Journal of Colloid And Interface Science (v.291, #1)



In the past few years, measurements of the pair interaction potential have shown evidence of micrometer-range attractive interactions between colloidal particles trapped between glass plates. In these experiments it is believed that the glass walls play an important role in the observed attractions. Colloidal particles trapped at the air/water interface show the formation of different 2-D colloidal patterns such as foams, clusters, and chains, whose formation has been taken as evidence of micrometer-range attractive interaction. Here, we present measurements of the pair interaction potential between 0.5-μm colloidal particles at the air/water interface. Indeed, the pair potential shows an attractive secondary minimum at about 1.9σ, where σ is the particle's diameter. Surprisingly, the position and depth of the secondary well are similar to those found in colloidal systems trapped between glass plates. However, we do not have a clear explanation on the origin of the attractive component of the interaction potential. Attractive colloidal interactions at the air/water interface.Display Omitted
Keywords: Colloidal interactions; Air/water interface; Like-charge attractions;

Hollow carbonaceous capsules from glucose solution by Xiaoming Sun; Yadong Li (7-12).
An easy hydrothermal method was developed for preparing hollow carbonaceous capsules with reactive surface layer and tunable void size, and shell thickness through a hydrothermal method at 180 °C, using only the anionic surfactant sodium dodecyl sulfate (SDS) and glucose as starting material. Ag nanoparticles of less than 10 nm were loaded onto the surface of capsules under ambient condition. Products were characterized with TEM, SEM, and FT-IR spectra. The process is green, cheap, and easy. Since no toxic materials were used in preparation and as-prepared capsules a shared reactive surface layer and a stable carbonaceous framework, the capsules might find application in fields such as biochemistry, pharmaceutics, and clinical diagnostics. A facile hydrothermal method was developed using anionic surfactant (SDS) as soft templates and glucose as starting material to hollow carbon capsules with polysaccharide-like surface.Display Omitted
Keywords: Carbonaceous materials; Capsules; Hollow structures; Biochemistry; Drug delivery; SDS; Glucose;

Exfoliated polystyrene (PS)/ZnAl layered double hydroxide (LDH) nanocomposites have been synthesized via emulsion polymerization in the presence of N-lauroyl-glutamate surfactants and long-chain n-hexadecane. The samples were characterized using elemental analysis, Fourier transform infrared (FTIR) spectrum, X-ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The XRD and TEM results demonstrate that the exfoliated ZnAl–LDH layers of 50–70 nm width and about 1 nm thickness were well dispersed at molecular level in the PS matrix. And the completely exfoliated PS/LDH nanocomposites can be obtained even at the 10 wt% LDH loading. When the 50% weight loss was selected as a comparison point, the decomposition temperature of exfoliated PS/LDH sample with 5 wt% LDH was ca. 28 °C higher than that of pure PS.
Keywords: Nanostructure; Polymer/layered double hydroxide (LDH) nanocomposites; Emulsion polymerization; Thermal properties;

The sorption of basic dyes (methylene blue, malachite green, rhodamine B, crystal violet) onto a nonconventional organomineral sorbent—iron humate—was examined in the presence of various kinds of surfactants. It was found that nonionic (Triton X-100) and cationic (cetyltrimethylammonium bromide) surfactants exhibited a relatively small effect on the dye sorption. Anionic surfactants (sodium dodecyl sulfate), on the other hand, affected (in most cases) dramatically the sorption of basic (cationic) dyes. Typically, the dye sorption was enhanced in the presence of low concentrations of anionic surfactants. At high surfactant concentrations, a steep decrease in the dye sorption was observed in some systems, probably due to the formation of micelles that solubilize the dye molecules and prevent their sorption. A model describing these experimental dependencies was proposed. The sorption of basic dyes onto iron humate may be described by the pseudo-second-order kinetic equation. Diffusion processes were identified as the main mechanisms controlling the rate of the dye sorption.
Keywords: Adsorption isotherms; Adsorption kinetics; Basic dyes; Surfactants; Humic substances;

This paper reports an analysis of the irreversible deposition of colloidal particles from the pressure-driven flow in a microchannel within the framework of DLVO theory. A theoretical model is presented on the basis of the stochastic Langevin equation, incorporating the random Brownian motion of colloidal particles. Brownian dynamics simulation is used to compute the particle deposition in terms of the surface coverage. To validate the theoretical model, experiments are carried out using the parallel-plate flow cell technique, enabling direct videomicroscopic observation of the deposition kinetics of polystyrene latex particles in NaCl electrolytes. The theoretical predictions are compared with the experimental results, and good agreement is found. Particle deposition experiments were carried out using the parallel-plate flow cell technique with a video microscope under dark-filed illumination. A model based on Brownian dynamics simulation was developed.Display Omitted
Keywords: Colloidal particle deposition; Brownian dynamics simulation; Langevin equation; Parallel-plate flow; Blocking effect;

Interactions between C.I. Basic Blue 41 and aluminosilicate sorbents by Maria Roulia; Alexandros A. Vassiliadis (37-44).
Four aluminosilicate sorbents (montmorillonite, bentonite, raw perlite, and expanded perlite) were employed for retention of the cationic dye C.I. Basic Blue 41. Interactions between the clay and the dyestuff were investigated at several temperatures and clay:dye ratios. The mechanism behind the adsorption involves the formation of H-aggregates of the dye on both clays, followed by dye migration into the interlayer in the case of montmorillonite. Time-dependent absorbance spectra revealed the presence of various dye species in montmorillonite. Introduction of the dye molecules into the interlamellar space occurs more rapidly in bentonite than in montmorillonite. The dye molecules inserted between the clay leaves adopt different orientations and, eventually, stack in layers at increased dye loadings for both montmorillonite and bentonite. Higher dye aggregates are then present as suggested by diffuse reflectance spectroscopy. Dye sorption on both raw and expanded perlite proceeds via H-aggregate formation as well.
Keywords: Perlite; Clays; Montmorillonite; Bentonite; Adsorption; Dyes; C.I. Basic Blue 41;

Dialkyldimethylammonium films on mica prepared via ion exchange from solution have been reported to be of high quality in terms of their density and molecular orientation. Different preparation procedures are described in the literature. The molecular order and the inclination of the alkyl chains, however, are often deduced from indirect experimental evidence such as the wettability and the film thickness. In the present study we employed near edge X-ray absorption fine structure spectroscopy (NEXAFS) to determine directly the order of the molecules adsorbed from different solvents (water, methanol, water/methanol 1:1, cyclohexanol, and chloroform). It was found that films prepared from different solvents are displaying large differences in the established surface coverage and orientation. In particular, NEXAFS disclosed that the orientation of the alkyl chains can differ significantly even when similar water contact angle values are observed.
Keywords: Ion-exchanged films; Mica; Surfactants; Dialkyldimethylammonium ions; Solvent; Molecular orientation; NEXAFS;

