Journal of Colloid And Interface Science (v.307, #2)

The use of a natural palygorskite clay for the removal of Pb(II) from aqueous solutions for different contact times, pHs of suspension, and amounts and particle sizes of palygorskite clay were investigated. The variations of the pH value of Pb(II) solutions on natural palygorskite in the adsorption process were determined. Batch adsorption kinetic experiments revealed that the adsorption of Pb(II) onto palygorskite clay involved fast and slow processes. It was found that the adsorption mechanisms in the lead/palygorskite system follow pseudo-second-order kinetics with a significant contribution from film diffusion. SEM observations demonstrated that an important interaction at the lead–granule interface occurred during the adsorption process. The adsorption isotherms were described by means of the Langmuir and Freundlich isotherms and the Langmuir model represents the adsorption process better than the Freundlich model. The maximum adsorption capacity of Pb(II) onto natural palygorskite was 104.28 mg g−1.Pb(II) adsorption onto palygorskite clay occurs firstly at pores between particle aggregates, and then reaches complete equilibrium for some interactions such as palygorskite and water, complexation and ion-exchange during adsorption process.
Keywords: Lead; Palygorskite clay; Adsorption capacity; Kinetic; Isotherm;

Illite samples from Fithian, IL were purified and saturated with Na+ ions. The acid–base surface chemistry of the Na-saturated illite was studied by potentiometric titration experiments with 0.1, 0.01, and 0.001 M NaNO3 solutions as the background electrolyte. Results showed that the titration curves obtained at different ionic strengths did not intersect in the studied pH range. The adsorption of Cd(II), Cu(II), Ni(II), Pb(II), and Zn(II) onto illite was investigated as a function of pH and ionic strength by batch adsorption experiments. Two distinct mechanisms of metal adsorption were found from the experimental results: nonspecific ion-exchange reactions at lower pH values on the basal surfaces and ‘frayed edges’ and specific adsorption at higher pH values on the mineral edges. Ionic strength had a greater effect on the ion-exchange reactions. The binding constants for the five heavy metals onto illite were determined using the least-square fitting computer program FITEQL. Linear free energy relationships were found between the surface binding constants and the first hydrolysis constants of the metals.The adsorption of Cd(II), Cu(II), Ni(II), Pb(II), and Zn(II) onto illite was investigated as a function of pH and ionic strength. A two sites complexation model for illite was developed to fit the adsorption data.
Keywords: Adsorption; Cadmium; Copper; Nickel; Lead; Zinc; Illite; Surface complexation; Constant Capacitance Model; Linear free energy relationships;

Removal of Reactofix Navy Blue 2 GFN from aqueous solutions using adsorption techniques by Vinod Kumar Gupta; Rajeev Jain; Shaily Varshney; Vipin Kumar Saini (326-332).
The wheat husk, an agricultural by-product, has been activated and used as an adsorbent for the adsorption of Reactofix Navy Blue 2 GFN from aqueous solution. In this work, adsorption of Reactofix Navy Blue 2 GFN on wheat husk and charcoal has been studied by using batch studies. The equilibrium adsorption level was determined to be a function of the solution pH, adsorbent dosage, dye concentration and contact time. The equilibrium adsorption capacities of wheat husk and charcoal for dye removal were obtained using Freundlich and Langmuir isotherms. Thermodynamic parameters such as the free energies, enthalpies and entropies of adsorption were also evaluated. Adsorption process is considered suitable for removing color, COD from waste water.Plots of pH vs % color removal for Reactofix Navy Blue 2 GFN for charcoal and wheat husk.
Keywords: Azo dyes; Reactofix Navy Blue 2 GFN; Adsorption; Wheat husk;

Selenite adsorption on water-washed manganese nodule leached residues (WMNLR) was studied with the aim of detoxifying industrial effluents before their safe disposal into the environment. WMNLR, a solid waste material, was characterized with the help of XRD, FTIR, TG-DTA, pHpzc, BET surface area, surface oxygen, surface hydroxyl group, and chemical analyses. The adsorption behavior of WMNLR toward selenite was studied as a function of time, pH, temperature, and concentration of adsorbate and adsorbent. Increased adsorption capacity with rise in temperature indicates that the adsorption process was endothermic in nature. Based on the thermodynamic parameters such as the Gibbs free energy change, standard enthalpy change, and standard entropy change, the adsorption process was found to be spontaneous and endothermic in nature. Adsorption followed second-order kinetics. The adsorption capacity of the material was found to be 54.6 mg g−1 at 60 mg L−1 of selenite concentration at pH 5 in 3 h contact time.The adsorption capacity increases with increases in temperature. The adsorption process is endothermic in nature as adsorption capacity increases with increase in temperature. The enhancement in adsorption capacity may be due to chemical interaction between adsorbate and adsorbent. Positive value of enthalpy ( Δ H o ) indicates the endothermic nature of the adsorption process meanwhile positive values of entropy ( Δ S o ) suggest the increased randomness at solid–solution interface.
Keywords: Manganese nodule leached residues; Selenite; Adsorption; Langmuir isotherm; Thermodynamic and kinetic parameters;

