Journal of Colloid And Interface Science (v.301, #2)

The soap-free emulsion polymerization has been applied for preparing the surfactant-free polystyrene/layered double hydroxide exfoliated nanocomposite. The XRD and TEM determinations have been used to monitor the changes of interlayer spacing and morphology during polymerization. The results show that the obtained nanocomposite has the homogeneous structure of polymeric and inorganic components. Due to the absence of organic surfactant, the PS/LDH nanocomposite shows a remarked improvement on the onset decomposition temperature compared with virgin PS.TEM micrograph shows that the LDH layers have been disorderly exfoliated in PS/LDH nanocomposite prepared via soap-free emulsion polymerization.
Keywords: Nanostructure; Polymer/layered double hydroxide (LDH) nanocomposites; Soap-free emulsion polymerization; Thermal properties;

A model is proposed to account for the interaction energy and adhesion force between petroleum asphaltenes and metallic surfaces. It is assumed that the total molecule-surface interaction potential may be constructed through superposition of corresponding interactions with a relevant number of atomic layers forming the substrate and resorting to the Lindhard continuum planar potential (CPP) approximation, which requires only of knowledge of binary molecule-atom interactions. Molecular mechanics (MM) calculations are performed to generate the average binary interaction between the asphaltene molecule and an atom in the substrate, which in turn is represented by a parameterized analytical—physically sound—expression. The resulting CPP yields an analytical expression representing the interaction between the asphaltene molecule and each substrate layer. To validate the method, pilot calculations are performed for a sample asphaltene molecule with a fixed orientation relative to metallic surfaces of iron, aluminum, and chromium. Comparison between corresponding CPP and MM calculations for the asphaltene-plane (A-P) and asphaltene-substrate (A-S) interactions indicate reasonable agreement pointing to the adequacy of the CPP method to represent molecule-surface interactions. Also, the effect of a surrounding (i.e., solvent) medium is addressed with the use of a dielectric constant, ε, incorporated in the molecule-atom potential. Finally, a discussion is presented on the applicability of the method to generate an analytical universal expression for asphaltene-metallic wall interactions.A model based on the continuum planar potential approximation is proposed to account for the interaction energy and adhesion force between petroleum asphaltenes and metallic surfaces.
Keywords: Asphaltene adhesion; Metallic surfaces; Adhesion force; Analytical model;

Adsorption of a series of ethoxylated cationic surfactants at model surfaces of alkanethiol self-assembled monolayers was studied by the surface plasmon resonance technique. Model surfaces were tailor-made by choosing alkanethiols or mixtures of alkanethiols with methyl, hydroxyl, carboxyl, and trimethylammonium groups in terminal position. The ethoxylated and quaternized cationic surfactants having from 2 to 18 oxyethylene units, showed a decrease in adsorbed amount with increasing oxyethylene chain length for both hydrophobic and hydrophilic surfaces. On a negatively charged surface, containing carboxylate groups, the surfactant with only two oxyethylene groups adsorbed strongly due to electrostatic attraction and the adsorption increased with increasing amount of surface carboxylate groups. This work shows the usefulness of self-assembled alkanethiols on gold as a tool for performing surfactant adsorption studies on surfaces with variable hydrophobicity and charge.
Keywords: Cationic surfactant; Adsorption; Self-assembled monolayer; Surface plasmon resonance;

pH effect on phosphate sorption by crystalline MnO2 by Syed Mustafa; Muhammad Iqbal Zaman; Sadullah Khan (370-375).
The phosphate anions sorption on manganese dioxide was studied as a function of pH in the range 3–9 and at 293 K. The sorption was observed to increase with the increase in concentration of phosphate and decrease with the increase in pH. No effect of the phosphate adsorption upon the PZC of the solid suggested that the only outer sphere complexes were formed on the surface of the solid. The potentiometric titrations studies of the solid were also performed in the presence of different phosphate concentrations (0.53, 1.053, and 2.11 mmol L−1). The calculated pKa values showed that the solid protonation played a dominant role in the uptake of phosphate anions by the solid.The pH changes accompanying the phosphate sorption show that it has very little effect upon the charging mechanism of the MnO2 due to the formation of outer sphere complexes.
Keywords: Manganese dioxide; Point of zero charge; Sorption; Surface complexation; Potentiometric titrations;