A method for the attachment of ammonia to modified silica gel has been developed. In the first step, tetraethylorthosilicate and (3-glycidoxypropyl)trimethoxysilane were co-condensed in the presence of n-dodecylamine, a neutral surfactant template, to produce a modified mesoporous silica. The epoxy group incorporated into the mesoporous silica was opened by ammonia gas thus introducing amine chelate groups covalently bound to the inorganic surface. The modified material contained 1.13 ± 0.06 mmol of amine per gram of silica, exhibited a surface area of 831 ± 29   m 2 g −1 and a porous diameter of 1.95 nm. Infrared, 29Si and 13C NMR spectra were in agreement with the proposed structure of the modified mesoporous silica in the solid state. This ordered organic–inorganic hybrid presented a high capacity for the removal of the agrochemical 2,4-dichlorophenoxyacetic acid from water: the ΔH and ΔG values for the interaction were determined to be −110.61 and −9.37 kJ mol−1, respectively.
Keywords: Silica; 2,4-Dichlorophenoxyacetic acid; Adsorption; Calorimetric analysis;

Losses of surfactants through sorption to soils/sediments, especially to clay minerals, by various chemical interactions such as sorption and precipitation threaten the success of surfactant in enhancing remediation of contaminated soil and groundwater. In this study, the behavior of mixtures of a nonionic surfactant (TX-100) and an anionic surfactant (SDBS) sorbed to a montmorillonite saturated with calcium (Ca-montmorillonite) was investigated, and compared with that of individual surfactants. It is shown that the amounts of both TX-100 and SDBS sorbed to Ca-montmorillonite are significant. However, the amount of either TX-100 or SDBS sorbed can be decreased and minimized when they are mixed with each other. Mixed micelle formation, which causes negative deviation of critical micelle concentrations (CMCs) from the ideal, is responsible for the decrease in sorbed TX-100 and sorbed SDBS in their mixtures. Because of their ability to minimize their amounts sorbed and thus enhance their active concentrations, as observed in mixed TX-100 and SDBS systems, mixed anionic–nonionic surfactants exhibit potential advantages in the area of enhanced soil and groundwater remediation.
Keywords: Mixed surfactants; Surfactant-enhanced remediation; Sorption; Precipitation; Montmorillonite;

Adsorption of fluoride, chloride, bromide, and bromate ions on a novel ion exchanger by N.I. Chubar; V.F. Samanidou; V.S. Kouts; G.G. Gallios; V.A. Kanibolotsky; V.V. Strelko; I.Z. Zhuravlev (67-74).
A novel ion exchanger based on double hydrous oxide (Fe2O3⋅Al2O3xH2O) was obtained by the original sol–gel method from easily available and cheap raw materials and employed for adsorption of F, Cl, Br, and BrO 3 from simultaneous solutions. Adsorbent was characterized by potentiometric titration, ζ-potential, and poremetrical characteristics. A technologically attractive pH effect of F, Br, and BrO 3 sorption on the investigated double hydroxide of Fe and Al, which is capable of working in the pH range 3 to 8.5, was observed. Kinetic data on fluoride and bromide sorption fit well the pseudo-second-order model. Isotherms of fluoride, bromide, chlorine, and bromate ion sorption on Fe2O3⋅Al2O3xH2O were obtained at pH 4. The isotherm of F sorption fit well the Langmuir model; sorption affinity ( K = 0.52  L / mg ) and sorption capacity (90 mg F / g) were high. In the competitive adsorption of bromide and bromate, bromide dominated at equilibrium concentrations of the ions >40 mg / L. The mechanism of fluoride adsorption to the surface of the model cluster of the sorbent synthesized and the geometry of the cluster itself were modeled with the HyperChem7 program using the PM3 method. The novel ion exchanger based on mixed hydrous oxide for halides removal from water solutions at different pHs (model cluster obtained with quantum-chemistry program HyperChem7).Display Omitted
Keywords: Inorganic ion exchangers; Adsorption; Anions; Isotherms; Quantum chemistry modeling;

Carboxymethyl cellulose (CMC) is a polysaccharide which is widely used in many industrial sectors including food, textiles, paper, adhesives, paints, pharmaceutics, cosmetics and mineral processing. It is a natural organic polymer that is non-toxic and biodegradable. These properties make it ideal for industrial applications. However, a general lack of understanding of the interaction mechanism between the polysaccharides and solid surfaces has hindered the application of this polymer. In this work, adsorption of CMC at the solid–liquid interface is investigated using adsorption and electrophoretic mobility measurements, FTIR, fluorescence spectroscopy, AFM and molecular modeling. CMC adsorption on talc was found to be affected significantly by changes in solution conditions such as pH and ionic strength, which indicates the important role of electrostatic force in adsorption. The pH effect on adsorption was further proven by AFM imaging. Electrokinetic studies showed that the adsorption of CMC on talc changed its isoelectric point. Further, molecular modeling suggests a helical structure of CMC in solution while it is found to adsorb flat on the solid surface to allow its OH groups to be in contact with the surface. Fluorescence spectroscopy studies conducted to investigate the role of hydrophobic bonding using pyrene probe showed no evidence of the formation of hydrophobic domains at talc–aqueous interface. Urea, a hydrogen bond breaker, markedly reduced the adsorption of CMC on talc, supports hydrogen bonding as an important factor. In FTIR study, the changes to the infrared bands, associated with the C―O stretch coupled to the C―C stretch and O―H deformation, were significant and this further supports the strong hydrogen bonding of CMC to the solid surface. In addition, Langmuir modeling of the adsorption isotherm suggests hydrogen bonding to be a dominant force for polysaccharide adsorption since the adsorption free energy of this polymer was close to that for hydrogen bond formation. All of the above results suggest that the main driving forces for CMC adsorption on talc are a combination of electrostatic interaction and hydrogen bonding rather than hydrophobic force. The objective of this study was to clarify the mechanistic aspects of the interactions between CMC and talc using a combination of spectroscopic, microscopic, molecular modeling.Display Omitted
Keywords: Talc; CMC; Polymer adsorption; Fluorescence; AFM; Model; Zeta potential; FTIR;