Fluorescence and interactions with thiol compounds of Nile Red-adsorbed gold nanoparticles by Kun-Hong Lee; Shih-Ju Chen; Jing-Yueh Jeng; Yu-Ching Cheng; Jen-Taie Shiea; Huan-Tsung Chang (340-348).
We have investigated the interactions between a variety of thiols and Nile Red-adsorbed gold nanoparticles (NRAuNPs). After adding thiols to solutions of NRAuNPs, the solutions fluoresce strongly as a result of the displacement of a Nile Red-derived product from the surface of the AuNPs. We propose a mechanism for the formation of this NR product on the surface of AuNPs by conducting mass spectrometry, fluorescence, and capillary electrophoresis measurements. By recording the fluorescence changes of the NRAuNP solutions after addition of the thiols, we investigated the interactions between the thiols and NRAuNPs. Using the Langmuir isotherm model, we found that the displacement rate constants for thiols having one carboxyl residue, such as 3-mercaptopropionic acid, fall within the range 0.55 – 1.19 × 10 −2   s −1 . Thiols containing hydroxyl groups [e.g., 2-mercaptoethanol (2-ME)] or amino groups [e.g., N-(2-mercaptopropionyl)glycine (MPG)], or that have flat structures on the AuNP surface, such as mercaptosuccinic acid, exhibit double-exponential kinetics with first rate constants of 0.51 – 2.83 × 10 −2   s −1 and second rate constants of 6.0 – 23.4 × 10 −4   s −1 . Our results reveal that steric effects and the charge density of the thiols both play important roles in determining the interactions with NRAuNPs. The interactions (displacement and/or induced aggregation) are also dependent on the size of NRAuNPs.A cartoon representation of the displacement by thiols of the NR products adsorbed on AuNPs. Thiols possess k 1 and k 2 values.
Keywords: Adsorption; Fluorescence; Gold nanoparticle; Kinetic; Nile Red; Thiol;

The adsorption–desorption process of bovine serum albumin on carbon nanotubes by Laura E. Valenti; Pablo A. Fiorito; Carlos D. García; Carla E. Giacomelli (349-356).
The aim of this work is to study the adsorption–desorption process of bovine serum albumin (BSA) on carbon nanotubes (CNT) by reflectometry. The effect of the surface properties was analyzed by comparing the behavior of BSA on silica. The experiments were performed by reflectometry at different BSA concentrations, at pH 3.0, 4.8, and 7.0 and at two ionic strengths. Protein desorption was induced by either dilution with buffer or the addition of SDS. The initial adsorption rate is controlled by the attachment of BSA molecules to the surface, and strongly diminishes at pH 7. Adsorption isotherms reflect the high affinity of BSA for both sorbent surfaces and reach well-defined plateau values that depend on the pH, being the highest at pH 4.8 on CNT. Experiments performed at different ionic strengths (NaCl added) showed a less pronounced effect. Dilution does not induce desorption on either surface however, the addition of SDS removes protein only from the silica surface.The aim of this work is to study the adsorption–desorption process of bovine serum albumin (BSA) on carbon nanotubes (CNT) under different analytical conditions.
Keywords: Carbon nanotubes; Bovine serum albumin; Reflectometry;

Adsorbed para-nitrophenol on HDTMAB organoclay—A TEM and infrared spectroscopic study by Qin Zhou; Ray L. Frost; Hongping He; Yunfei Xi; Hongwei Liu (357-363).
para-Nitrophenol adsorbed on hexadecyltrimethylammonium bromide modified montmorillonite has been studied using a combination of X-ray diffraction TEM and infrared spectroscopy. Upon formation of the organoclay, the properties change from hydrophilic to hydrophobic. It is proposed that para-nitrophenol is adsorbed onto the water in the cation hydration sphere of the organoclay. As the cation is replaced by the surfactant molecules the para-nitrophenol replaces the surfactant molecules in the clay interlayer. Significant changes in the water vibrations occur in this process. Bands attributed to CH stretching and bending vibrations in general decrease as the concentration of the surfactant (CEC) increases up to 1.0CEC. After this concentration the bands increase approaching a value the same as that of the surfactant. Strong changes occur in the HCH deformation modes of the methyl groups of the surfactant. These changes are attributed to the methyl groups locking into the siloxane surface of the montmorillonite. Such a concept is supported by changes in the SiO stretching bands of the montmorillonite siloxane surface. This study demonstrates that para-nitrophenol will penetrate into the untreated clay interlayer and replace the intercalated surfactant in surfactant modified clay, resulting in the change of the arrangement of the intercalated surfactant.The mechanism of adsorption of para-nitrophenol on both non-treated montmorillonite and the surfactant intercalated montmorillonite was studied by a combination of TEM and infrared spectroscopy. On the untreated and low CEC intercalated montmorillonite the para-nitrophenol adsorbed on the cation hydration sphere. At high CEC values the para-nitrophenol replaced the surfactant cation in the interlayer and bonded directly to the siloxane surface.
Keywords: Adsorption; Intercalation; Montmorillonite; Organoclay; Infrared spectroscopy; X-ray diffraction; para-Nitrophenol; TEM;