Molecularly smooth cellulose surfaces for adhesion studies by Ronny Sczech; Hans Riegler (376-385).
Cellulose is deposited on silicon wafer surfaces via spin coating from a solution of cellulose in dimethylacetamide ( + 7 % lithium chloride). The resulting cellulose layers were analyzed by ellipsometry, AFM, FTIR, ICP-MS, X-ray reflectivity, and contact angle measurements. For cellulose concentrations below 0.07 wt% the wafer surfaces are covered with a network of cellulose fibrils. For concentrations between 0.07 and 0.5 wt%, closed films with thicknesses between 1.5 and ≈10 nm are obtained. These films are molecularly smooth (rms roughness < 2 nm). Higher concentrations result in thicker films with significantly rougher surfaces (rms roughness > 2 nm). The cellulose layers were used to investigate cellulose/cellulose adhesion and their modification by polyelectrolytes. To this end the sticking behavior of cellulose beads was analyzed. It is demonstrated that the sticking of the beads depends on the type, amount, and adsorption symmetry of adsorbed polyelectrolyte. Low, incomplete polyelectrolyte coverage always enhances sticking, whereas for high coverage the symmetry of the polyelectrolyte coating is very important. In this case, sticking (adhesion) is enhanced if only one surface is covered with polyelectrolyte prior to contact. If both surfaces were fully covered with polyelectrolytes before contact, sticking (adhesion) is decreased.3D-view and thickness profile of a region with and without cellulose film (scratched off with the tips of tweezers). The thickness profile is taken from an averaged box of 2 × 3   μm along the edge.
Keywords: Cellulose; Adhesion; Polyelectrolytes; Cellulose surfaces; Thin films;

The complex dynamic surface elasticity of the solutions of copolymer of sodium 2-acrylamido-2-methyl-1-propansulfonate with N-isopropylacrylamide and dodecyltrimethylammonium bromide was measured as a function of the surfactant concentration and the surface age by the oscillating bubble and drop methods. The kinetic dependencies of the surface elasticity proved to be non-monotonic at low concentrations and the main features of the surface viscoelasticity differed from the results for other polyelectrolyte/surfactant solutions films studied so far. The observed peculiarities were connected with the properties of the copolymer chain.The complex dynamic surface elasticity of the solutions of copolymer of AMPS-NIPAM and DTAB was measured as a function of the surfactant concentration and the surface age by the oscillating bubble and drop methods. The kinetic dependencies of the surface elasticity proved to be non-monotonic at low concentrations and the main features of the surface viscoelasticity differed from the results for other polyelectrolyte/surfactant solutions layer studied so far. The observed peculiarities were connected with the properties of the copolymer chain.
Keywords: Mixed surface layers; Copolymer surfactant mixture; Dodecyltrimethylammonium Bromide; Profile analysis tensiometry; Viscoelasticity;

The study of thiophene adsorption onto La(III)-exchanged zeolite NaY by FT-IR spectroscopy by Fuping Tian; Weicheng Wu; Zongxuan Jiang; Changhai Liang; Yongxing Yang; Pinliang Ying; Xiuping Sun; Tianxi Cai; Can Li (395-401).
Zeolites NaY and LaNaY (ion-exchanged with aqueous lanthanum nitrate solution) were used as adsorbents for removing organic sulfur compounds from model gasoline solutions (without and with toluene) and fluid catalytic cracked gasoline in fixed-bed adsorption equipment at room temperature and atmosphere pressure. The adsorptive selectivity for organic sulfur compounds was significantly increased when Na+ ions in zeolite NaY were exchanged with lanthanum ions. IR spectra of thiophene adsorption indicate that thiophene is adsorbed onto La3+ ions via direct S–La3+ interaction and Na+ ions via π-electronic interaction for La3+-exchanged zeolite NaY, but only via π-electronic interaction with Na+ ions for NaY. The amount of adsorbed thiophene on La3+-exchanged zeolite Y was slightly decreased by coadsorption of benzene, but greatly reduced on NaY. The adsorption of thiophene via interaction with La3+ on La3+-exchanged zeolite Y is hardly replaced by benzene coadsorption. The direct S–La3+ interaction might be the essential reason for the evidently improved adsorptive selectivity of LaNaY for removing organic sulfur compounds from solutions containing large amount of aromatics.The introduction of lanthanum ions into zeolite Y by aqueous ion exchange greatly improves the adsorption selectivity of organic sulfur compounds in solutions containing aromatics because of the direct interaction of adsorbed thiophene with La3+ ions via S atoms.
Keywords: Adsorption; Desulfurization; Thiophene; Aromatics; IR spectra; Gasoline; La3+-exchanged zeolite;