Enrichment of Pb(II) ions using phthalic acid functionalized XAD-16 resin as a sorbent by Saima Q. Memon; S.M. Hasany; M.I. Bhanger; M.Y. Khuhawar (84-91).
A simple and reliable method has been developed using polymeric material containing phthalic acid as a chelating agent to concentrate ultratrace amounts of lead ions in aqueous solutions. After characterization by CHN, IR, and thermal studies, the static and dynamic sorption behavior of Pb(II) ions onto new synthetic resin has been investigated. The sorption has been optimized with respect to pH, shaking speed, and contact time between the two phases. Maximum sorption is achieved from solution of pH 5–8 after 10 min agitation time. The lowest concentration for quantitative recovery is 5.8 ng cm−3 with a preconcentration factor of ∼850. The kinetics of sorption follows the first-order rate equation with the rate constant k = 0.58 ± 0.04   min −1 . The variation of the equilibrium constant K c with temperature between 10 and 50 °C yields values of ΔH, 52.4 ± 1.65   kJ mol −1 , ΔS, 186 ± 5.21   J mol −1 K −1 , and Δ G 303 K , − 4.15 ± 0.002   kJ mol −1 . The sorption data of Pb(II) ions in the concentration range from 2.41 × 10 −6 to 1.44 × 10 −4   mol L −1 follows the Langmuir, Freundlich, and Dubinin–Radushkevich (D–R) isotherms at all temperatures investigated. The sorption of Pb(II) ions onto synthesized resin in the presence of common anions and cations has also been measured. The possible sorption mechanism of Pb(II) ions onto phthalic acid modified XAD-16 is also discussed. The sorption procedure is utilized to preconcentrate Pb(II) ions prior to their determination in automobile exhaust particulates by atomic absorption spectrometry using direct and standard addition methods. The aim of this work was to synthesize polymeric material containing phthalic acid as a chelating resin for the enrichment of ultra-trace amounts Pb(II) ions.Display Omitted
Keywords: Enrichment; Pb(II); Phthalic acid; Sorption; Modified sorbent; Thermodynamics; Kinetics;

Formation of a thin polyaniline film on hydrous zirconia (ZrO2) surface was carried out using adsorbed surfactant bilayers on ZrO2 as reaction sites. Aniline was adsolubilized in hexadecyltrimethylammonium bromide (HDTAB) admicelles formed on the surface of ZrO2 by adsorption. Subsequent polymerization of the adsolubilized aniline monomer showed effective conversion of aniline to polyaniline. The formation of the polyaniline coated ZrO2 has been confirmed by UV–visible spectroscopy, FT-IR spectroscopy, and conductivity measurements. Various parameters involved during the adsorption process were studied. Selection of pH 9.0 as the pH of all experimental feed solutions was governed by the knowledge of point of zero charge (PZC) of ZrO2. Effect of aniline concentration on HDTAB adsorption was studied and it was observed that increase in aniline concentration decreased the amount of HDTAB adsorbed on ZrO2. Addition of salt (0.05 M NaCl) in the feed solution increased HDTAB adsorption and drastically reduced the effect of aniline concentration on HDTAB adsorption.
Keywords: Conducting polymers; Polyaniline; Hexadecyltrimethylammonium bromide; Admicelle; Hemi-micelle; Adsolubilization; Admicellar polymerization; Point of zero charge; Zeta potential;

Relaxation phenomena of hydrolyzed polyvinylamine molecules adsorbed at the silica/water interface by Otman Oulanti; Josiane Widmaier; Emile Pefferkorn; Simon Champ; Helmut Auweter (98-104).
Surface area exclusion chromatography was used to investigate the adsorption and reconformation characteristics of hydrolyzed polyvinylamine molecules at silica/water interfaces employing radiolabeled polymers. The polymer solution was injected at the inlet of the column, whereas the polymer was successively adsorbed on the stacked glass-fiber filters constituting the stationary phase of the column. The filters and effluent samples collected at the outlet were individually analyzed for radioactivity content, which provided the adsorption histogram and the relative affinity of the various polymers. For saturated polymer layers, the relaxation process was demonstrated when the exceedingly adsorbed molecules desorbed. Modifications in the adsorption on the successive filters were thus converted into changes in the interfacial area of adsorbed molecules, taking into account the deviation from the plateau adsorption expected for nonrelaxing systems. Adsorption characteristics of nonrelaxed polymer layers were determined from the adsorption values determined before relaxation occurred. Adsorption and relaxation characteristics were determined to depend strongly on molecular weight and degree of hydrolysis of the polyvinylamine molecules. Half-hydrolyzed polymers had adsorption and relaxation characteristics close to those of the fully hydrolyzed polyvinylamine. Accordingly, adsorption isotherms on the cellulose/water interface were carried out to possibly extend the main conclusions of the study.
Keywords: Hydrolyzed polyvinylamine; Polyvinylamine adsorption on silica; Polyvinylamine adsorption on cellulose; Polymer interfacial reconformation; Polymer layer relaxation; Surface area exclusion chromatography;

Relaxation phenomena of hydrolyzed polyvinylamine molecules adsorbed at the silica/water interface by Otman Oulanti; Emile Pefferkorn; Simon Champ; Helmut Auweter (105-111).
Surface area exclusion chromatography (SAEC) was employed to determine the individual relaxation of polymer molecules within a saturated heterogeneous layer composed of two polymers of different molecular characteristics. The investigations focused on three systems differing in molecular weight and/or hydrolysis grade. The molecular relaxation process was determined to be different within the heterogeneous layer when compared with the behavior of the same polymer in the homogeneous layer. The modifications in the relaxation process of a given polymer were imposed by the interfacial characteristics of the second polymer. Finally, in heterogeneous layers, the relative variation of the interfacial area of the two polymers is expressed in a single relationship.
Keywords: Hydrolyzed polyvinylamine; Polyvinylamine adsorption on silica; Heterogeneous polymer layers; Polymer interfacial reconformation; Polymer layer relaxation; Surface area exclusion chromatography;

Relaxation phenomena of hydrolyzed polyvinylamine molecules adsorbed at the silica/water interface by Otman Oulanti; Emile Pefferkorn; Simon Champ; Helmut Auweter (112-119).
Surface area exclusion chromatography (SAEC) was employed to determine the stability characteristics of saturated homogeneous layers when interfacial exchange or transfer of molecules was promoted. In these experiments, the first polymer layer was established by elution of a column composed of stacked glass-fiber filters with one polymer. Then, after displacement of the void by water, the second polymer was subsequently injected under the same elution conditions. The experiments combine polymers of equal or different molecular weight and/or hydrolysis grade. Histograms of SAEC experiments demonstrate the great stability of the initially adsorbed layer. Domains of high and low adsorption values were determined to exist along the chromatography column after injection of the first polymer sample. The polymer injected second slightly modifies the initial adsorption histogram and mainly overadsorbs on the low adsorption domain of the first polymer. The major result relates to the relaxation phenomenon affecting or not the second adsorbed polymer when it adsorbs on filters belonging to the low adsorption domain of the polymer first injected. The relaxation is impeded when the relaxation of the first polymer is of great amplitude, whereas it occurs when the relaxation of the first polymer is small.
Keywords: Hydrolyzed polyvinylamine; Polyvinylamine adsorption on silica; Heterogeneous polymer layers; Polymer interfacial exchange; Inhibition of layer relaxation; Surface area exclusion chromatography;

