactants in the mixture. It is observed that the interaction parameters for mixed monolayer formation are more negative than those of micelle formation, indicating a stronger interaction between the surfactants during monolayer formation. It is concluded that since both the surfactants bear EO units in their head groups, structural parity and hydrogen bonding between the surfactants allow them to be closely packed during monolayer and micelle formation.
Keywords: Brewster angle microscopy; Monoionic surfactants; Adsorbed monolayers; Critical micelle concentration;

Single-crystalline CuO nanobelts fabricated by a convenient route by Xinyu Song; Haiyun Yu; Sixiu Sun (588-591).
A reverse micelle-assisted route for preparing CuO nanobelts from precursor Cu(OH)2− 4 is reported. The reverse micelles were used as microreactors, which led to anisotropic growth crystals during a simple solvothermal process. The formation conditions of the CuO nanobelts were also studied.
Keywords: CuO nanobelts; The reverse micelles; Solvothermal process;

Electrokinetic and adsorption studies of alumina suspensions using Darvan C as dispersant by Bimal P. Singh; Sarama Bhattacharjee; Laxmidhar Besra; D.K. Sengupta (592-596).
The electrokinetic and adsorption characteristics of alumina suspensions in the presence of Darvan C as dispersant have been investigated. The interaction of Darvan C with alumina has been interpreted in terms of electrokinetic and adsorption measurements. The adsorption density of Darvan C increases greatly with decreasing pH. The isoelectric point (iep) of the sample under investigation is found to be located at pH 9.1. For pH values near and below the point of zero charge, there is an added electrostatic attractive potential for adsorption, which results in high-affinity adsorption behavior. Possible mechanisms of interaction between alumina and Darvan C are described and discussed.
Keywords: Dispersion; Surface charge; Alumina; Adsorption; Electrokinetics; Dispersant;

Pioneer studies on HCl and silylation treatments of chrysotile by Efrain Mendelovici; Ray L. Frost (597-599).
In the light of some recent studies on organosilicon derivatives of HCl-leached chrysotile, pioneer works not cited in this area are chronologically and briefly commented on, emphasizing the infrared spectroscopy (FTIR–PAS) characterization of such chrysotile products. The latter have opened a far-reaching potential for the development of, e.g., highly stable hydrophobic or organophilic materials, including fibrous sheet polymers.
Keywords: Chrysotile; HCl and silylation treatments; FTIR–PAS;

This paper presents a new model of dispersion of components in transport processes. It is suggested that the flow velocity may be specified by a Gauss function with relative dispersion of flow velocity β = σ v / v ; the overall dispersion of inert component (in porous as well as in homogeneous medium) may be calculated from the equation σ = ( 2 D t / τ 2 + ( β v t ) 2 ) 0.5 , where D is the diffusion coefficient, t is time, τ is tortuosity, and v is flow velocity. The most common range of variability of relative dispersion of flow velocity in natural soils is 8–32%. The model is well applicable to column and field experiments.
Keywords: Transport phenomena; Porous media; Diffusion; Dispersion; Dispersivity; Porosity; Tortuosity; Gauss function;

by Arthur Hubbard (604).