Sorption of palladium(II), rhodium(III), and platinum(IV) on Fe3O4 nanoparticles by Abdusalam Uheida; Mònica Iglesias; Clàudia Fontàs; Manuela Hidalgo; Victòria Salvadó; Yu Zhang; Mamoun Muhammed (402-408).
The adsorption of palladium(II), rhodium(III), and platinum(IV) from diluted hydrochloric acid solutions onto Fe3O4 nanoparticles has been investigated. The parameters studied include the contact time and the concentrations of metals and other solutes such as H+ and chloride. The equilibrium time was reached in less than 20 min for all metals. The maximum loading capacity of Fe3O4 nanoparticles for Pd(II), Rh(III), and Pt(IV) was determined to be 0.103, 0.149, and 0.068 mmol g−1, respectively. A sorption mechanism for Pd(II), Rh(III), and Pt(IV) has been proposed and their conditional adsorption equilibrium constants have been determined to be log K = 1.72 , 1.69, and 1.84, respectively. Different compositions of eluting solution were tested for the recovery of Pt(IV), Pd(II), and Rh(III) from Fe3O4 nanoparticles. It was found that 0.5 mol L−1 HNO3 can elute all of the metal ions simultaneously, while 1 mol L−1 NaHSO3 was an effective eluting solution for Rh(III), and 0.5 mol L−1 NaClO4 for Pt(IV). In competitive adsorption, the nanoparticles showed stronger affinity for Rh(III) than for Pd(II) and Pt(IV).
Keywords: Adsorption; Magnetite; Platinum group metals; Nanoparticles;

Simultaneous adsorption at the liquid/solid and liquid/gas interfaces by Grit Kalies; Steffen Arnrich; Rico Rockmann; Peter Bräuer (409-418).
Physical adsorption from binary or higher-order liquid mixtures on solids is often accompanied by adsorption phenomena at the liquid/gas interface. As long as the adsorption effects are comparable, both interfaces have to be included in the respective thermodynamic equations. A purely phenomenological thermodynamic description in terms of excess quantities is given of the simultaneous adsorption from multicomponent liquid mixtures at the liquid/solid and liquid/gas interfaces. In order to illustrate the thermodynamic procedure, the individual and simultaneous adsorption excess isotherms of three binary liquid mixtures at the liquid/Teflon and liquid/vapor interfaces are calculated from experimental surface-tension and contact-angle data taken from the literature. Special attention is focused on the estimation of error in calculated adsorption isotherms. A line of approach is given to find the confidence limits of adsorption isotherms that cover the entire mole fraction scale. The isotherms as well as their confidence limits are presented and discussed.A phenomenological thermodynamic description is given of the simultaneous adsorption from multicomponent liquid mixtures at the liquid/solid and liquid/gas interfaces. Special attention is focused on the estimation of error in calculated adsorption isotherms.
Keywords: Simultaneous adsorption; Liquid/solid and liquid/gas interfaces; Calculation; Multicomponent liquid mixtures;