Monodisperse DNA restriction fragments by Karel L. Planken; Gijsberta H. Koenderink; Ramon Roozendaal; Albert P. Philipse (120-125).
We present a convenient and low-cost method to prepare milligram amounts of completely monodisperse DNA restriction fragments in a physico-chemical laboratory setting to study (in part II) the effect of limited flexibility on the concentration dependent sedimentation velocity. Four fragments of 200, 400, 800, and 1600 bp were designed to span a range of 1–11 persistence lengths. The fragments were synthesized by cloning fragments of controlled lengths obtained by PCR into bacterial plasmid DNA. The constructs were amplified in large-scale bacterial cultures from which the fragments were obtained by a modified alkaline lysis procedure and subsequent digestion with EcoRV. A method is presented to isolate the DNA from the digestion mixture using horizontal agarose-slab gels and agarose columns in a home-built preparative gel electrophoresis set-up. We show that a combination of optical absorbance readings, ethidium bromide fluorescence, and hyperchromicity measurements allows assessment of both the purity of the DNA solutions and the fraction of double-stranded DNA.
Keywords: DNA restriction fragments; Monodisperse colloidal rods; Preparative gel electrophoresis; DNA quality and quantity;

Monodisperse DNA restriction fragments by Gijsberta H. Koenderink; Karel L. Planken; Ramon Roozendaal; Albert P. Philipse (126-134).
We report sedimentation velocity and equilibrium measurements performed with an analytical ultracentrifuge to elucidate the effects of limited flexibility on the transport properties of semiflexible, monodisperse, double-stranded, blunt-ended DNA restriction fragments. We study a homologous series of fragments with 400, 800, and 1600 base pairs (3 to 11 persistence lengths), which are specifically designed and synthesized for this purpose (Part I). The molecular weights following from the sedimentation measurements agree well with the values expected on the basis of the number of base pairs. The sedimentation coefficients at infinite dilution are in good agreement with theoretical predictions for wormlike cylinders. The first order in volume fraction (ϕ) coefficient K of the ϕ-dependent sedimentation coefficient s ( ϕ ) = 1 − K ϕ decreases from 1178 for the shortest fragment to 882 for the longest fragment. These values are much larger than predicted for uncharged rigid rods, indicating the presence of associates with an enhanced aspect ratio and excluded volume. The precise match of the molecular weights obtained from exponential sedimentation–diffusion equilibrium distributions with weights calculated from the number of base pairs shows that any association is reversible and disappears at sufficiently low DNA concentration.
Keywords: Analytical ultracentrifugation; Monodisperse DNA; Sedimentation velocity/equilibrium; Rigid/semiflexible rods;

Fabrication of double-walled microspheres for the sustained release of doxorubicin by Eng Chew Tan; Rongyi Lin; Chi-Hwa Wang (135-143).
Double-walled microspheres with poly(L-lactic acid) shells and poly(DL-lactic–co-glycolic acid) cores were fabricated using solvent evaporation technique which involves the phase separation phenomenon of a binary composite of these two polymers. Doxorubicin, a hydrophilic drug, was entrapped within the core of these double-walled microspheres with different core–shell thicknesses and compositions to investigate the in vitro release on this class of microspheres. Microspheres of different size ranging from 50 to 300 μm were also fabricated to investigate whether this method is suitable for fabricating small particles for intramuscular injection applications, and their phase separation and surface morphology were examined by differential scanning calorimetry, scanning electron microscopy, and optical microscopy.
Keywords: Double-walled; Microsphere; Doxorubicin; Controlled release;

Stability and magnetic characterization of oleate-covered magnetite ferrofluids in different nonpolar carriers by M.T. López-López; J.D.G. Durán; A.V. Delgado; F. González-Caballero (144-151).
This work describes the preparation and stability evaluation of suspensions consisting of hydrophobic magnetite nanoparticles dispersed in different organic solvents. The ferrite particles are covered by a shell of chemisorbed oleate ions following a procedure that is described in detail. The oleate-covered particles were dispersed in different organic solvents with dielectric constants, ɛ r , ranging between 1.8 and 9, and the centrifugal field strength needed to remove particle aggregates formed during the synthesis was determined for the different liquid carriers used. A thermodynamic analysis demonstrated that the observed stability of the suspensions in liquids with ɛ r < 5 is well correlated with the very low lyophobic attraction between the particles. This can easily be surmounted by thermal agitation, since the van der Waals attraction is negligible. In contrast, for liquids with ɛ r > 9 , the suspensions become unstable because of the combined action of the van der Waals and lyophobic attractions, the latter being dominant for very polar solvents. Finally, a complete magnetic characterization of the oleate–magnetite powder, as well as of several stable ferrofluids prepared with it, was carried out. From this characterization, the magnetic diameters and magnetic moments of the particles immersed in the different liquid carriers were estimated and compared to those corresponding to the dry magnetic particles. This made it possible to estimate the thickness of the nonmagnetic layer on the particles.
Keywords: Ferrofluid; Magnetite nanoparticles; Oleic acid; Lyophobic attraction; Magnetic diameter; Magnetic moment; Saturation magnetization; Magnetic susceptibility;

This paper deals with the theoretical investigation of the effect of dust particles on a layer of a rotating ferromagnetic fluid heated from below saturating a porous medium subjected to a transverse uniform magnetic field. For a flat fluid layer contained between two free boundaries, an exact solution is obtained using a linearized stability theory and normal mode analysis. For the case of stationary convection, dust particles and nonbuoyancy magnetization always have a destabilizing effect, whereas rotation has a stabilizing effect on the onset of instability. In the absence of rotation, a destabilizing effect of medium permeability is depicted, but in the presence of rotation, medium permeability may have a destabilizing or stabilizing effect on the onset of instability. The critical wave number and critical magnetic thermal Rayleigh number for the onset of instability are also determined numerically for sufficiently large values of the buoyancy magnetization parameter M 1 and results are depicted graphically. It is observed that the critical magnetic thermal Rayleigh number is reduced solely because the heat capacity of clean fluid is supplemented by that of the dust particles. The principle of exchange of stabilities is found to hold true for the ferromagnetic fluid saturating a porous medium heated from below in the absence of dust particles and rotation. The oscillatory modes are introduced due to the presence of the dust particles and rotation, which were nonexistent in their absence. The sufficient conditions for the nonexistence of overstability are also obtained.
Keywords: Ferromagnetic fluid; Thermal convection; Porous medium; Dust particles; Rotation;

