Journal of Colloid And Interface Science (v.294, #2)

(iii-viii).

Adsorption of Basic Yellow 28 from aqueous solutions with clinoptilolite and amberlite by Julide Yener; Turkan Kopac; Gulsen Dogu; Timur Dogu (255-264).
The objective of this study was to investigate the adsorption of Basic Yellow 28 that is a cationic dye on clinoptilolite and amberlite XAD-4. Both equilibrium and batch rate adsorption in aqueous solutions of the dyestuff were investigated. Adsorption rate data were analysed using the pseudo-first order kinetic model of Lagergren and the pseudo-second order model to determine adsorption rate constants at 20, 30 and 40 °C. The adsorption equilibrium data were analysed using various adsorption isotherm models and the results have shown that adsorption behaviour of Basic Yellow 28 by clinoptilolite and amberlite could be described by either Langmuir or Freundlich models. Langmuir adsorption isotherm constants corresponding to adsorption capacity, Q 0 , were found to be 59.6, 52.9 and 56.7 mg/g for clinoptilolite at 20, 30 and 40 °C, respectively. Lower adsorption capacities for Basic Yellow 28 on amberlite were obtained. The increase of adsorption rate constants with an increase in temperature for BY 28 adsorption on amberlite indicated chemisorption with dissociation and increased availability of sites due to higher penetration of adsorbing molecules into the pores.
Keywords: Clinoptilolite; Amberlite XAD-4; Basic Yellow 28 dye; Adsorption isotherms; Adsorption rate;

Mechanistic modeling of arsenic retention on natural red earth in simulated environmental systems by Meththika Vithanage; Rohana Chandrajith; Athula Bandara; Rohan Weerasooriya (265-272).
Arsenic retention on natural red earth (hereafter NRE) was examined as a function of pH, ionic strength, and initial arsenic loading using both macroscopic and spectroscopic methods. Proton binding sites on NRE were characterized by potentiometric titrations yielding an average pHzpc around 8.5. Both As(III)– and As(V)–NRE surface configurations were postulated by vibration spectroscopy. Spectroscopically, it is shown that arsenite forms monodentate complexes whereas arsenate forms bidendate complexes with NRE. When 4 < pH < 8 and [total arsenic as As(III) or As(V)] = 0.385 μmol/L both arsenite and arsenate exhibit near 100% adsorption for a 10-fold variation of ionic strength that is ascribed to inner-sphere complexation of surface bonding. Arsenite exhibits an apparent bond-switching mechanism from inner-sphere to outer-sphere at excess As(III) loading (total arsenic as As(III) or As(V)] = 38.5 μmol/L. Competitive effect of arsenate for arsenite adsorption sites was observed when [initial As] = 0.385 μmol/L. In dual adsorbate systems the Γ As(III) was reduced over 20%, showing a competition of arsenite for arsenate binding sites (or vice versa). All experimental data were quantified with a 2pK generalized diffused layer model considering two site types for both protons and anions binding using reaction stoichiometries, as follows: FeOH + H+ ⇔ FeOH+ 2, 4.744, FeOH ⇔ FeO + H+, −9.03, AlOH + H+ ⇔ AlOH+ 2, 7.229, AlOH ⇔ AlO + H+, −9.316, FeOH(s) + H3AsO3(aq) ⇔ FeHAsO2− 3(s) + H2O, 6.798, AlOH(s) + H3AsO3(aq) ⇔ AlHAsO2− 3(s) + H2O, 5.319, FeOH(s) + H2AsO 4(aq) ⇔ FeHAsO2− 4(s) + H2O, 11.88, AlOH(s) + H2AsO 4(aq) ⇔ AlHAsO2− 4(s) + H2O, 9.061.
Keywords: Surface complexation; Generalized diffuse layer; Arsenite; Arsenate; Competitive adsorption; Natural red earth;

Energy of adsorption interaction and surface coverage from polymer of various molecular structures by Yuri Lipatov; Valentine Chornaya; Tamara Todosijchuk; Galina Menzheres (273-280).
Adsorption from solutions of mixtures of polymers which considerably differ by the parameter of thermodynamics flexibility (σ) has been studied at various components ratio. Initial and equilibrium concentrations of solutions were determined, surface coverage (θ) and energy of adsorption interaction (Q, kJ/mol of segments) were estimated by means of IR spectroscopy. The objects of investigation were: cis-1,4-polybutadiene rubber (PB) and cellulose triacetate (CTA). Aerosil (fumed silica) was used as an adsorbent. Analysis of the experimental data testifies that polymer polarity and its affinity to the surface have the decisive influence on the adsorption. Polar stiff chain CTA has greater affinity to the surface of adsorbent and correspondingly has greater adsorption activity as compared with flexible, but nonpolar PB. The values of energy of adsorption interaction and surface coverage obtained under the adsorption from polymer systems first of all depend on whether the stiff chain polar component or flexible chain nonpolar component prevails in the system. Increase of concentration of the nonpolar PB flexible chain in the system results in diminishing of summary energy of adsorption interaction, but its great flexibility at the same components ratio provides the maximal values of surface coverage. The greater values of the surface coverage under the adsorption from the solutions of polymer mixtures in comparison with the individual solutions are explained by the simultaneous adsorption of both components for all concentration intervals.Adsorption from solutions of mixtures of cis-1,4-polybutadiene rubber (PB) and cellulose triacetate (CTA) has been studied. Figure shows dependence of the adsorption interaction energy (Q) on the surface coverage ( θ ) .
Keywords: Adsorption; Polymer mixture solutions; Polymer chain flexibility (stiffness); Surface coverage; Energy of adsorption interaction;