Organically modified montmorillonites obtained by cation exchange from the same natural layered silicate were studied. The surface properties of the pristine and a series of organically modified clays were determined by inverse gas chromatography and the water adsorption mechanisms were studied by a gravimetric technique coupled with a microcalorimeter. A significant increase of the specific surface area, a decrease of the water adsorption, and a decrease of the dispersive component of the surface energy were observed when the sodium cations of the natural montmorillonite were exchanged for a quaternary ammonium. Slighter differences in surface properties were observed, on the other hand, between the different types of organically modified montmorillonites. Indeed, similar dispersive components of the surface energy were determined on the organoclays. Nevertheless, the specific surface area increased in the range 48–80 m2/g with increasing d-spacing values and the presence of specific groups attached to the quaternary ammonium, such as phenyl rings or hydroxyl groups, led to some specific behaviors, i.e., a more pronounced base character and a higher water adsorption at high activity, respectively. Differences in interlayer cation chain organization, denoted as crystallinity, were also observed as a function of the nature of the chains borne by the quaternary ammonium. In a later step, polyethylene-based nanocomposites were prepared with those organically modified montmorillonites. The clay dispersion and the barrier properties of the nanocomposites were discussed as a function of the montmorillonite characteristics and of the matrix/montmorillonite interactions expected from surface energy characterization.Evolution of γ s d values versus temperature for the different organomodified montmorillonites (○, ■, *) and polyethylene (–) explaining, in part, the formation of organoclay/polyethylene microcomposites with a weak interphase.
Keywords: Montmorillonites; Water adsorption; Surface energy; Nanocomposites; Gas permeability; Morphology;

Octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane (OpePOSS) was used as a nanocrosslinking agent to prepare the crosslinked poly(N-isopropylacrylamide) (PNIPAM) networks with POSS content up to 50 wt%. The inter-component crosslinking was achieved via the reaction between N―H moieties in amide group of PNIPAM and epoxide groups of OpePOSS. When the organic–inorganic nanocomposites were swollen in water the POSS-crosslinked PNIPAM exhibited the characteristics of hydrogels. With the moderate contents of POSS, the POSS-containing hybrid hydrogels displayed much faster response rates in swelling, deswelling and reswelling experiments than the PNIPAM hydrogels prepared via the free radical copolymerization of N-isopropylacrylamide (NIPAM) and N , N ′ -methylenebisacrylamide (viz. the conventional crosslinker). The improved hydrogel properties have been interpreted on the basis of the formation of the nanosized hydrophobic microdomains around the POSS moieties (i.e., the nanocrosslinking sites).Octa(propylglycidyl ether) polyhedral oligomeric silsesquioxane was used as a nanocrosslinker to prepare organic–inorganic poly(N-isopropylacrylamide) (PNIPAM) hydrogels. The hybrid hydrogels displayed much faster rates of swelling, deswelling and reswelling than control PNIPAM hydrogel.
Keywords: Poly(N-isopropylacrylamide); Polyhedral oligomeric silsesquioxane; Nanocomposites; Hydrogels;

The theoretical basis of a recent theory of Brownian relativity for polymer solutions is deepened and reexamined. After the problem of relative diffusion in polymer solutions is addressed, its two postulates are formulated in all generality. The former builds a statistical equivalence between (uncorrelated) timelike and shapelike reference frames, that is, among dynamical trajectories of liquid molecules and static configurations of polymer chains. The latter defines the “diffusive horizon” as the invariant quantity to work with in the special version of the theory. Particularly, the concept of universality in polymer physics corresponds in Brownian relativity to that of covariance in the Einstein formulation. Here, a “universal” law consists of a privileged observation, performed from the laboratory rest frame and agreeing with any diffusive reference system. From the joint lack of covariance and simultaneity implied by the Brownian Lorentz–Poincaré transforms, a relative uncertainty arises, in a certain analogy with quantum mechanics. It is driven by the difference between local diffusion coefficients in the liquid solution. The same transformation class can be used to infer Fick's second law of diffusion, playing here the role of a gauge invariance preserving covariance of the spacetime increments. An overall, noteworthy conclusion emerging from this view concerns the statistics of (i) static macromolecular configurations and (ii) the motion of liquid molecules, which would be much more related than expected.Relevant quantities in Brownian relativity: Diffusion coefficients of the liquid ( D ′ ) and chain ( D ″ ) molecules; relative (D) and laboratory ( D 0 ) diffusion coefficients; molecular ( Δ ′ ) and macromolecular ( Δ ″ ) diffusive horizons.
Keywords: Polymer solutions; Universal scaling; Configurational chain statistics; Brownian motion and diffusion; Brownian relativity;

Adsorption of water-soluble polymers with surfactant character. by Ana M. Díez-Pascual; Aurora Compostizo; Amalia Crespo-Colín; Ramón G. Rubio; Reinhard Miller (398-404).
A comparative study between Langmuir and Gibbs monolayers of a hyperbranched polyol, poly(propylene glycol) homopolymers, and poly(propylene glycol)–poly(ethylene glycol) copolymers with different structure and molecular weight, is reported. Dynamic surface tension (DST) and surface pressure measurements have been carried out to characterize these amphiphilic water-soluble polymers. The adsorption kinetics results are consistent with a rapid diffusion stage followed by a slow reorganization at the air–water interface. The characteristic times of these steps, calculated by the Joos model, point out differences among the polymers in the diffusion rate and rearrangement mechanisms for diluted solutions. Short time analysis of DST data leads to diffusion coefficients in qualitative agreement with the diffusion times calculated with Joos' model. Spread monolayers remain stable for long periods of time. The desorption process seems quite inoperative. As a consequence, the surface pressure of the spread monolayers can be studied over a broad surface concentration range. 2D first-order phase transitions have been evidenced from plateaux observed in Langmuir and Gibbs isotherms. It has been found that Gibbs monolayers lead to lower surface tension states than the Langmuir ones.
Keywords: Adsorption; Surfactant polymer; Air–water interface; Monolayer; Diffusion; Phase transition; Kinetics; Isotherms;