A synthetic method for preparing submicrometer-sized titania particles is proposed, which is based on hydrolysis of titanium alkoxide with the use of a cosolvent and an amine catalyst for alkoxide hydrolysis. The preparation was performed with different amines of ammonia, methylamine (MA), and dimethylamine (DMA) in different solvents of ethanol/acetonitrile, ethanol/methanol, ethanol/acetone, ethanol/acetonitrile, and ethanol/formamide for 0.1–0.3 M water and 0.03 M titanium tetraisopropoxide (TTIP) at temperatures of 10–50 °C. The use of the ethanol/acetonitrile solvent with MA was required for preparing monodispersed, spherical particles. The number average of the titania particle sizes and their coefficient of variation were varied from 143 to 551 nm and from 5.7 to 20.6%, respectively, with reaction temperature and concentrations of water and MA. Colloidal crystals of titania particles fabricated with a sedimentation method revealed reflection peaks attributed to Bragg's diffraction. Annealing at 100–1000 °C led to shrinkage and crystallization of titania particles followed by an increase in the refractive index of titania particles.
Keywords: Titania; Sol–gel method; Monodispersed particle; Colloidal crystal; Bragg's diffraction; Sedimentation;

The interaction between the anionic surfactant, sodium dodecyl sulfate, and the polyelectrolyte, poly(diallyldimethylammonium chloride), may lead to formation of nanoparticles dispersed in water. The morphology of the resulting nanoparticles and their ability to solubilize hydrophobic molecules were evaluated. As shown by SEM and AFM imaging, the particles are spherical, having a diameter of about 20 nm. The solubilization within the nanoparticles was tested with pyrene, a fluorescence probe, and Nile Red, a solvatochromic probe. It was found that for Nile Red the solubilization within the nanoparticles is at lower polarity than for SDS micelles, and from pyrene solubilization it appears that the hydrophobicity of the nanoparticles depends on the ratio between the SDS molecules and the charge unit of the polymer.
Keywords: SDS; PDAC; Surfactant; Polymer; Nanoparticles; Solubilization; Pyrene; Nile Red; CAC; CMC;

One-step synthesis of Mn3O4 nanoparticles: Structural and magnetic study by América Vázquez-Olmos; Rocío Redón; Geonel Rodríguez-Gattorno; M. Esther Mata-Zamora; Francisco Morales-Leal; Ana L. Fernández-Osorio; José M. Saniger (175-180).
One-step room-temperature synthesis of nanocrystalline Mn3O4 hausmannite, without heating posttreatment, was carried out from a simple dissolution of manganese(II) acetate in a mixture of N, N ′ -dimethylformamide (DMF) and water. Homogeneous nanocrystals like rods were obtained, with an average width and length of 6.6 ± 1.2   nm and 17.4 ± 4.1   nm , respectively, and a preferential growth along the 〈 001 〉 direction. Magnetization measurements on a powdered sample showed ferrimagnetic behavior at low temperatures. Under zero-field cooling (ZFC) measurement at 100 Oe, the observed blocking temperature (T B) was 37 K.
Keywords: Nanoparticles; Hausmannite; Colloidal dispersion; Magnetic materials;

Stability of dispersions of colloidal alumina particles in aqueous suspensions by Bimal P. Singh; Ruben Menchavez; Chika Takai; Masayoshi Fuji; Minoru Takahashi (181-186).
The colloidal stability of suspensions of alumina particles has been investigated by measuring particle size distribution, sedimentation, viscosity, and zeta potential. Alumina particles were found to be optimally dispersed at pH around 3 to 7.8 without dispersant and at pH 8.5 and beyond with dispersant. The above results corroborate zeta potential and viscosity measurement data well. The surface charge of alumina powder changed significantly with anionic polyelectrolyte (ammonium polycarboxylate, APC) and the iep shifted toward more acidic range under different dispersant conditions. It was found that the essential role played by pH and dispersant (APC) on the charge generation and shift in the isoelectric point of alumina manifests two features: (i) the stability decreases on approaching the isoelectric point from either side of pH, and (ii) the maximum instability was found at pH 9.1 for alumina only and at pH 6.8 for alumina/APC, which is close to the isoelectric points for both the system, respectively. Using the model based on the electrical double-layer theory of surfactant adsorption through shift in isoelectric points, the authors could estimate the specific free energy of interaction (7.501 kcal/mol) between particles and dispersant. The interaction energy, zeta potential, sedimentation, and viscosity results, were used to explain the colloidal stability of the suspension.
Keywords: Alumina; Zeta potential; Isoelectric point; Dispersion volume; Specific interaction energy;

Comparative real-time characterization of frother bubble thin films by Stéphanie Gélinas; James A. Finch; Maxime Gouet-Kaplan (187-191).
Methylisobutyl carbinol (MIBC) and methoxy polypropylene glycol (Dowfroth 250) bubble thin films were characterized by composition and thickness determinations, using FT-IR spectroscopy and UV–visible spectrophotometry, respectively. The infrared investigation indicates that the role of frother molecules in creating bubble thin films is based on their effectiveness in inducing H-bonding reorganization of the surrounding free water molecules into a coherent network. From UV–visible interference patterns, it is found that MIBC forms films with a measured critical end thickness of less than 160 nm, compared to 612 ± 30   nm for Dowfroth 250. The observed values of the free water layer thickness are comparable at 5.65 ± 0.28   μm for MIBC and 6.75 ± 0.34   μm for Dowfroth 250. A higher stability of an MIBC bubble over a Dowfroth 250 bubble is related to the different polarization and orientation of the molecules sustaining the boundary surface water network. The findings are used to explain the different action and associated froth characteristics of the two common industrial frothing agents.
Keywords: Frothers; Flotation; Bubbles; Thin films; Spectroscopy;