The adsorption of a series of aromatic carboxylic acids, with different numbers and positions of carboxyl groups in the phenyl ring, on aluminum hydroxide was investigated with ATR-FTIR and kinetic analyses to verify the role of aromatic carboxyl groups in the surface complexation of NOM with aluminum hydroxide. It was revealed that the formation of outer-sphere complexes dominated the adsorption of most of the aromatic carboxylates over the pH range examined in this study. Inner-sphere complexes were only detected at some pH levels for some aromatic carboxylates adsorption. The aromatic carboxylates were most likely to be adsorbed onto the first surface layer of hydroxyl groups and water molecules without forming coordinative bonds with the aluminum hydroxide surfaces, but strong hydrogen bonds were formed in this process. The adsorption data fitted the pseudo-second-order kinetic model very well. The activation energies of adsorption calculated from the rate constants of pseudo-second-order kinetics agreed with the ATR-FTIR analysis that the aromatic carboxylates, except pyromellitate, were adsorbed predominantly as outer-sphere complexes on aluminum hydroxide at pH 7. This study revealed that phenolic groups may be more significant than carboxylic groups for the chemical adsorption of NOM onto minerals. The presence of additional carboxylic groups enhanced the adsorption considerably, while the enhancement was limited when there were three or four carboxylic groups on the phenyl ring. The adsorption of aromatic carboxylates was affected by the positions and pK a values of the donor groups and the solution pH.Structures of the aromatic carboxylic acids employed in this study.
Keywords: Adsorption; Aluminum hydroxide; Aromatic carboxylate; Enhanced coagulation; Natural organic matter; Surface complexation;

Adsorption of poly(ethylene oxide) at the air/water interface: A dynamic and static surface tension study by Tibor Gilányi; Imre Varga; Magdolna Gilányi; Róbert Mészáros (428-435).
The adsorption of polyethylene oxide (PEO) homologues in a wide range of molecular weight (from M PEO = 200 to 106) at the air/aqueous solution interface was investigated by dynamic and static surface tension measurements. An approximate estimate for the lower limit of PEO concentration was given at which reliable equilibrium surface tension can be determined from static surface tension measurements. It was shown that the observed jump in the earlier published σ – lg ( c PEO ) curves is attributable to the nonequilibrium surface tension values at low PEO concentrations. The adsorption behavior of short chain PEO molecules ( M PEO ⩽ 1000 ) is similar to that of the ordinary surfactants. The estimated standard free energy of PEO adsorption, Δ G 0 , increases linearly with the PEO molecular weight until M PEO = 1000 . In this molecular weight range, Δ G 0 was found to be approximately the fifth of the hydrophobic driving force related to the adsorption of a surfactant with the same number of methylene groups. In the case of the longer chain PEOs the driving force of adsorption is so high that the adsorption isotherm is near saturation in the experimentally available polymer concentration range. Above a critical molecular weight the PEO adsorption reveals universal features, e.g., the surface tension and the surface density of segments do not depend on the polymer molecular weight.The observed upturn in the earlier published σ – lg ( c PEO ) curves is shown to be attributable to the nonequilibrium surface tension values at low PEO concentrations.
Keywords: Polymer adsorption; Fluid/fluid interface; Equilibration criteria; Macromolecule; Surface tension; Adsorption driving force;

The rate of dye adsorption from aqueous effluents onto palm kernel shell (PKS) activated carbon has been studied experimentally using the batch adsorption method. The adsorption rates of methylene blue on PKS for systems of different initial dye concentrations are modeled using a film-pore-concentration dependent surface diffusion (FPCDSD) model. The FPCDSD model is sufficiently general and can be reduced easily to describe other simplified models. Using the FPCDSD model, only a single set of mass transfer parameters is required to describe the methylene blue/PKS system for different initial concentrations. A different set of mass transfer parameters are needed to obtain the best fitting if the pore diffusion is not included in the model.The film-pore-concentration dependent surface diffusion (FPCDSD) model is able to describe the Methylene Blue/PKS system using a single set of mass transfer parameters for a wide range of different initial concentrations.
Keywords: Dye; Adsorption; Diffusion; Activated carbon; Palm kernel shell;

Monolayers of giant, tripod-shaped molecules 1 with each tripod leg composed of seven phenylene units end-capped with a triallylsilyl group were prepared on hydrogen-terminated silicon surfaces (H–Si(111)) via thermally induced surface hydrosilylation. The films were characterized by ellipsometry, contact-angle goniometry, and X-ray photoelectron spectroscopy (XPS). The measured ellipsometric thickness of 24 Å of the films suggests anchoring of 1 on the substrate surface with a tripod orientation of high coverage. By measuring the contact angle hysteresis of a series of probe liquids with systematically varied sizes, the molecular pores present on the films consisting of the intercalated molecules of 1 are similar to the cross sectional areas of glycerol and decalin of 0.32–0.49 nm2. Finally, as evidenced by XPS, excellent yields ( ∼ 90 % ) of Suzuki coupling reactions with arylboronic acid derivatives on the films was achieved, suggesting that the desired tripod orientation of such giant molecules as 1 helps to eliminate the steric hindrance for the reaction.
Keywords: Tripod films; Hydrogen-terminated silicon surfaces; Suzuki coupling reactions; Thermally induced surface hydrosilylation; X-ray photoelectron spectroscopy;