Silica gel bearing isonicotinamide groups was prepared by further modification of 3-aminopropyl-functionalized silica by a reaction with isonicotinic acid and 1,3-dicyclohexylcarbodiimide to yield 3-isonicotinamidepropyl-functionalized silica gel (ISNPS). This support was characterized by means of infrared spectroscopy, elemental analysis, and specific surface area. The ISNPS was used to immobilize the [Ru(NH3)4SO3] moiety by reaction with trans-[Ru(NH3)4(SO2)Cl]Cl, yielding [Si(CH2)3(isn)Ru(NH3)4(SO3)]. The related immobilized [Si(CH2)3(isn)Ru(NH3)4(L)]3+/2+ (L = SO2, SO2− 4, OH2, and NO) complexes were prepared and characterized by means of UV–vis and IR spectroscopy, as well as by cyclic voltammetry. Syntheses of the nitrosyl complex were performed by reaction of the immobilized ruthenium ammine [Si(CH2)3(isn)Ru(NH3)4(OH2)]2+ with nitrite in acid or neutral (pH 7.4) solution. The similar results obtained in both ways indicate that the aqua complex was able to convert nitrite into coordinated nitrosyl. The reactivity of [Si(CH2)3(isn)Ru(NH3)4(NO)]3+ was investigated in order to evaluate the nitric oxide (NO) release. It was found that, upon light irradiation or chemical reduction, the immobilized nitrosyl complex was able to release NO, generating the corresponding Ru(III) or Ru(II) aqua complexes, respectively. The NO material could be regenerated from these NO-depleted materials obtained photochemically or by reduction. Regeneration was done by reaction with nitrite in aqueous solution (pH 7.4). Reduction–regeneration cycles were performed up to three times with no significant leaching of the ruthenium complex.[Si(CH2)3(isn)Ru(NH3)4(NO)]3+ releases NO photochemically or by chemical reduction. Regeneration of the material cyclic conversions of nitrite to NO occurs by reaction of the reduced material with nitrite.
Keywords: Nitric oxide; Nitrite; Conversion; Silica gel; Ruthenium; Nitrosyl; Controlled; Photochemistry; Tetraammine; Aminopropylsilica; Functionalized silica; Nitric oxide donor;

The effect of particle size on the reactivity of hexyltrimethoxysilane (C6S) with the particle surface was studied by using silica nanoparticles (SNPs) with different diameters (30 or 200 nm). In case of 30-nm SNPs, a large amount of isolated silanol was observed. On the other hand, in the case of 200-nm SNPs, the amount of hydrogen bonded silanol and hydrogen bonded water molecules at the surface of the SNPs increased. Since the hydrogen bonded silanol and the hydrogen bonded water enhanced the reaction of C6S with SNPs, the chemisorbed C6S on 200-nm SNPs was larger than that on 30-nm SNPs. Furthermore, the effects of surface modification on the dispersion stability in MEK were studied using viscosity measurements and surface force measurements by the AFM colloid probe method. The viscosity of the dilute SNPs/MEK suspension did not change by the chemisorptions of C6S; however, the viscosity of dense suspension reduced effectively by surface modification. It was estimated that the suspension viscosity reduced effectively when the mean particle surface distance in the suspension was near to the distance where the repulsive force appeared by the surface force measurements using the colloid probe AFM.Silica particle size had an effect on the reactivity of hexyltrimethoxysilane with silica particle surface.
Keywords: Silica; Methylethylketone; Hexyltrimethoxysilane; AFM colloid probe; Silanol; Viscosity; Particle size effect;

Nonlinear friction characteristics between silica surfaces in high pH solution by Elena Taran; Yoichi Kanda; Ivan U. Vakarelski; Ko Higashitani (425-432).
Molecular-scale characteristics of friction forces between silica particles and silica wafers in aqueous solutions of the normal (pH 5.6) and high pH (pH 10.6) are investigated, using the lateral force measuring procedure of the atomic force microscope (AFM). Various significant differences of friction characteristics between solutions of normal and high pH's are found. In the case of solutions of normal pH, the friction force increases linearly with increasing loading force, as the Amonton's law for solid bodies indicates. However, in the case of high pH solutions, the increasing rate with the loading force is considerably reduced in the low loading region, but the value increases abruptly above a critical loading force to overcome the magnitude of friction force of normal pH above the region of very high loading. It is very interesting to know that this nonlinear force curve at high pH is independent of the atomic-scale roughness of surfaces, although the magnitude of friction is greatly influenced by the roughness in the case of normal pH. The reason why the friction at high pH is independent of the surface roughness is postulated to be due to the hairy-like layer formed on the silica surface. The existence of hairy-like layers at high pH is proven directly by the dynamic method of normal force measurements with AFM and the thickness is estimated to be at least ca. 1.3 nm.
Keywords: Friction; Hairy layer; Lubrication; Silica surface; CMP; High pH;