The equilibrium and dynamics of levulinic acid sorption on two weakly basic anion exchangers, in free base form, in single-component aqueous solutions were investigated. Adsorption isotherms such as Langmuir, Sips, Radke–Prausnitz, and Toth were applied to correlate the experimental data in the temperature range 285 – 315   K . Modeling results showed that the Toth model is the best one to correlate the sorption isotherms. The resulting Toth equations were used with the Clausius–Clapeyron equation to determine the isosteric heat of sorption. The sorption kinetics was experimentally measured via a completely stirred finite-bath batch experiment under different initial concentrations and at varying solution temperatures. The pseudo-second-order kinetic model and the Elovich equation were used to represent the kinetic data and the equation parameter values were also evaluated. The pseudo-second-order equation cannot simulate the experimental kinetic data, while the Elovich equation fitted the sorption dynamic data very well under all the operating conditions studied. Finally, the apparent activation energy of sorption was also determined.
Keywords: Levulinic acid; Anion exchanger; Sorption equilibrium; Batch kinetics; Toth; Elovich; Pseudo-second order; Isosteric heat;

We study the surface phase behavior in Langmuir monolayers of a series of nonionic surfactants of the general formula CnE1 with n = 14 , 16, and 18 by film balance and Brewster angle microscopy (BAM) over a wide range of temperatures. A cusp point followed by a pronounced plateau region in the pressure–area ( π – A ) isotherms indicates a first-order phase transition in the coexisting state between a lower density liquid expanded (LE) phase and a higher density liquid condensed (LC) phase at the air–water interface. The formation of bright two-dimensional (2D) LC domains in a dark background visualized by BAM further confirms this observation. In addition to the cusp point at the onset of the LE–LC coexistence state, another cusp point followed by a small plateau is observed for the C14E1 and C18E1 monolayers, indicating a second phase transition between two condensed phases of different compressibility and tilt orientation of the molecules. This unusual two-step phase transition is explained by the Ostwald step rule. The C16E1 and C18E1 monolayers show a kink in their respective isotherms, after which the surface pressure increases steeply with only a little decrease in the molecular area, suggesting that the molecules undergo a transition from a tilted to an almost vertical orientation with respect to the water surface. The thermodynamic parameters for the condensation of the molecules in the LE–LC coexistence state were calculated by employing the 2D Clapeyron equation. The temperature coefficient of the critical surface pressure d π c / d T values shows a decreasing trend from C14E1 to C18E1, suggesting that the condensation process becomes less and less prone to thermal perturbation as the chain length increases. For all the amphiphiles, the ΔH values are found to be negative, suggesting an exothermic nature of condensation. The negative ΔS values obtained from the relation Δ H / T probably come from the restriction on the rotational and translational motion of the molecules constrained in a confined area in the LE–LC transition region.
Keywords: Nonionic surfactants; Langmuir monolayers; Brewster angle microscopy; Phase transition; Condensed-phase domains;

Nonfibrous β-structured aggregation of an Aβ model peptide (Ad-2α) on GM1/DPPC mixed monolayer surfaces by Takayoshi Kawasaki; Kentaro Asaoka; Hisakazu Mihara; Yoshio Okahata (295-303).
Adsorption and aggregation of transformed peptides and proteins onto the cell membrane surface is commonly associated with forms of amyloidosis such as Alzheimer's disease and prion disease. To address dynamic features of these pathological phenomena molecularly, the in situ Ad-2α model peptide deposition on glycolipid-containing monolayers was studied by using a 9 MHz quartz-crystal microbalance (QCM). The Ad-2α peptide has two amphiphilic α-helix segments, each modified with a 1-adamantanecarbonyl group at the N-terminal as a hydrophobic defect. The peptide folds in a 2α-helix structure in the bulk solution. In the presence of mixed monolayers of glycolipids (GM1, asialo-GM1, GM3, or LacCer) and/or dipalmitoyl phosphatidylcholine (DPPC) laminated on the QCM plate, the peptide deposition and the conformational change to β-structure on the monolayers were accelerated. The adsorption kinetics and the amount of Ad-2α were dependent on the sort and contents of the glycolipid in the DPPC matrix. Although the Ad-2α peptide adsorbs onto most of the glycolipid membranes as monolayer coverage, it adsorbed largely onto the GM1/DPPC (30/70 mol%) mixed monolayer with characteristic kinetic behaviors. The accumulation of β-structured nonfibrous aggregations was confirmed by AFM and fluorescence microscopy with Thioflavin T (ThT).
Keywords: Amyloid peptide; Quartz-crystal microbalance; Ganglioside mixed monolayers; Thioflavin T; AFM;

Preferential adsorption of dipeptide diastereomers (dialanine, Val-Ala) on clay mineral surfaces was observed. Significantly higher adsorption of dipeptides composed from only one type of enantiomer of amino acid units in comparison to those containing both L- and D-type of amino acid units in their molecules, was experimentally proven. This selectivity was explained in terms of different hydrophobic properties of diastereomers, which are probably controlled by intramolecular interactions between nonpolar and polar parts of dipeptide molecules affected by their stereochemistry. A significantly higher reactivity of stereoisomers composed from the same type of amino acid enantiomers to form amide bonds was proven as well. Theoretical study could distinguish different properties of the diastereomers. The results of the calculations indicate possible effects of molecular stability in the stereoselectivity during the adsorption and reactions of Ala2 diastereomers.This paper describes the stereoselectivity in adsorption and subsequent reactions of dipeptide stereoisomers forming amide bonds in montmorillonite suspension. Significantly higher adsorption and reactivity of dipeptides composed of only one type of enantiomer of amino acids (L–L or D–D) was proven.
Keywords: Adsorption; Diastereomers; Dipeptides; Clay minerals; Chemical evolution;