In a binary system the sorption of Na+ and Ca2+ by kraft pulps follows a second order kinetics, and the isotherms follow the Langmuir model. The sorption capacity is dependent on pH and temperature. The thermodynamic parameters indicate that the sorption is exothermic and spontaneous. In a single-component system, the sorption capacity of the kraft pulp for Na+ and Ca2+ increases with the degree of dissociation of ionisable cellulosic components of the kraft pulp fibres. In a binary system the exchange of Na+ and Ca2+ is highly dependent on pH. SEM and X-ray analysis indicated that at pH above 11.0 calcium forms a precipitate bound to the surface of the fibres.Ca2+ has a much higher sorption affinity than Na+ in the binary systems. It is evident that Ca2+ forms precipitate and possible ionic pairs of monovalence at high pH.
Keywords: Electrokinetic; Fiber charge; Sorption; Kraft pulps; SEM;

Thermodynamic assessment of Hg(II)–gibbsite interactions by Rohan Weerasooriya; Wasana Seneviratne; Heasha A. Kathriarachchi; Heinz J. Tobschall (452-460).
As discrete particles and/or as surface coatings on other minerals in natural systems, aluminum hydroxides are efficient sinks for Hg(II). The Hg(II) adsorption on gibbsite was determined as a function of temperature (T), pH, and the type of background electrolytes, i.e., NaNO3, NaClO4, and NaCl. When the equilibration time t E ∼ 2  h , the Hg(II) retention on gibbsite was found to be a reversible process, which was ascribed to adsorption. The Hg(II) adsorption capacity, i.e., Γ Hg ( II ) , varied with the type of electrolyte used in accordance with the following order: Γ Hg ( II ) NO 3 ⩾ Γ Hg ( II ) ClO 4 > Γ Hg ( II ) Cl . In all cases, the estimated thermodynamic parameters showed that the Hg(II) adsorption on gibbsite was endothermic and spontaneous. The Hg(II) adsorption data were quantified with the Langmuir or Hill, and Dublin–Radushkevick (DR), isotherms at all temperatures and acidity levels examined. Always, the Hg(II) adsorption data were in compliance with the DR model. However, the Hg(II) adsorption in NaNO3 or NaClO4 was interpreted in terms of the Langmuir model. When NaCl was used as electrolyte, the Hg(II) adsorption was modeled well with the Hill equation. The mean free energy values calculated from DR plots concluded that Hg(II)–gibbsite interactions are a result of chemical bonding.As discrete particles and/or as surface coatings on other minerals in natural systems, aluminum hydroxide are efficient sinks for Hg(II). The Hg(II) adsorption on gibbsite was determined as a function of temperature (T), pH and the type of background electrolytes, i.e. NaNO3, NaClO4, and NaCl. At short time periods of equilibration the Hg(II) retention on gibbsite was reversible. The Hg(II) adsorption capacity, i.e. Γ Hg ( II ) varied with the type of electrolyte used. Estimated thermodynamic parameters of Hg(II) adsorption show that the overall adsorption was endothermic and spontaneous. As shown in the figure for chemical data in NaClO4 (similar results were obtained in NaCl, and NaNO3) always Hg(II) adsorption on gibbsite was in compliance with Dublin–Radushkevick (DR) model. From the DR plots apparent free energy of adsorption, E, was also calculated. It was shown that E was a function of the background electrolyte and the system pH. In most cases, the E pH 4 < E pH 8 showing a comparably strong Hg(II) bonding at alkaline pH. Always the E values ranged between 7 and 22 kJ mol−1 indicating chemical bonding of Hg(II) adsorption on gibbsite.
Keywords: Hg(II); Langmuir isotherm; Hill isotherm; Dubinin–Radushkevick (DR) isotherm; Gibbsite;