Zinc stable isotope fractionation during its adsorption on oxides and hydroxides by O.S. Pokrovsky; J. Viers; R. Freydier (192-200).
Adsorption of Zn on goethite, hematite, birnessite, pyrolusite, corundum, and gibbsite was studied using a batch adsorption technique as a function of pH, zinc concentration in solution, and time of exposure. Adsorption from 0.01 M NaNO3 solutions undersaturated with respect to zinc (hydr)oxide at 3 < pH < 8 was found to be reversible and equilibrium was achieved in less than 24 h. A 2pK surface complexation model that assumes the constant capacitance of the electric double layer (CCM) and postulates the formation of positively charged >MeO―Zn+ complexes, where Me = Fe, Mn, and Al, was used to describe the dependence of adsorption equilibria on aqueous solution composition in a wide range of pH and Zn concentration. The logarithms of surface stability constant for Zn interaction with metal oxy(hydr)oxides (>MeOH0  +Zn2+  ⇒ MeO―Zn+) vary from −2.5 to 0.5. They are higher for oxy(hydr)oxides than for anhydrous oxides. Stable isotopes of zinc in several filtrates were measured using an ICP-MS Neptune multicollector which made it possible, for the first time, to assess the degree of isotopic fractionation between 66Zn and 64Zn during zinc adsorption on mineral surfaces. The isotopic offset between aqueous solution and mineral surfaces (Δ66/64Znsoln/solid=δ(66/64Zn)solutionδ(66/64Zn)surface) was found to be weakly dependent on percentage of adsorbed metal and equals 0.20 ± 0.03 , 0.17 ± 0.06 , − 0.10 ± 0.03 , − 0.10 ± 0.09 , and − 0.13 ± 0.12 ‰ for goethite, birnessite, pyrolusite, corundum, and Al(OH)3. For hematite, Δ66/64Zn varies from − 0.61 ± 0.10 ‰ at pH 5.5 to − 0.02 ± 0.09 ‰ at 5.8 < pH < 6.7. Overall, zinc stable isotopic fractionation induced by adsorption on most mineral surfaces does not exceed 0.2‰. We do not observe any correlation between the sign and magnitude of isotopic offset and the chemical nature of solid phase (hydrous versus anhydrous minerals), zinc surface adsorption constants (surface complexation model of the present work), and coordination and first-neighbor distances of surface >MeO―Zn(H2O) n complexes (available literature data on X-ray absorption spectroscopy). Apparently, the fine structure of surface complexes and the position and bond strength for second neighbors of zinc are likely to control its isotopic fractionation during adsorption on mineral surfaces. Our results strongly suggest that inorganic processes controlling zinc isotope adsorption on soil and sediment minerals should be of second-order importance compared to biological factors.
Keywords: Zinc; Adsorption; Iron; Aluminum; Manganese; Oxide; Hydroxide; Surface complexation; Stable isotopes; Fractionation;

Knowledge-based reconstruction of random porous media by N. Eschricht; E. Hoinkis; F. Mädler; P. Schubert-Bischoff; B. Röhl-Kuhn (201-213).
An evolutionary optimization technique is used to reconstruct digitized material models of 3003 nm3 size for mesoporous two-phase systems. The models are adapted to the two-point probability (TPP) and to a volume-based pore-size distribution (PSD) which were derived from SANS and adsorption experiments and which carry statistical information about morphology and topology of the pore system. To avoid extreme update-costs, the bulk of mutations are assessed by means of a suitable approximation of the PSD; it is demonstrated that a sporadic insertion of the PSD suffices to drive the algorithm towards satisfactory models in acceptable time. Our approach is knowledge-based in the sense that (i) the mutations are restricted to expedient exchanges of phase-voxels by a heuristic rule, and (ii) the sporadic calculation of the PSD from the current state of the model, in essence, provides an efficient self-control for the evolutionary process. We applied the method to reconstruct periodic models of the xerogel Gelsil 200. Such reconstructs of real mesoporous solids could be utilized, for instance, to verify theories of adsorption and capillary condensation. A self-controlling evolutionary algorithm is applied to reconstruct a highly porous xerogel by means of morphological descriptors gained from SANS and adsorption data.Display Omitted
Keywords: Knowledge-based reconstruction; Evolutionary optimization; SANS; Pore size distribution; Two-point correlation; Porous media; Xerogel;

Low-temperature ionic liquids immobilized in porous alumina by M. Kosmulski; M. Szafran; C. Saneluta; K. Marczewska-Boczkowska (214-217).
The pores in an aluminum oxide matrix can be completely filled with 1-alkyl-3-methylimidazolium tetrafluoroborates, hexafluorophosphates, triflates, and bis(trifluoromethylsulfonyl)imides. This possibility can be utilized to produce solid electrolytes for batteries and fuel cells. Porous alumina after 75 days in 1-hexyl-3-methylimidazolium trifluoromethanesulfonate at 80 °C.Display Omitted
Keywords: Porous ceramics; Ionic liquid; Composites; Electrical properties;

Layered double hydroxide hybrids with dicetylphosphate by Toshio Itoh; Tetsuya Shichi; Tatsuto Yui; Katsuhiko Takagi (218-222).
Dicetyl phosphate (DCP) ions incorporated into layered double hydroxide (LDH) clays to form a DCP/LDH hybrid were prepared and structurally characterized by X-ray diffraction analysis, scanning electron microscopy, thermogravimetry, and differential thermal analyses. DCP was concluded not only to form well-aligned bilayer structures along the vertical axis of the LDH layers but also to be arranged in a distorted hexagonal packing orientation in the lateral planes within the DCP/LDH hybrid interlayers. DCP forms not only well-aligned bilayer structures but could also be arranged in a distorted hexagonally packed orientation within the DCP/LDH hybrid interlayers.Display Omitted
Keywords: Dicetyl phosphate; Clay; Layered double hydroxide; Hydrophobic interaction;

Adsorption of fluids in slitlike pores containing a small amount of mobile ions by M. Borówko; K. Bucior; S. Sokołowski; T. Staszewski (223-228).
We apply density functional theory to investigate changes in the phase behavior of a fluid caused by the presence of mobile ions inside the pore. The approach has been based on the fundamental measure density functional theory and on the theory of nonuniform electrolytes developed recently by O. Pizio, A. Patrykiejew, S. Sokołowski [J. Chem. Phys. 121 (2005) 11,957]. We have evaluated capillary condensation phase diagrams for pores of different widths and for different concentrations of confined ions. The calculations have demonstrated that the presence of ions leads to lowering the critical temperature and to an increase of the value of the chemical potential at the capillary condensation point.
Keywords: Capillary condensation; Slitlike pore; Density functional theory; Ionic solution;