Population balance modeling of aggregation and breakage in turbulent Taylor–Couette flow by M. Soos; L. Wang; R.O. Fox; J. Sefcik; M. Morbidelli (433-446).
An experimental and computational study of aggregation and breakage processes for fully destabilized polystyrene latex particles under turbulent-flow conditions in a Taylor–Couette apparatus is presented. To monitor the aggregation and breakage processes, an in situ optical imaging technique was used. Consequently, a computational study using a population balance model was carried out to test the various parameters in the aggregation and breakage models. Very good agreement was found between the time evolution of the cluster size distribution (CSD) calculated with the model and that obtained from experiment. In order to correctly model the left-hand side of the CSD (small clusters), it was necessary to use a highly unsymmetric fragment-distribution function for breakage. As another test of the model, measurements with different solid volume fractions were performed. Within the range of the solid volume fractions considered here, the steady-state CSD was not significantly affected. In order to correctly capture the right-hand side of the CSD (large aggregates) at the higher solid volume fraction, a modified aggregation rate prefactor was used in the population balance model.An experimental and computational study of aggregation and breakage processes for fully destabilized polystyrene latex particles under turbulent-flow conditions in a Taylor–Couette apparatus is presented.
Keywords: Aggregation; Breakage; Cluster size distribution; Image analysis; Population balance equation; Polystyrene microsphere; Taylor–Couette flow;

Reported here is the study on the structure of Langmuir–Blodgett (LB) films of double-armed dibenzo-18-crown-6 contain biphenyl (DACE) which are newly synthesized and mixed with stearic acid (SA). In addition, the miscibility of the two compounds was also tested by the measurement of the surface pressure–area ( π – A ) isotherms of DACE and DACE/SA with various proportions. It is noted that there is no phase segregation in the mixed monolayer film of DACE/SA. Upon calculation of the excess surface area, it is concluded that the SA molecule can enter into the crown ether ring, while an 18C6 ring can host a maximum of one SA molecule. The difference of spectroscopic properties of DACE in LB films and bulk solution has been investigated by ultraviolet–visible (UV–vis) and Fourier-transfer infrared (FTIR) measurements. Molecules of DACE exist in the mixed LB films as monomers in contrast to those in the concentrated solution as aggregates. The hydrocarbon chains in DACE and DACE/SA LB films are tilted to the normal of the substrate surface, but perpendicular to the dipole moment of C=O. Both C―O bonds in the phenyl ethers and carboxylic ester of DACE, and the long axes of phenyl rings are aligned nearly perpendicular to the substrate surface. Infrared spectra of mixed LB films of DACE/SA present further evidence that the SA molecules enter into the crown ether rings of DACE.The structure of Langmuir–Blodgett films of DACE mixed with SA was studied. The amount of SA molecules located within crown ether rings increases with the molar ratio of SA.
Keywords: Crown ethers; Spectroscopy; Structure; Miscibility; Orientation;

Structural studies of the phase, aggregation and surface behaviour of 1-alkyl-3-methylimidazolium halide + water mixtures by Ian Goodchild; Laura Collier; Sarah L. Millar; Ivan Prokeš; Jason C.D. Lord; Craig P. Butts; James Bowers; John R.P. Webster; Richard K. Heenan (455-468).
The surface, phase and aggregation behaviour of mixtures of 1-alkyl-3-methylimidazolium halide, [C n mim]X, where n is the alkyl chain length, with water has been explored using a variety of methods. Critical micelle concentrations (cmc) and micelle structures have been determined for aqueous [C n mim]Br solutions for n = 2 , 4, 6, 8, and 10. Small-angle neutron scattering (SANS) measurements reveal that for the n = 8 and 10 systems, at concentrations just above the cmc, small near-spherical aggregates exist, which, after initial growth, possess core radii (aggregation numbers) at intermediate concentrations of 10.5 ± 0.5 Å ( 22 ± 2 ) and 13.2 ± 0.5 Å ( 40 ± 3 ), respectively, for n = 8 and n = 10 . Towards higher concentrations, the aggregates appear to grow, with the aggregates in the [C10mim]Br system becoming increasingly elongated (prolate) with increasing concentration. No evident aggregates are formed in the systems with n = 2 and 4. In the n = 6 system, it appears that oblate aggregates with radius ∼9 Å form at the cmc and that the radius increases with increasing concentration. For longer alkyl chain lengths, at high concentrations lyotropic mesophases form in some systems. The mesophase region for the [C8mim]Cl system has been explored across the composition range using X-ray diffraction and 2H NMR spectroscopy. Both techniques suggest that a major hexagonal phase with lattice parameter of 29.5 ± 0.5 Å coexists with a minor lamellar phase ( 23.5 ± 0.3 Å ) or possibly a second hexagonal phase ( 27.1 ± 0.4 Å ) . The area per adsorbed molecule at the surface of [C8mim]Br solutions has been measured as a function of concentration using neutron reflectometry. A minimum in the area per molecule behaviour is coincident with a minimum identified in the surface tension isotherm occurring close to the cmc. The data suggest depletion of [C8mim]Br from the surface region occurs at concentrations immediately above the cmc.Mixtures of 1-alkyl-3-methylimidazolium halide in water show interesting surface, phase and aggregation behaviour on variation of the alkyl chain length.