Arrays of lipid bilayers and liposomes on patterned polyelectrolyte templates by Neeraj Kohli; Sachin Vaidya; Robert Y. Ofoli; Robert M. Worden; Ilsoon Lee (461-469).
This paper presents novel methods to produce arrays of lipid bilayers and liposomes on patterned polyelectrolyte multilayers. We created the arrays by exposing patterns of poly(dimethyldiallylammonium chloride) (PDAC), polyethylene glycol (m-dPEG) acid, and poly(allylamine hydrochloride) (PAH) on polyelectrolyte multilayers (PEMs) to liposomes of various compositions. The resulting interfaces were characterized by total internal reflection fluorescence microscopy (TIRFM), fluorescence recovery after pattern photobleaching (FRAPP), quartz crystal microbalance (QCM), and fluorescence microscopy. Liposomes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dioleoyl-sn-glycero-3-phosphate (monosodium salt) (DOPA) were found to preferentially adsorb on PDAC and PAH surfaces. On the other hand, liposome adsorption on sulfonated poly(styrene) (SPS) surfaces was minimal, due to electrostatic repulsion between the negatively charged liposomes and the SPS-coated surface. Surfaces coated with m-dPEG acid were also found to resist liposome adsorption. We exploited these results to create arrays of lipid bilayers by exposing PDAC, PAH and m-dPEG patterned substrates to DOPA/DOPC vesicles of various compositions. The patterned substrates were created by stamping PDAC (or PAH) on SPS-topped multilayers, and m-dPEG acid on PDAC-topped multilayers, respectively. This technique can be used to produce functional biomimetic interfaces for potential applications in biosensors and biocatalysis, for creating arrays that could be used for high-throughput screening of compounds that interact with cell membranes, and for probing, and possibly controlling, interactions between living cells and synthetic membranes.Novel approaches for fabricating arrays of lipid bilayers and liposomes on patterned polyelectrolyte multilayers are presented.
Keywords: Polyelectrolytes; Liposomes; Lipid bilayers; BLM; Total internal reflection fluorescence microscopy (TIRFM); Fluorescence recovery after pattern photobleaching (FRAPP); Quartz crystal microbalance (QCM); Fluorescence microscopy; Microarray;

Silica/polypyrrole (PPY) core/shell microspheres and PPY hollow microspheres were prepared by the template of silica particles whose surface character was modified with different modified agents. The morphology and structure of the particles were characterized by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Elemental analysis and X-ray photoelectron spectroscopy (XPS) were carried out to characterize the structure of PPY hollow microspheres. We investigated the effect of different modified agents on the surface character of silica particles and the effect of surface character of silica particles on the morphology of PPY hollow microspheres. The effect of reaction conditions on the size of core/shell particles and hollow particles was also studied.We used different modified agents with surface activity to modify the surface character of silica particles and then used these silica particles as the template to prepare the silica/PPY core/shell particles and PPY hollow particles.
Keywords: Uniform; Core/shell microspheres; Hollow; Polypyrrole; Modified agents;

Novel adsorbent based on silkworm chrysalides for removal of heavy metals from wastewaters by Alexandre T. Paulino; Flavienne A.S. Minasse; Marcos R. Guilherme; Adriano V. Reis; Edvani C. Muniz; Jorge Nozaki (479-487).
In this contribution, maximum capacity for adsorption of Pb2+, Ni2+, and Cu2+ by silkworm chrysalides (SC) was determined. The raw silkworm chrysalides (SCr) and chrysalides after acidic washing (SCw) were used. Chitin (CT), extracted from SC, and chitosan (CS), with 85% deacetylation, were employed as reference samples. Adsorption tests showed that all the studied adsorbents exhibited excellent performance in removal of metals. The choice of a more appropriate adsorbent is related to its efficiency for removal of a specific metal. The studied materials presented different intensities for metal adsorption as follows: (i) Ni2+  > Cu2+  > Pb2+ for SCr; (ii) Pb2+  > Cu2+  > Ni2+ for SCw; (iii) Ni2+  > Cu2+  > Pb2+ for CT; and (iv) Cu2+  > Pb2+  > Ni2+ for CS. Metal adsorption onto SCr and CS was analyzed by Freundlich and Langmuir isotherm equations. Adsorption values for CS–Pb and SCr–Ni were provided by the Freundlich model, while the adsorption values for CS–Cu, CS–Ni, SCr–Pb, and SCr–Cu were provided by the Langmuir model. The studied adsorbents are suitable for use in treatment of wastewater. From the economic point of view, the use of SCr as an adsorbent of heavy metals (mainly Ni2+) on the large industrial scale would be more appropriate.Maximum capacity of raw silkworm chrysalides (SCr) for adsorption of Pb2+, Ni2+, and Cu2+ was determined. Adsorption tests indicated that SCr exhibited excellent performance in removal of metals (mainly Ni2+).
Keywords: Adsorption; Raw silkworm chrysalides; Chitosan; Chitin; Heavy metals; Wastewater;