Microstructure formation in dip-coated particulate films by L. Günther; W. Peukert; G. Goerigk; N. Dingenouts (309-320).
The microstructure-dependence of dip-coated particulate thin films on the stability of an aqueous silica sol used as coating bath is studied. Different stability conditions are adjusted in the sol by changing electrolyte concentration and pH value. Care was taken to avoid pronounced aggregation of the particles before the coating process. The characterization of the stability behavior gives clear evidence of a non-DLVO contribution at low pH values that is attributed to hydration forces. Structural evolution of the particulate network during film formation is studied using a dialysis accumulation procedure. The viscosity of the accumulated sol is measured as a function of shear rate and related to the drying characteristic of the coating process. Atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and N2 sorption are used to obtain information on the surface and volume structure of the dip-coated films. The structure of coatings is found to distinctly vary with stability parameters. This is attributed to changing interactions during the first drying stage. Finally, the influence of coating structures on the light transmission properties is determined. A comparison between the extinction of the uncoated and the coated substrate revealed a difference of up to ± 50 % in dependence on the microstructure.The influence of particle interactions on both structure formation and dry film structure of dip-coated particulate silica films has been studied. The relevance of particle interactions for tailoring film microstructure and thereby macroscopic coating properties is demonstrated.
Keywords: Dip coating; Particles; Colloidal stability; Film structure; Pore size distribution; Rheology; Small-angle scattering;

The physiochemical nature of the metal–extractant species in organic solvent has been a matter of debate over liquid–liquid extraction of transition metals by bis(2-ethylhexyl) phosphate. The aggregation behavior of nickel(II), cobalt(II), lead(II), and zinc(II) bis(2-ethylhexyl) phosphate have been investigated using molecular modeling. The recently confirmed “open” water channels rodlike reversed micelles which is in contact with the nonaqueous solvent rather than in an inner core (or “closed” water channel) of the nickel–extractant species by Ibrahim and Neuman appears to be a unique structure for such species. Lead–, cobalt– and zinc–extractant species behave in a different manner. The cobalt–extractant species form rodlike reversed micelles, but does not show the formation of any open water channel. The zinc– and lead–extractant species form ellipsoidal (or deformed spherical) reversed micelles with fewer water molecules located at the core of the micelles which is in accord with the conventional view of reversed micelles. The structural variations of the reversed micelles for the metal extracted species are in accord with the known extraction behavior of such metals when using HDEHP.The “open water-channel” model of Ni(DEHP)2 reversed micelles is a unique structure. Other metal–extractant species form reversed micelles that are in accord with the conventional view of reversed micelles.
Keywords: Reversed micelles; HDEHP; Solvent extraction; Divalent metals; Molecular modeling;

Solvothermal synthesis of hollow ZnS spheres by Zhengshui Hu; Lanying Li; Xiaodong Zhou; Xun Fu; Guohua Gu (328-333).
Mono-dispersed semiconductor ZnS hollow spheres with the diameter of 300–500 nm and the shell thickness of about 100–150 nm have been synthesized successfully by solvothermal method from ethanol solution in the presence of a special surfactant—quaternary ammonium salt of 2-undecyl-1-dithioureido-ethyl-imidazoline (SUDEI) made in our lab. The mono-dispersed ZnS hollow spheres are characterized by XRD, size distribution investment, UV–vis, TEM, and SEM, respectively. The UV–vis measurement indicates that there is a broad absorption at 210–280 nm, which is likely to be caused by “hollow-effect.” A growth mechanism of ZnS hollow spheres has also been put forward and discussed.
Keywords: ZnS hollow spheres; Hollow-effect; Solvothermal;

Size tunable synthesis of cysteine-capped CdS nanoparticles by γ-irradiation by Anindita Chatterjee; Amiya Priyam; Satyen K. Das; Abhijit Saha (334-342).
Highly water soluble and biocompatible L-cysteine-capped CdS nanoparticles having narrow size distribution were synthesized for the first time by γ-irradiation technique without using any additional stabilizer. FTIR study shows that CdS nanoparticles are capped through mercapto-group of cysteine amino acid while its free amino and carboxylate groups make it amenable to bio-conjugation. Size and luminescence of the nanoparticles can be well controlled by varying the parameters like radiation dose, pH and concentration of cysteine. The observed results suggest that pH 7 can be optimum for the synthesis of L-cysteine-capped CdS nanoparticles. CdS nanoparticles synthesized with molar ratio of Cd2+:cysteine, 1:60 at pH 7 were found to be most luminescent. All nanoparticles formed lie in the size quantization regime and exhibit good crystallinity. Remarkable improvement in stability and luminescence was achieved on changing pH of as-prepared nanoparticles from 7 to 11.
Keywords: CdS nanoparticles; Cysteine; γ-Irradiation; Luminescence; Stability;