Turbidimetric study of fluorite nucleation in solution by Hans E. Lundager Madsen (469-476).
Precipitation of fluorite (calcium fluoride) from solution at 30 and 37 °C has been studied by measurement of turbidity at different wavelengths, analyzing the data with the aid of the Mie theory of light scattering from small particles. In this way both number density and average particle size were obtained as functions of time. The values were confirmed by sedimentation analysis. In the later part of the process the results were strongly influenced by agglomeration and sedimentation, but the initial part of the curve of number density vs time was useful in determination of nucleation kinetics. The trend of nucleation frequency vs supersaturation agreed well with the classical theory of Becker, Döring, Volmer, Zel'dovich, and Frenkel, and surface energies equal to 102   mJ / m 2 at 30 °C and 89   mJ / m 2 at 37 °C were found. On the other hand, the absolute rate of nucleation was many orders of magnitude lower than that predicted by the theory, which is ascribed to an overestimate of the rate of growth of postcritical nuclei.
Keywords: Nucleation; Surface energy; Turbidimetry; Mie theory; Calcium fluoride; Fluorite;

A method for the evaluation of quantities that are experimentally inaccessible such as the surface tension at the solid–vacuum interface and the superficial tension of the fluid in contact with the solid is presented. The approach is based on consideration of an equilibrium of a fluid in solid capillary wherein a balance between surface and capillary forces has been replaced by conceptual alternative interfacial and centrifugal forces. This approach involves the simultaneous numerical solution one the special forms of the Gibbs equation for solid–fluid interface and a generalized Kelvin equation derived earlier. The latter equation takes into account interactions between the solid thick cylindrical wall and confined fluid, this body–body interaction potential has been primarily calculated using the Lennard-Jones (6-12) expression for the atom–atom pair potentials and expressed by hypergeometrical functions having good convergences. All numerical calculations shown here have been performed for the model graphite–argon system at 90 K. Finally, an analysis of the accuracy of the proposed method is considered.In concept, the liquid hollow cylinder can rotate about its longitudinal axis at some constant angular velocity such that the centrifugal force due to rotary motion is able to exactly compensate the fluid surface forces cancelling them out. In this instance, the kinetic energy of rotary motion plays a role, which is equivalent to that played by the wall potential of the solid capillary.
Keywords: Surface tension of solids; Superficial tension; Body–body potential; Generalized Kelvin equation; Graphite;

Methylated and hydroxypropylated cyclodextrins (CDs) are highly efficient mass transfer promoters in biphasic aqueous organometallic processes. The surface tension measurements demonstrated that these CDs adsorb at air–water interface and allowed to determine surface excess of CD by using Gibbs adsorption equation. Interestingly, a good correlation between surface excess and catalytic activity was obtained in the case of hydroformylation and Tsuji–Trost reactions. These results point out the importance of CD adsorption at the interface in biphasic aqueous organometallic processes.Surface tension data demonstrated the importance of CD adsorption at the interface during biphasic aqueous organometallic processes.
Keywords: Modified cyclodextrins; Hydroformylation; Tsuji–Trost; Adsorption; Surface excess; Surface tension; Molecular area;

The influence of L-tryptophan (L-Trp) on the interphase electric properties of sodium dodecyl sulfate (SDS)/n-pentanol (n-C5H11OH)/water (H2O) system was studied by the method of AC impedance, and the distribution of L-Trp between the microemulsion phases with different structures in SDS/n-C5H11OH/H2O system was determined by UV–vis spectroscopy. The results show that L-Trp transfers from the lower phase (O/W or bicontinuous) to the upper phase (W/O), and that a small amount of SDS transfers from the upper phase to the lower phase correspondingly with the increase of the total SDS content at a constant weight ratio of n-C5H11OH/H2O = 50/50 and a total L-Trp concentration of 1.0 × 10 −4   mol / L . In addition, the concentrations of L-Trp in both the upper and lower phases increase, but the SDS content decreases slightly in the upper phase and increases appreciably in the lower phase with the increase of the total L-Trp concentration at a constant total content of SDS. The interphase capacitance and the interphase charge-transfer current of the system increase, but the interphase resistivity decreases.
Keywords: SDS; Microemulsion; L-tryptophan; Capacitance; Charge-transfer current;

Evaporation from an ionic liquid emulsion by Stig E. Friberg (494-499).
The conditions during evaporation in a liquid crystal-in-ionic liquid microemulsion (LC/μEm) were estimated using the phase diagram of the system. The equations for selected tie lines were established and the coordinates calculated for the sites, at which the evaporation lines crossed the tie lines. These values combined with the coordinates for the phases connecting the tie lines were used to calculate the amounts and the composition of the fractions of the two phases present in the emulsion during the evaporation. One of the emulsion phases was a lamellar liquid crystal and high energy emulsification would lead to the liquid crystal being disrupted to form vesicles. Such a system tenders a unique opportunity to study the interaction between vesicles and normal micelles, which gradually change to inverse micelles over bi-continuous structures. The amount of vesicles in the liquid phase versus the fraction liquid crystal was calculated for two extreme cases of vesicle core size and shell thickness. The limit of evaporation while retaining the vesicle structure was calculated for emulsions of different original compositions assuming the minimum continuous liquid phase to be 50% of the emulsion.
Keywords: Emulsions; Microemulsions; Vesicles; Evaporation; Detergents; Amphiphiles;

Ultrasonic velocity measurements as a method for investigating phase transitions of monoglyceride emulsifier systems in pearlescent cosmetic creams by Cécile Alberola; Thomas Dederichs; Detlef Emeis; Martin Möller; Tobias Sokolowski; Klaus-Peter Wittern (500-508).
The phase transitions of monoglyceride emulsifier systems and pearlescent effects in cosmetic creams are investigated using ultrasonic velocity measurements. The transitions between the different phases of monoglyceride emulsifier systems—the coagel, liquid–crystalline lamellar phase, and gel phase—are detected in creams by changes in the ultrasonic velocity with variation of the temperature. The phase transition temperatures correspond to DSC results. Furthermore, the slope of the ultrasound velocity curve correlates with the amount of bound water in the different phases. These insights into the ultrasonic velocity properties of the monoglyceride emulsifier system of creams make it possible to more closely study the pearlescent effect of the coagel. The temperature domain of the short time reversibility of the pearlescence as well as the back-formation time of the coagel can be determined with this method, which enable the optimization of the formulation of pearlescent creams.
Keywords: Ultrasonic velocity; Phase transition; Monoglyceride; Coagel; Gel phase; Liquid–crystalline lamellar phase; Pearlescence; Cosmetic cream;