Temperature dependence of thermodynamic activity in volatile anesthetics: Correlation between anesthetic potency and activity by Yasushi Yamamoto; Keijiro Taga; Tadayoshi Yoshida; Hiroshi Kamaya; Issaku Ueda (488-492).
Temperature dependence of the saturated concentration and the activity coefficient of anesthetics (1-propanol, diethyl ether, chloroform, and halothane) in water were evaluated using vapor pressure and H NMR measurement. We found that these physical values (quantities) correlate with anesthetic potencies estimated according to the thermodynamic equilibrium model. The anesthetic potency for hydrophilic anesthetic (diethyl ether) decreased with decreasing temperature because of the temperature specificity of this saturated concentration. In contrast, potencies of hydrophobic anesthetics (chloroform and halothane) increased with decreasing temperature because of the temperature specificity of those activity coefficients. By assuming that anesthetics interact with hydrated water of cell membranes, the temperature dependence of anesthetic potencies in vivo is qualitatively explicable.Temperature dependence of the activity coefficient γ w of anesthetics in water in the vicinity of clinical concentration. The relative temperature on the horizontal axis indicates the ratio of the solution temperature and the boiling point of anesthetics. The asterisk indicates γ w at the relative temperature corresponding to a body temperature of 37 °C. Circles: 1-propanol (278 mM); triangles: diethyl ether (28 mM); diamonds: chloroform (2.8 mM); squares: halothane (2.8 mM). Each concentration without 1-propanol is much smaller than each saturated concentration.
Keywords: Saturated concentration; Activity coefficient; Thermodynamic activity; Hydrated water; Anesthetic potency; Hydrophilic and hydrophobic anesthetics;

A thermodynamic study of GPI-anchored and soluble form of alkaline phosphatase films at the air–water interface by Frédéric Ronzon; Jean-Paul Rieu; Jean-Paul Chauvet; Bernard Roux (493-502).
Glycosylphosphatidyl inositol (GPI) anchored proteins are localized and clustered on the outer layer of the plasma membranes forming microdomains. Among them, mammalian alkaline phosphatases (AP-GPI) are widely distributed enzymes. They can also exist as soluble proteins without anchor (APs). Using the Langmuir film technique, we study the thermodynamic properties of monolayers for both protein forms at the air–buffer interface. The enzymatic activity is maintained at the interface but the adsorption of the two forms of AP is very different. AP-GPI presents a higher surface activity and a larger molecular area than the soluble form. The molecular area deduced for high surface pressures suggests a different organization of the monolayers for these two forms. APs molecules seem to adsorb as a multilayer at the interface while AP-GPI appear to be orientated with the major axis parallel to the interface. This orientation allows the accessibility of AP-GPI enzymatic sites that are turned in direction of the subphase as in vivo where the active sites must be turned outside of the membrane.
Keywords: Lipidic anchors; Alkaline phosphatase; Enzyme adsorption; Langmuir films; 2D thermodynamics;