Lines of dense nanoparticle colloidal suspensions evaporating on a flat surface: Formation of non-uniform dried deposits by A.L. Yarin; J.B. Szczech; C.M. Megaridis; J. Zhang; D.R. Gamota (343-354).
Line evaporation of dense nanoparticle suspensions is studied theoretically and experimentally. The 2-D lines are drawn by a pen-like nozzle continuously dispensing a commercially available concentrated organic suspension (50 wt%; 4.3 vol%) of 5 nm gold nanoparticles in toluene solvent. Such particle-containing lines show promise for industrial applications where circuits are inkjet-printed and heat-treated to dry off the organic solvent and sinter the nanoparticles, thus producing a continuous electrically conducting path. The employed nanosuspension displays spontaneous thickening upon contact with a solid surface in the ambient atmosphere, and thus does not dry according to the well-established coffee-stain forming mechanism applicable to dilute particle suspensions. In the present work, model lines (∼1 mm width) are studied to elucidate the drying peculiarities of such nanoparticle slurries. These scaled-up lines allow detailed spatial measurements of their topography throughout their prolonged evaporation period, and make possible direct comparisons between experiment and theory. The results show the particle deposits formed by evaporative drying of these lines to be of non-uniform thickness with a dent in the middle of the lateral cross-section. Formation of this practically undesirable landscape is attributed to the highly non-uniform evaporative character of sessile or pendent liquid lines, which results in a non-uniform consolidation of the porous phase formed upon contact with the solid surface. The formulated description of the shape changing process, as done in the framework of the consolidation theory, yields predicted deposit speck shapes that compare favorably with the temporally resolved experimental data.
Keywords: Nanoparticle colloidal suspension; Evaporating slurry line; Drying; Film deposit;

Spherical iron/silica nanocomposites from core-shell particles by Manuel Ocaña; Manuel Andrés-Vergés; Raúl Pozas; Carlos J. Serna (355-361).
A simple procedure to coat silica spheres with smooth layers of iron compounds is reported. It is based on the forced hydrolysis (60–85 °C) of iron(III) acetylacetonate solutions containing the silica cores and sodium dodecylsulfate (SDS). The role that the iron(III) precursor and SDS play in the formation of uniform coatings is discussed. The thermal evolution of the composites up to the crystallization of the initially amorphous coating was also studied. Finally, the core-shell particles, as prepared, were thermally reduced under hydrogen atmosphere to produce magnetic composites whose magnetic properties were also evaluated as a function of the reduction temperature.Magnetic iron/silica nanocomposites were prepared from core-shell spherical particles by thermal reduction with hydrogen and their magnetic properties were modulated by varying the reduction temperature.
Keywords: Core-shell; Coating; Iron; Iron oxide; Silica; Magnetic properties;

Surface modification of mechanochemically activated kaolinites by selective leaching by Éva Makó; Zsuzsa Senkár; János Kristóf; Veronika Vágvölgyi (362-370).
Low- and high-defect kaolinites mechanochemically activated for different periods of time have been treated with sulfuric acid solution. These modified materials were analyzed using a combination of X-ray diffraction, thermogravimetry, chemical analysis, diffuse reflectance Fourier transform infrared spectroscopy, as well as specific surface area and pore size distribution measurements. In addition to the mechanochemically amorphized part, the disordered and the adequately distorted phases also reacted with sulfuric acid. The specific surface areas of the leached samples of the partially or the completely amorphized materials were found to be greater than those of the thermally amorphized ones. The acid treatment results in a greater total pore volume for the partially amorphized materials than for the totally amorphized mineral. The partially amorphized high-defect kaolinite was proved to be more soluble than the low-defect kaolinite under similar conditions.Instead of calcination (H), it is the mechanical activation of Zettlitz (Z) and Szegi (Sz) kaolins that combined with acid treatment (L) proved to be effective to produce porous silica with high total pore volume.
Keywords: Dry grinding; Kaolinite; Mechanochemical activation; Selective leaching;

The interaction of a water-soluble ABA type of dumbbell-shaped polyethyleniminated copolymers (D400(EI)8) with H2PtCl6 in aqueous medium is studied by means of UV–visible absorption spectra, dynamic light scattering (DLS) measurements, and transmission electron microscopy (TEM). From TEM images of the stained polymer, it is evident that the spherical and well-structured polymer micelles are formed by the introduction of H2PtCl6, and totally nonstructured micelles are formed from D400(EI)8 itself. These findings coincide with the results obtained from DLS measurements, where the narrowly distributed polymer aggregates are remarkably observed. Moreover, it is directly evidenced from TEM that the reduced Pt(0) nanoparticles are embedded in the polyethylenimine (PEI) block at the exterior of micelles, whereas the polyoxypropylene (PPO) block is surrounded by the PEI block. Additionally, the resulting Pt(0) colloids are very stable for at least 4 months.
Keywords: Polyethyleniminated copolymer; Salt-induced micelles; Platinum nanoparticles;