Rheology of double emulsions by Rajinder Pal (509-515).
New equations for the viscosity of concentrated double emulsions of core–shell droplets are developed using a differential scheme. The equations developed in the paper predict the relative viscosity ( η r ) of double emulsions to be a function of five variables: a / b (ratio of core drop radius to shell outer radius), λ 21 (ratio of shell liquid viscosity to external continuous phase viscosity), λ 32 (ratio of core liquid viscosity to shell liquid viscosity), ϕ DE (volume fraction of core–shell droplets in double emulsion), and ϕ m DE (the maximum packing volume fraction of un-deformed core–shell droplets in double emulsion). Two sets of experimental data are obtained on the rheology of O/W/O (oil-in-water-in-oil) double emulsions. The data are compared with the predictions of the proposed equations. The proposed equations describe the experimental viscosity data of double emulsions reasonably well.
Keywords: Emulsion; Multiple emulsion; Double emulsion; Rheology; Viscosity;

Ionic separation efficiency of a novel electric-field-assisted membrane module comprising an array of microchannel units by Jyh-Ping Hsu; Sung-Hwa Lin; Shiojenn Tseng; Ay Su; Duu-Jong Lee; Chur-Jen Chen (516-523).
The ionic separation efficiency of a novel membrane module comprising an array of microchannel units is analyzed. Under the Debye–Hückel approximation, we derive a semianalytical expression for the ionic separation efficiency. Analyses reveal that the effects of the size of the microchannel, the fixed charge density in the membrane layer, and the permittivity of the membrane layer on ionic separation efficiency depend strongly on the valence type of electrolyte in treated water. Under the condition of a symmetric electrolyte, the ionic separation efficiency is found to be about unity and unresponsive to variation of system parameters. If the valence of the cation is higher than that of the anion, the ionic separation efficiency is larger than unity, and decreases to unity as the size of the microchannel increases. In contrast, if the valence of the cation is lower than that of the anion, the ionic separation efficiency is smaller than unity and increases to unity as the size of the microchannel increases. Under the latter two conditions, the effects of both fixed charge density in the membrane layer and permittivity of the membrane layer on the ionic separation efficiency are found to be reversed.Schematic representation of a microchannel unit. A microchannel unit is a combination of an inner microchannel and an outer charged surface membrane aligned axially and concentrically.
Keywords: Microchannel unit; Charged membrane layer; Ionic separation efficiency; Debye–Hückel approximation; Valence type of electrolyte;

SiO2–TiO2 pillared layered manganese oxide nanohybrid was successfully synthesized by preliminarily expanding the interlayer of H-type layered manganese oxide using dodecylamine, followed by reacting it with a mixture solution of titanium isopropoxide and tetraethylorthosilicate. The basal spacing and the pillared agent content of the obtained materials connected with the length of intercalated n-alkylamine, incorporated Si/Ti molar ratios and the solvothermal treatment temperature. The structural evolution of SiO2–TiO2 pillared layered manganese oxide nanohybrid was characterized by XRD, DSC-TGA, SEM, IR, N2 adsorption–desorption and element analyses. TiO2 particles exhibited a stronger affinity for the negatively charged manganese layers, and the TiO2 particles incorporated were independently intercalated without any distinct chemical bonding with the co-intercalated SiO2 particles. SiO2–TiO2 pillared layered manganese oxide nanohybrid had a BET surface area of 98 m2/g with a gallery height of about 1.43 nm between layers. The obtained SiO2–TiO2 co-pillared layered manganese oxide nanohybrid is expected as a selective catalyst, or an improved battery material.
Keywords: Layered manganese oxide nanohybrid; Pillar; Solvothermal treatment; Titanium dioxide; Silicon dioxide;

The enthalpy produced during immersion in water of a smectite, identified as a montmorillonite, substituted by Ca or Na is analyzed using three different approaches. The heat of immersion is measured using the classical calorimetric method. It is compared to an estimate using adsorption techniques. And it is calculated from a theoretical estimate of the surface energy of a crystal model of montmorillonite. The comparison of the different values allows the enthalpy linked to the swelling phenomenon to be estimated. The Ca form appears in every case to interact more strongly with water molecules than the Na form.The solid surface tensions of Na-montmorillonite and Ca-montmorillonite from an Algerian deposite are computed in order to interpret data on heat of immersion in water. The immersion heat contains adsorption, spreading, and swelling terms. Analysis of results is in agreement with a quantitative analysis of adsorption isotherms.
Keywords: Montmorillonite; Calcium; Sodium; Swelling; Cation hydration; Surface energy; Adsorption; Immersion;

Self-aggregation of mixed binary nonionic and ionic surfactants comprising N-methyl-N-decanoyl glucamide (MEGA 10) and alkyltrimethylammonium bromides (C12-, C14-, and C16TAB) has been investigated in detail by different physical methods. The counter-ion binding, aggregation number, and polarity of the mixed micelles have been determined. The results have been analyzed in the light of the theories of Rubingh and Maeda. The thermodynamic parameters of the micellization process have been evaluated and discussed. The interfacial adsorptions of the mixed amphiphiles including their surface excesses and head-group areas have also been evaluated. Based on the head-group areas, the overall shapes of the mixed micelles have been predicted from the estimation of the amphiphile packing parameters.
Keywords: MEGA 10; Alkyltrimethylammonium bromides; Mixed micelles; Aggregation; Counter-ion binding; Energetics; Adsorption; Monomer packing;