In this work, the effect of chemical modification on the surface energetics and cure kinetics of carbon blacks (CBs) modified with KOH and C6H6 was investigated by contact angle and rheometer measurements, respectively. Also, the resulting mechanical properties of the CBs/styrene–butadiene composites were studied in terms of tensile and dynamic mechanical analysis. As experimental results, the polar basic and nonpolar chemical treatments showed an increase of the London dispersive component ( γ S L ) of γ S of the CBs without significantly changing the surface properties and microstructures that resulted from the deaggregation of microstructures and decrease of the swollen weight of the sample in the equilibrium state. Also, it was clearly revealed that the increase of γ S of the CBs could largely affect the vulcanization and mechanical properties of the composites, resulting from the increase in γ S L of the CBs. These results were evident that the mechanical properties of the composites were controlled more by the γ S L of γ S than by the specific (or polar) component ( γ S SP ), including electron acceptor and donor parameters on CB surfaces in an organic matrix composite system.
Keywords: Chemical modification; Surface energetics; Carbon blacks (CBs); Styrene–butadiene rubber (SBR); Mechanical properties;

Interfacial properties and foam stability effect of novel gemini-type surfactants in aqueous solutions by Durga P. Acharya; José M. Gutiérrez; Kenji Aramaki; Ken-ichi Aratani; Hironobu Kunieda (236-243).
Static and dynamic surface tension and interfacial rheological behavior of a novel anionic gemini-type surfactant without a spacer group, sodium 2,3-didodecyl-1,2,3,4-butane tetracarboxylate (GS), were investigated. Very low values for critical micelle concentration ( 8.9 × 10 −5  M ) as well as equilibrium surface tension (22.7 mN m−1) were observed for the aqueous solutions. Dynamic surface tension (DST) is very slow and less sensitive to the surfactant concentration than the conventional monomeric surfactant, suggesting the presence of a significant adsorption barrier for GS owing to a complicated molecular structure. Presence of a small concentration of GS in sodium dodecyl sulfate (SDS) solution shows a synergistic effect to form mixed micelles and lowers the cmc considerably. This synergism between GS and SDS and slow exchange of GS between bulk and interface create a rigid air–liquid interface of the SDS–GS solution, which is reflected in a higher elasticity value for the interface of the SDS–GS solution than for the SDS solution. It has been found that the presence of a small concentration of GS in SDS solution increases the foam stability noticeably. Although the stability of the wet foam is correlated with the film elasticity, the stability of dry foam cannot be explained in terms of film elasticity alone.
Keywords: Gemini surfactants; Interfacial tension; Dynamic surface tension; Dilatational elasticity; Foam stability;

The new hydrophobic azo dye 4-(N-phenyl-N-decylamino)- 4 ′ -nitroazobenzene (AzoC10) has been synthesized. It is compared with 4-(N-phenylamino)- 4 ′ -nitroazobenzene (Azo) in terms of reactivity ( k iso of the thermal cis  →  trans isomerization, microsecond flash photolysis) and of the solvatochromic behavior ( λ max of the trans-isomer, UV/vis absorption), respectively, within membrane mimeting amphiphile microstructures in aqueous solutions of poly(ethylene oxide) m –poly(propylene oxide) n –poly(ethylene oxide) m micelles and of extruded vesicles. The temperature-induced micelle formation and phase transitions in bilayers of vesicles, respectively, caused characteristic discontinuous changes of k iso and λ max with temperature. They differ between the two dyes due to their different solubilization sites and different impact on their microenvironment. In micelles forming aqueous polymer surfactant solutions, two azo dyes show very different temperature behavior of thermal cis–trans isomerization rates.Display Omitted
Keywords: Azo dyes; UV/vis spectroscopy; Rate constants; Cistrans isomerization; Micelles; PEO–PPO–PEO triblock copolymers; Unilamellar vesicles; Temperature behavior; Phase transition;

The specificity of interphase transfer of organic reagents of different types between water and the nonionic-surfactant-rich phases at the cloud point temperature was investigated. In contrast to organic solvents, the ability of the micellar phases to extract highly charged ions of organic reagents was shown. Further evidence of the specificity of interphase transfer in micellar-extraction systems is independent and cooperative influence of substrate molecular structure and hydrophobicity on their distribution. The appearance of host–guest phenomenon in cloud point extraction systems that is inherent in organized systems with molecules of the receptors was established. The possibility of describing reagent distribution using regressions that consider substrate hydrophobicity and molecular structure in the cloud point extraction systems was shown.
Keywords: Cloud point extraction; Nonionic surfactant; Distribution coefficient; Dyes;

Dilute emulsions of dodecane in water were prepared under constant flow rate conditions with binary surfactant systems. The droplet size distribution was measured as a function of the mixed surfactant composition in solution. The systems studied were (a) the mixture of anionic sodium dodecyl sulfate (SDS) with nonionic hexa(ethyleneglycol) mono n-dodecylether (C12E6) and (b) the mixture of cationic dodecyl pyridinium chloride (DPC) with C12E6. At a constant concentration of SDS or DPC surfactant in solution (below the CMC) the mean emulsion droplet size decreases with the increase in the amount of C12E6 added to the solution. However, a sharp break of this droplet size occurs at a critical concentration and beyond this point the mean droplet size did not significantly change upon further increase of the C12E6. This point was found to corresponded to the CMC of the mixed surfactant systems (as previously determined from microcalorimetry measurements) and this result suggested the mixed adsorption layer on the emulsion droplet was similar to the surfactant composition on the mixed micelles. The emulsion droplet size as a function of composition at the interface was also studied. The mean emulsion droplet size in SDS–C12E6 solution was found to be lower than that in DPC–C12E6 system at the equivalent mole fraction of ionic surfactant at interface. This was explained by the stronger interactions between sulphate and polyoxyethylene head groups at the interface, which facilitate the droplet break-up. Counterion binding parameter (β) was also determined from zeta-potential of dodecane droplets under the same conditions and it was found that (β) was independent of the type of the head group and the mole fraction of ionic surfactant at interface.
Keywords: Binary surfactant mixtures; Surfactant head groups; Emulsification; Emulsifier droplet size; Nonionic/ionic surfactants;

This article is the first part of a two-part study that exemplifies how to treat the solubilization of water in multicomponent surfactant-based systems. In particular, it aims at clarifying the role of cosurfactants in water solubilization in these systems. The judicious selection of the components in such systems to maximize water solubilization is occasionally thought to be dictated by the chain length compatibility principle, which may be expressed quantitatively by the BSO (Bansal, Shah, O'Connell) equation. Here we demonstrate some limitations of the equation. For example, in our best model system, C12(EO)8/dodecane + pentanol = 1:1 (by weight)/water at 27 ± 0.2 ° C , the BSO equation predicts that no alcohol is needed for maximum water solubilization, contrary to our experimental findings. We discuss how to optimize the alcohol/oil weight ratio needed for stabilizing four-component microemulsions. In our model systems C12(EO)8 or C18:1(EO)10/pentanol/dodecane/water, this optimal weight ratio is 1:1. We also highlight the difference between the effect of normal alcohols on water solubilization—which passes via a maximum—and their effect on percolation processes and structured changes of proteins, which depends solely upon the alcohol hydrophobicity. For the investigation of the effect of branching on phase behavior the utilization of an extended form of the geometrical branching factor F b is suggested. The meaning of this factor is elucidated by comparing it with topological indices.
Keywords: Nonionic microemulsions; Water solubilization; BSO equation; Branching factor;