Anoxic dissolution of troilite in acidic media by Paul Chiriţă; Michaël Descostes (376-384).
The anoxic dissolution of troilite (FeS) in acidic medium has been investigated at 50 °C using batch dissolution experiments. Two different progress variables were followed during solid dissolution, i.e., the amounts of dissolved iron ( n Fe ) and formed hydrogen sulfide ( n H 2 S ). The experimental studies performed at hydrogen ion concentrations ([H+]) ranging from 0.04 to 0.2 mol L−1 showed that anoxic dissolution of troilite is dependent on [H+]. The cumulative release of both Fe and H2S could be described by a diffusion-like rate law, with rate constants for Fe ( k Fe p ) always greater than for H2S ( k H 2 S p ). The surplus of dissolved iron over formed hydrogen sulfide was quantified by the n Fe : n H 2 S ratio, and ranged from 1.21 to 1.46, higher than the specific n Fe : n H 2 S ratio of troilite bulk, i.e., 1. Rate constants are linearly related to the pH with a slope of 0.66 ± 0.23 ( n Fe ) or 0.63 ± 0.13 ( n H 2 S ). The obtained results suggest that troilite anoxic dissolution is a process controlled by the diffusion of the reaction products across an obstructive layer, sulfur-rich layer (SRL), having a thickness that increases during reaction progress. The accumulation of H2S between the surface and the SRL, eventually leads to the mechanical destruction of this outer layer, a process that results an increased flux of reaction products.The integral form of rate law that can describe within experimental uncertainties the troilite anoxic dissolution is: n Fe = 0.85 ( ± 0.50 ) [ H + ] 0.66 ( ± 0.23 ) t 0.5 for dissolved iron and n H 2 S = 0.58 ( ± 0.21 ) [ H + ] 0.63 ( ± 0.13 ) t 0.5 for released H2S .
Keywords: Troilite; Hydrogen sulfide; Dissolved iron; Anoxic dissolution; Reaction mechanism; Diffusion;

Two peptides based on the active SIKVAV sequence were synthesized and hydrophobically modified through attachment of a myristoyl residue to the amino terminal group. A comparative study was carried out on the physicochemical properties of both parent and hydrophobically modified structures. Properties studied were hydrophobicity, surface activity, spreadability on aqueous surfaces, penetration in lipid monolayers, aggregation and haemolytic activity. Results obtained indicate that myristoyl containing peptides form micelles at 10−6 M concentration, whereas parent peptides start to aggregate at 10−5 M. All of them are able to spread on aqueous surfaces forming stable monolayers. Concerning their haemolytic activity only one of the sequences promotes a partial lysis of erythrocytes after 30 min incubation at 37 °C and 10−5 M concentration in the media.
Keywords: Peptide synthesis; Monomolecular layers; Laminin; Fluorescence; Surface activity; Phospholipids;

It is shown that the interface shrinkage resulting from the capillary pressure difference between both sides of a curved interface is the product of a “standard shrinkage”κγ (κ is the isothermal compressibility, γ the interfacial tension) by a dimensionless factor that depends only on the shape of the sample of matter under study. The behaviour of the standard shrinkage in the critical domain shows that it cannot be a measure of the thickness of the liquid–vapour interface in that domain. The standard shrinkage of classical liquids somewhat above triple point is usually near to 0.048 v c 1 / 3 ( v c is the critical molecular volume); exceptions to this rule are discussed. The variation of the standard shrinkage along the liquid–vapour coexistence curves of water and argon is presented; the effect of the interface shrinkage on the measured surface tension of liquids can become important within about 15% of the critical temperature. The standard shrinkage of solids is less than that of the corresponding liquids, and is of no consequence when measuring the surface tension of solids. The standard shrinkage of the nuclear fluid is 0.23 fm = 0.09 v c 1 / 3 . The saturation density of infinite nuclear matter is about 9% less than its value in atomic nuclei, and a term proportional to A 1 / 3 (A is the mass number) must be added to the nuclear binding energy formula.
Keywords: Surface energy; Thermodynamics of surfaces and interfaces; Critical exponents; Nuclear matter; Nuclear binding energies and masses;

Wetting properties at the surface of iota-carrageenan-based edible films by Thomas Karbowiak; Frédéric Debeaufort; Dominique Champion; Andrée Voilley (400-410).
Surface properties of edible films composed of a polymeric matrix of carrageenan in association with hydrophobic material were studied by contact angle measurements. The use of this technique not only in a static mode but also in a dynamic way enables investigation of surface hydrophobicity as well as surface wettability. The absorption flux inside the material can be estimated from the wetting kinetic, which can be very useful to quickly compare water barrier efficiency of the tested films. Comparison of carrageenan films with films containing known amounts of additives enables understanding and correlation of changes of the surface properties with the nature of used additives (glycerol used as a plasticizer, glycerol monostearate used as a surfactant, and fat) and their influence on the orientation of polymer chains at the surface during film formation. Very different responses were observed from one surface of the film (film-casting–support interface) to the other (film–air interface), which could be also attributed to the influence of the support on the polymer and to macromolecular orientation during drying after casting.
Keywords: Edible film; Carrageenan; Contact angle; Water; Absorption; Surface;

The dynamic interfacial tension for binary mixtures of hydrophobic metal ion extractants and a modifier were measured by using the drop volume technique. Four types of equimolar mixtures were considered: two chelating extractants: 2-hydroxy-5-nonylacetophenone oxime (HNAF) and β-diketone (1-phenyldecan-1,3-dion), two solvating extractants: trioctylphosphine oxide (TOPO) and tributyl phosphate (TBP), chelating and solvating extractants TOPO and β-diketone, and the chelating extractant HNAF and the modifier (decanol). With the aid of the Ward and Torday equation the values of the diffusion coefficients of individual compounds and their equimolar mixtures were estimated. It was found that in the case of two types of investigated mixtures, i.e., HNAF + β-diketone and HNAF + decanol the compound HNAF that was dominant in the mixed adsorbed monolayer and the more interfacially active also determined the kinetics of adsorption in mixed systems. In contrary to the mixture of two chelating reagents, in the case of a mixture of two solvating extractants the mixed system behaves like the less active, though dominant at the interface, reagent TBP. The same effect was observed in both of the considered diluents (toluene and octane).
Keywords: Liquid/liquid interface; Dynamic interfacial tension; Solvent extraction; Hydrophobic metal ion extractants; Mixed adsorbed monolayer; Diffusion coefficient;