Citrate-assisted synthesis of prickly nickel microwires and their surface modification with silver by Xiaomin Ni; Junhao Zhang; Yongfeng Zhang; Huagui Zheng (554-558).
A new type of prickly nickel microwires assembled by thornlike nanocrystals was fabricated through a simple chemical reduction route with the assistance of citrate. Thus-prepared nickel wires were subsequently morphology-retained modified with a thin silver shell via transmetallation. Compared with the uncoated sample, the Nicore–Agshell wires exhibited much-enhanced oxidation resistance, slightly changed magnetic properties and stark different catalysis for the creation of carbon particles in pyrolyzing acetone.A new type of prickly Nicore–Agshell wires assembled by thornlike nanocrystals was fabricated through transmetallation reaction of nickel wires with Ag+ ions. Compared with the pure nickel sample, the Nicore–Agshell wires exhibited much-enhanced oxidation resistance, slightly changed magnetic properties and stark different catalysis for the creation of carbon particles in pyrolyzing acetone.
Keywords: Nickel; Magnetic measurements; Catalysis; Carbon;

Synthesis of stable luminescent microspheres by a simple method by Qiaoling Liu; Xuanming Liu; Yonghua Zhu; Dongying Tang (563-566).
An easy procedure for preparing microspheres containing CdSe/CdS core–shell quantum dots (QDs) was demonstrated. The luminescent properties of this microsphere were characterized by fluorescence microscopy and fluorescence spectrophotometry. Scanning electron microscopy was also used in this study. Laser confocal microscopy was carried out to describe the distribution of QDs in the microsphere. Especially, the stability of microspheres was investigated. It was found that the getting microsphere was very stable in water and showed values for physiological conditions. The inherent stability of the spheres, as well as their photostability, allows them to be used in biological applications.A simple method of preparing luminescent microspheres was demonstrated. These microspheres were very stable under physiological conditions and can keep their bright fluorescence for 2 weeks.
Keywords: Microsphere; Quantum dots; CdSe/CdS; Polylysine; Fluorescence;

Preparation of CeO2–ZrO2 ceramic fibers by electrospinning by Yanfei Zhang; Jiayan Li; Qin Li; Ling Zhu; Xiangdong Liu; Xinghua Zhong; Jian Meng; Xueqiang Cao (567-571).
Electrospinning was employed to fabricate polymer–ceramic composite fibers from solutions containing poly(vinyl pyrrolidone) (PVP), Ce(NO3)3⋅6H2O and ZrOCl2⋅8H2O. Upon firing the composite fibers at 1000 °C, Ce0.67Zr0.33O2 fibers with diameters ranging from 0.4 to 2 μm were synthesized. These fibers exhibit strong resistance to sintering. They still have specific surface area around 11.8 m2/g after being heated at 1000 °C for 6 h.Figure shows that these Ce0.67Zr0.33O2 ceramic fibers calcined at 1000 °C are a mixture of dense and hollow fibers with a diameter of 0.4–2 μm.
Keywords: Catalytic combustion; CeO2–ZrO2 solid solutions; Electrospinning; Ceramic fibers; Thermal sintering;

Effect of ionic surfactants on bauxite residues suspensions viscosity by M. Clifton; T. Nguyen; Ray Frost (572-577).
Measurement of the rheological property of bauxite residue sample received from an Australian alumina refinery, treated with a number of cationic and anionic surfactant in laboratory has been carried out using a Brookfield viscometer for the assessment of the effect of surfactants on the residue viscosity. Sodium laurate, prepared with an excess of sodium hydroxide, was found to be effective while direct addition of anionic surfactants (lauric acid and sodium laureth sulphate) and cationic (cetyl trimethyl ammonium bromide) produce only moderate effect on the red mud suspension apparent viscosity at 65 °C. The experimental data appear to confirm the crucial role of the cation sodium in the process of adsorption of anionic surfactants on the flocculated red mud particles.Alteration of bauxite residue suspensions viscosity can be achieved with the use of suitable surfactant. The crucial role of the cation sodium in the process of surfactant adsorption onto the particle surface is recognised as shown in the figure.
Keywords: Red mud; Bauxite residues; Rheology; Surfactant; Viscosity reduction;

Phase behavior of aqueous mixture of imidazolium ionic liquid, 1-dodecyl-3-methylimidazolium bromide, was investigated by means of differential scanning calorimetry and polarized optical microscopy. The mixture forms two types of lyotropic liquid-crystalline gels, one is composed of lamellar phase and the other is of hexagonal phase. T – X phase diagram of the mixture was constructed, which defines the regions of various phases appearing in this mixture.Aqueous mixture of long-chained imidazolium ionic liquids forms lyotropic liquid-crystalline gel depending on the composition. The phase diagram of this system was constructed on the basis of DSC measurements and POM observation.
Keywords: Long-chained imidazolium ionic liquid; Aqueous mixture of ionic liquid; Phase behavior; Lyotropic liquid-crystalline gel; Phase diagram; Differential scanning calorimetry;

by Arthur Hubbard (582).