In this second part of a paper dealing with the effect of branched alcohols on solubilization, an attempt has been made to provide explanations of experimental data related mostly to the system Brij 97/branched alcohol + dodecane = 1:1 (by weight)/water at 27 ± 0.2  °C . Applying the Hou–Shah mechanism it was shown that for many C4–C6 branched alcohol isomers having one methyl branch, solubilization behavior is readily interpreted by assuming control of the critical radius, R c . Two parameters, both included in the definition of the branching factor, F b (which was treated in the first part of the paper), were also used to analyze solubilization data. The first, l i , is defined as the distance from the free end of the alcohol molecule to the methyl branch. The second, d, is virtually N A , the chain length of the alcohol. When l i > 3 , the solubilization becomes dominated by the natural radius of curvature, R 0 . Also, we have suggested that for R c -control, solubilization will be enhanced in direct proportion to the distance d – l i , whereas for R 0 -control, solubilization will increase with decreasing d – l i . The validity of our assumptions was demonstrated in many cases. Some examples of the more complicated case of double branching (two methyl groups along the alcohol chain) were also analyzed.
Keywords: Solubilization; Microemulsion; Hou–Shah mechanism; Branching factor;

Transient electrophoresis of dielectric spheres by Huan J. Keh; You C. Huang (282-291).
The dynamic electrophoretic response of a spherical dielectric particle suspended in an electrolyte solution to a step change in the applied electrics field is analytically studied. The electrical double layer surrounding the particle may have either a small but finite thickness or a very large thickness relative to the particle radius. For the case of electrophoresis of a particle with a thin double layer, the local electroosmotic velocity at the outer edge of the double layer evolving with time after the external field is imposed is used as an apparent slip boundary condition at the particle surface so that the unsteady equation of motion for the fluid flow outside the double layer is solved. Closed-form formulas for the transient electrophoretic mobility of the particle are derived as functions of relevant parameters. The results demonstrate that, when the double layer surrounding the particle is relatively thin, the normalized electrophoretic mobility at a given dimensionless time decreases monotonically with a decrease in the parameter κa, where κ −1 is the Debye screening length and a is the particle radius. When the double layer of the particle is relatively thick, the particle mobility can have magnitudes comparable to those for a particle with a thin double layer in the initial stage, but will become much smaller afterward. In general, the effect of the relaxation time for transient electrophoresis is negligible, regardless of the value of κa.
Keywords: Electrophoresis; Electroosmosis; Transient response; Step-function electric field;

Macroporous ZrO2 ceramics prepared from colloidally stable nanoparticles building blocks and organic templates by Yu Jia; Cihangir Duran; Yuji Hotta; Kimiyasu Sato; Koji Watari (292-295).
ZrO2 macroporous materials with well-ordered structures were prepared using nano-ZrO2 particles as the building materials and polystyrene spheres as the organic templates. A well-dispersed nano-ZrO2 suspension with a narrow particle size distribution was prepared by deagglomeration of as-received nano-ZrO2 powders via ultrasonication, and then centrifugation was performed to remove agglomerated bigger particles. Negatively charged polystyrene spheres were uniformly coated with positively charged nano-ZrO2 particles by means of electrostatic attraction at pH 4. Green samples were prepared by slip casting from colloidally stable suspension of nano-ZrO2 coated polystyrene spheres. ZrO2 macroporous materials with well-ordered microstructure derived from the nano-ZrO2 coated polystyrene spheres. ZrO2 macroporous materials with well-ordered structures were prepared by using nano-ZrO2 particles as the building materials and polystyrene spheres as the organic templates.Display Omitted
Keywords: ZrO2; Nanoparticles; Dispersion; Coating; Macroporous materials; Colloidal processing;

Linear stability analysis for a film on a solid surface with a viscoelastic air–liquid interface is presented. The interfacial dilatational and shear viscoelastic properties were described by Maxwell models. Dilatational and shear interfacial elasticity and viscosity were shown to improve film stability. When the interfacial rheological properties are extremely large or small, the maximum perturbation growth coefficient is shown to reduce to those for immobile and mobile interfaces respectively. Calculated values of maximum growth coefficient for thin film stabilized by 0.5% β-lactoglobulin approached those of mobile films for thick ( > 2000   nm ) and those for immobile films for thin ( < 100   nm ) films respectively with the values lying between the two limits for intermediate film thicknesses. Linear stability analysis for a film on a solid surface with a viscoelastic air–liquid interface, described by a Maxwell model, is presented.Display Omitted
Keywords: Film stability; Viscoelastic interface; Surface dilatational viscosity; Surface dilatational elasticity; Surface shear viscosity; Surface shear elasticity; Perturbation growth coefficient; Thin film on solid; Maxwell model; Viscoelasticity; Linear stability;

Lanthanum(III) and gadolinium(III) separation by cloud point extraction by Niels De Jong; Micheline Draye; Alain Favre-Réguillon; Gérard LeBuzit; Gérard Cote; Jacques Foos (303-306).
In the present study, cloud point extraction (CPE) is used with lipophilic chelating agents, 8-hydroxyquinoline (HQ) and Kelex 100 (K100), to extract and separate lanthanum(III) and gadolinium(III) from aqueous solutions. The methodology used is based on the formation of lanthanide(III) organic complexes that are soluble in a micellar phase of a non-ionic surfactant, Triton X-114. The lanthanide(III) complexes are then extracted into the surfactant-rich phase at a temperature above the cloud-point temperature. Influence of pH of the solution, structure of the chelating agent, chelating agent/lanthanides(III) molar ratio, on extraction efficiency and selectivity is studied. High extraction efficiency and selectivity for Gd(III) is observed using HQ whereas K100 is a poor extractant. By pH switching, yields of Gd(III) recovery higher than 95% were obtained with selectivity factors up to 37 against La(III), indicating the feasibility of separating Gd(III) from La(III) using CPE.
Keywords: Cloud point extraction; Lanthanide(III); 8-Hydroxyquinoline; Kelex 100; Stripping;

by Arthur Hubbard (307).