One of the simplest methods of measuring the quantities for estimating the adhesion properties of materials (i.e., the adhesion work, the surface energy, and the interfacial tension between certain liquids and a surface) requires the determination of the contact angle between the liquid and the surface. In the case of plane surfaces the determination of the drop dimensions makes it possible to calculate the contact angle by the sessile drop method, but in the case of cylindrical surfaces (such as the monofilaments), several methods were developed to improve the accuracy of the contact angle measurements. This paper presents a comprehensive method for precise evaluation of the contact angle between liquid drops and monofilaments by establishing a differential equation describing the drop contour. This equation makes it possible to accurately compute the contact angle using the dimensions of the drop. A comparison of the values of the contact angle calculated by our method and those obtained by other approaches is made. We applied our method in the case of polyamide-6 monofilaments treated using dielectric barrier discharge, knowing their medical applications in surgical sutures.This paper presents a method to evaluate the contact angle between liquid drops and monofilaments, by establishing a differential equation which allows to compute the contact angle using the dimensions of the drop.
Keywords: Adhesion work; Biocompatibility; Contact angle measurement; Cylindrical surfaces; Liquid–solid interface;

Investigations on foamability of surface-chemically pure aqueous solutions of functionalized alkylaldonamides by Dorota Piłakowska-Pietras; Klaus Lunkenheimer; Andrzej Piasecki (423-428).
The foamability of the aqueous solutions of functionalized, surface-chemically pure surfactants of the nonionic saccharide-type: N , N -di-n-alkylaldonamides, N-alkyl-N-(2-hydroxyethyl)aldonamides, and N-cycloalkylaldonamides, derivatives of D-glucono-1,5-lactone and/or D-glucoheptono-1,4-lactone, were investigated. The approach of Lunkenheimer and Małysa for the characterization of the foamability and foam stability of these surfactant solutions was applied for these investigations. Using standard parameters related to the different physical stages of the foaming process, foam stability can be described in a simple and easy manner. In general, the investigated alkylaldonamides form foams of medium stability. However, for some homologues a transition from unstable to stable foam systems is observed with increasing concentration. Modifications of the molecular structure of the alkylaldonamides are distinctly reflected in their foam properties. This fact concerns not only changes of the hydrophobic moiety and its functionalization but also slight variations of the saccharide residue. Each homologous series reveals an exceptional foam behavior. In the case of the N , N -di-n-alkylaldonamides the increase of the n-alkyl chain length is accompanied by an increase of the foam stability. The aqueous solutions of the N-alkyl-N-(2-hydroxyethyl)aldonamides reveal most favorable foaming properties for homologues with average alkyl chain lengths. Moreover, it was found that the occurrence of a phase transition in the adsorption layers of the N-cyclooctylgluconamides previously observed by surface tension and surface potential measurements is also remarkably reflected in their foam stability.
Keywords: Sugar surfactants; Aldonamides; Foamability;

Interfacial behavior of DEHEHP and the kinetics of cerium(IV) extraction in nitrate media by Junmei Zhao; Xiaobo Sun; Wei Li; Shulan Meng; Deqian Li (429-435).
The effects of diluents, temperature, acidity, and ionic strength of the aqueous phase on the interfacial properties of DEHEHP have been extensively investigated using the Du Nouy ring method. In addition, the effect of cerium(IV) concentration loaded in the organic phase on the interfacial tension has also been studied. With the increase of DEHEHP concentration, the value of interfacial tension (γ) decreases in the studied system, which shows that DEHEHP has interfacial activity as a kind of surfactant. The surface excess at the saturated interface ( Γ max ) and the minimum bulk concentration of the extractant necessary to saturate the interface ( C min ) under the different conditions are calculated according to two adsorption equations such as the Gibbs and Szyszkowski functions to be presented in comprehensive tables and figures. The relationship between the interfacial activity of DEHEHP and cerium(IV) extraction kinetics by DEHEHP has been discussed by considering different factors such as the effects of diluents and temperature. However, the interfacial activity parameter of extractant only is a qualitative parameter, but cannot provide strong enough evidence to quantitatively explain the relationship between extraction kinetics and interfacial properties of an extractant.
Keywords: DEHEHP; Interfacial behavior; Cerium(IV); Extraction; Kinetics; HNO3;

The membrane emulsification process is becoming of growing interest in many industrial fields. For monitoring the influence of process and membrane parameters on the droplet formation, quantitative information on the droplet detachment, during this process, is important. Until now, droplet formation has theoretically been described using computational fluid dynamics and global force equations. Unlike computational fluid dynamics methods, the global force models are less accurate but easier to handle and instructive. On this basis, in the present paper we present new force balance equations to describe droplet detachment during cross-flow membrane emulsification. In a first approximation, the droplet is supposed to grow leaning on the pore border as long as a force balance exists along the contact line located on the membrane surface. During this phase the base of the droplet, still stuck on the pore border, begins to bend on the membrane surface until its final detachment. Using force balance equations made along the contact lines, we obtain the minimum and maximum sizes that a droplet could have during cross-flow membrane emulsification. This approach is tested with different continuous phase velocities, membrane pore sizes and interfacial tensions. The results are compared to various experimental data, reported in literature. In particular, based on the experimentally found linear correlation between droplet and pore sizes, we show how the proposed balance equations can be used to obtain a satisfactory evaluation of the slopes of this linear correlation and how these force balances could be used to obtain an estimation of the interfacial tensions during the droplet formation.A new force balance, using advanced and receding contact angles, is proposed to describe the droplet detachment during a cross-flow membrane emulsification. This force balance evaluates the droplet deformations along its contact line due to the continuous phase crow-flow.
Keywords: Cross-flow membrane emulsification; Force balance; Contact lines; Advancing and receding contact angles; Mean droplet sizes; Interfacial tensions; Droplet formation mechanisms;

In this paper, mixtures of sugar-based decanoyl-N-methylglucamide with three different n-alkyltrimethylammonium bromides ( n = 12 (DTAB), 14 (TTAB), and 16 (CTAB)) have been studied using conductance and fluorescence spectroscopic techniques. The critical micelle concentration values of pure and mixed systems were determined by both the conductance and the pyrene 1:3 ratio methods. The experimental results were interpreted using thermodynamic mixing approaches based on the pseudophase separation model. These analyses allowed us to determine the interaction parameters and the composition of the mixed micelles through the whole composition range. Since all the ionic surfactants used in this study have the same headgroup, the differences observed between the three mixed systems were attributed to the lengths of their hydrocarbon chains. It was established that, besides interactions of electrostatic character, additional short-range interactions must be considered. By using the static quenching method, the mean micellar aggregation numbers of mixed micelles were obtained. In the cases of the mixed systems with DTAB and TTAB it was observed that the aggregation number is initially reduced with the participation of the ionic component, remaining almost constant and close to the aggregation number of the pure ionic micelle. However, in the systems involving CTAB it is observed that the size of micelles initially increases and then decreases slightly for mixtures with a high content of the ionic component. The hydrophobic index pyrene 1:3 ratio was used to examine possible changes in the micellar micropolarity; however, no definitive conclusions could be derived from these experiments. In order to study the evolution of the local viscosity of the mixed micelles upon addition of the ionic surfactant, fluorescence polarization measurements were carried out with two different probes, fluorescein and coumarin 6. It was found that the participation of the ionic component in the mixed micelle induces the formation of less ordered structure than that of pure nonionic micelles. An attempt was made to correlate these effects with the interaction parameters obtained from the theoretical mixing model and, consequently, with the alkyl chain length of the ionic components.This report describes an investigation on the mixed micellization process between the nonionic surfactant decanoyl-N-methylglucamide (MEGA-10) with three different n-alkyltrimethylammonium bromides ( n = 12 (DTAB), 14 (TTAB), and 16 (CTAB)).
Keywords: Mixed micelles; MEGA-10; n-Alkyltrimethylammonium bromides;

The critical micelle concentration of tetraethylammonium perfluorooctylsulfonate in water by José L. López-Fontán; Alfredo González-Pérez; Julian Costa; Juan M. Ruso; Gerardo Prieto; Pablo C. Schulz; Félix Sarmiento (458-465).
The aggregation characteristics of tetraethylammonium perfluorooctylsulfonate in water were studied by several techniques: conductivity, pH, ion-selective electrodes, and surface tension. It was concluded that the aggregation process is gradual and starts with the formation of oligomers such as ion pairs that grow to give spherical micelles, which become wormlike with increasing concentration. Because of the size and hydrophobicity of the counterion, micelles quickly increase in ionization degree up to about 0.5. Differences among different critical micelle concentration values in the literature are explained on the basis of the gradual formation of micelles.This work reports the Krafft point of tetraethylammonium perfluorooctylsulfonate, and the dependence on temperature of the critical micelle concentration, the micellar ionization degree and Gibbs free energy, enthalpy and entropy of micellization, the apparent molar partial volume, thermal expansion coefficient, and the adiabatic compressibility factor of both micellized and unmicellized surfactant in water. Results are interpreted on the basis of dehydration of surfactant on micellization and on the temperature increase.
Keywords: Tetraethylammonium perfluorooctylsulfonate; Critical micelle concentration; Premicelles; Perfluorinated surfactants; Air/solution interface;

Flow properties of freshly prepared ettringite suspensions in water at 25 °C by Camelia M. Vladu; Christopher Hall; Geoffrey C. Maitland (466-472).
The rheology of a complex, heterogeneous mineral colloid was rationalised using models devised for model rod systems. Mixing a calcium hydroxide slurry with an aluminium sulphate solution produces a suspension of rod-shaped ettringite particles. Ettringite rod suspensions exhibit non-Newtonian flow behaviour, which depends on the shape of the particles, their size distribution, concentration and surface properties as well as the suspension medium characteristics. We have measured the shear viscosity of suspensions of ettringite rods with a median aspect ratio, r i ∼ 8, at 25 °C as a function of particle volume fraction, ϕ, in the range 0.0001–0.08. It was found that the viscosity of the suspensions increased with ϕ, and showed a marked change of slope at ϕ ∼ 0.01 , which we identified as the minimum overlap concentration ϕ * . Above ϕ * , the system is in the semi-dilute regime. At ϕ > ϕ * , when Pe rot > 1 , hydrodynamic interactions between rods become increasingly significant, and we observe shear-thinning behaviour. The high effective hydrodynamic volume of rotating rods, resulting in much lower values of the maximum packing fraction, ϕ c , than for spheres, dominates the rheological behaviour of ettringite suspensions.The ettringite particles were well-characterized by electron microscopy so that the effect of shape and size on the shear rheology was successfully studied.
Keywords: Rheology; Morphology; Ettringite;

Streaming potential measurements across charged membranes separating two equal solutions have been carried out. Two cation-exchange membranes with different cross-linked and swelling properties (Ionics and Nafion membranes) and methanol–water electrolyte solutions of KCl have been used in the experiments. The obtained results show that the streaming potential is higher for the Ionics membrane and that the values depend on the methanol content of the solutions. A different behavior is found in the dependence of the streaming potential on the methanol percentage for each membrane. The study of the relaxation times in the decay of electrokinetic steady states of streaming potential has been carried out from the time dependence of the streaming potential when the pressure difference through the membrane is suppressed. The results show the existence of two different parts or partial relaxations, mechanical and electric. A different behavior of the mechanical relaxation time with the methanol percentage has been found for the two membranes, but any significant difference between their electric relaxation times. These differences have been explained in terms of the different degree of swelling of the membranes used.The pressure coefficient of two cation-exchange membranes with different cross-linked and swelling properties (Nafion and Ionics membranes) has been estimated in methanol–water electrolyte solutions of different methanol percentages.
Keywords: Streaming potential; Cation-exchange membranes; Relaxation times; Methanol–water solutions;

Studies of the sample transport in a microchannel with the electrical conductivity gradient are critical to develop techniques for on-chip sample transport control. A numerical model presented in this paper, consisting of the electrical potential equation, full Navier–Stokes equation and species conservation equation, is used to simulate sample transport in a microchannel with the consideration of the conductivity gradient. There are two situations studied here, sample pumping (where sample separation is minimized by employing a high-conductivity buffer in the sample region), and sample stacking (where sample separation is expedited by using a low-conductivity buffer as the sample carrier). The effects of applied electrical potential, sample diffusion coefficient and the ratio of conductivity of the driving buffer over the sample carrying buffer are investigated by using the developed model.Centerline axial concentration profiles for the transport of a two-analyte sample, where the conductivity of the sample-carrying buffer is higher than that of the driving buffer (pumping protocol).
Keywords: Electrokinetics; Conductivity gradient; Microfluidic devices; Sample manipulation; Numerical simulation;

The electrostatic potential in a capillary filled with electrolyte is derived by solving the nonlinear Poisson–Boltzmann equation using the method of matched asymptotic expansions. This approach allows obtaining an analytical result for arbitrary high wall potential if the double layer thickness is smaller than the capillary radius. The derived expression for the electrostatic potential is compared to numerical solutions of the Poisson–Boltzmann equation and it is shown that the agreement is excellent for capillaries with radii greater or equal to four times the electrical double layer thickness. The knowledge of the electrostatic potential distribution inside the capillary enables the derivation of the electroosmotic velocity flow profile in an analytical form. The obtained results are applicable to capillaries with radii ranging from nanometers to micrometers depending on the ionic strength of the solution.Analytical expressions for electrostatic potential distribution and electroosmotic flow in cylindrical capillaries are obtained using the method of matched asymptotic expansions. The results are applicable for moderately thin double layers.
Keywords: Charged capillary; Nanofluidics; Microfluidics; Thin double layer; Electrostatic potential; Electroosmotic flow; Matched asymptotic expansions;

Electrorheological behavior of copper phthalocyanine-doped mesoporous TiO2 suspensions by Kai Di; Yihua Zhu; Xiaoling Yang; Chunzhong Li (499-503).
A type of anhydrous electrorheological (ER) material of copper phthalocyanine (CuPC)-doped mesoporous TiO2 was synthesized by in situ micelle-assisted incorporation CuPC during mesoporous TiO2 synthesis. TEM, XRD and the nitrogen adsorption–desorption isotherms demonstrated that the material had mesoporous structure and an anatase framework. The ER behavior of the suspensions of CuPC-doped mesoporous TiO2 in silicone oil with the different volume fractions was investigated under an applied electric field. It is found that the suspensions showed visible electrorheological behavior which were compared with that of pure TiO2. The dopants of CuPC molecules within the mesochannel of TiO2 mesoporous sieve improved the conductivity of the particles and produced a proper conductivity of ∼10−7 S m−1. Dielectric spectra of the ER fluid were measured to examine the peak of ɛ ″ should appear in the frequency range of 102–105 Hz and have a large Δ ɛ ′ in this frequency range. Therefore, the both properties may make a conjunct effect on electrorheological behavior.A new anhydrous ER fluid composed of CuPC-doped mesoporous TiO2 particles and methylic silicone oil has been investigated. When the CuPC/CTAB molar ratio is increasing, the yield stress is obviously increasing.
Keywords: Electrorheological fluid; Mesoporous TiO2; Interfacial polarization; Dielectric property;

Visible light photocatalytic decomposition of 2-naphthol by anodic-biased α-Fe2O3 film by Tetsuro Kawahara; Kei-ichi Yamada; Hiroaki Tada (504-507).
Transparent α-Fe2O3 films with varying film thickness were formed on a SnO2 transparent conducting film-coated glass substrate by metal organic deposition. Under anodic-biased conditions, the α-Fe2O3 film showed a high photocatalytic activity for the decomposition of 2-NAP with visible light irradiation. The α-Fe2O3 is transformed to inactive hydroxide as the reaction proceeds, while the activity of α-Fe2O3 is almost maintained in acetonitrile.Under anodic biased conditions, the α-Fe2O3 film formed on a SnO2 film-coated glass has showed a high photocatalytic activity for the decomposition of 2-naphthol with visible light irradiation.
Keywords: Photoelectrochemistry; Visible-light photocatalyst; α-Fe2O3; Fe(OH)3; Thin film;