PbS nanostructures with different morphologies, such as rod-like, belt-like, downy-velvet-flower-like and dendrite-like, were fabricated successfully under varied reaction conditions in aqueous solution at lower temperature by the assistance of surfactant CTAB. Especially, among all the synthesis methods for PbS nanocrystals, this is the first report using basic acetate of lead, which was formed at initial reaction stage, as a precursor to control the crystal nucleation rate. This synthesis method is a promising one to metal sulfide for its easy control, low-cost and large-scale production. X-ray powder diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), field-emission scanning electron microscopy (FE-SEM) and UV–visible spectrophotometer (UV–vis) were used to characterize the products. A rational mechanism is proposed and three control factors to the crystal directional growth are also concluded.PbS nanostructures with different morphologies, such as rod-like, belt-like, downy-velvet-flower-like and dendrite-like, were fabricated successfully under varied reaction conditions in aqueous solution at lower temperature by the assistance of surfactant CTAB.
Keywords: PbS; Nanorod; Nanobelt; Nanodendrite; Nanodowny-velvet-flower;

AFM colloidal forces measured between microscopic probes and flat substrates in nanoparticle suspensions by J. Drelich; J. Long; Z. Xu; J. Masliyah; J. Nalaskowski; R. Beauchamp; Y. Liu (511-522).
Colloidal forces between atomic force microscopy probes of 0.12 and 0.58 N/m spring constant and flat substrates in nanoparticle suspensions were measured. Silicon nitride tips and glass spheres with a diameter of 5 and 15 μm were used as the probes whereas mica and silicon wafer were used as substrates. Aqueous suspensions were made of 5–80 nm alumina and 10 nm silica particles. Oscillatory force profiles were obtained using atomic force microscope. This finding indicates that the nanoparticles remain to be stratified in the intervening liquid films between the probe and substrate during the force measurements. Such structural effects were manifested for systems featuring attractive and weak repulsive interactions of nanoparticles with the probe and substrate. Oscillation of the structural forces shows a periodicity close to the size of nanoparticles in the suspension. When the nanoparticles are oppositely charged to the probes, they tend to coat the probes and hinder probe–substrate contact.
Keywords: Colloidal forces; Nanofluid; Nanoparticles; Structural forces; Suspensions;

Zinc sulfate is a well-known selective depressant for zinc sulfide minerals such as sphalerite during the flotation of complex Cu–Pb–Zn sulfide ores. It deactivates sphalerite flotation by substituting the activating metal ions, and depresses sphalerite flotation by forming hydrophilic coatings of zinc hydroxyl species on sphalerite surfaces. However, we recently observed that zinc sulfate could also induce coagulation of fine sphalerite particles and such coagulation significantly reduced the mechanical entrainment of the fine sphalerite. Therefore, it seems that the effectiveness of zinc sulfate as a selective sphalerite depressant is not only due to its ability to make mineral surface hydrophilic, which reduces genuine flotation, but also due to its ability to coagulate the mineral, which reduces mechanical entrainment. Zinc sulfate is a “dual function” selective flotation depressant.Mechanical entrainment of sphalerite in froth flotation is dramatically reduced when the fine particles of sphalerite are aggregated by zinc sulfate.
Keywords: Froth flotation; Mechanical entrainment; Zinc sulfate; Depression; Coagulation; Sulfide minerals;

Probing particle size distributions in natural surface waters from 15 nm to 2 μm by a combination of LIBD and single-particle counting by Clemens Walther; Sebastian Büchner; Montserrat Filella; Vincent Chanudet (532-537).
We present a technique for measuring colloid size distributions between 15 nm and 2 μm at concentrations relevant to natural surface waters. Two particle-measuring methods are combined: laser-induced breakdown detection (LIBD), which allows the quantification of colloid size distributions below 400 nm, and a commercial single-particle counter that extends the accessible size range up to two μm. Centrifugation was used in order to separate micrometer sized particles for the LIBD measurement. The feasibility is demonstrated on water of Lake Brienz (Switzerland) and the River Pfinz (Germany) and the particle size distributions follow Pareto's law even down to 15 nm in both cases.Colloid size distributions from 15 nm to 2 μm are measured directly in solution at trace concentrations by combining LIBD and a SPC.
Keywords: Colloid; Breakdown; Particle size distribution; LIBD; SPC; Fresh waters;

High ionic strength electrokinetics of melamine–formaldehyde latex by Marek Kosmulski; Per Dahlsten; Piotr Próchniak; Jarl B. Rosenholm (538-541).
The electrokinetic potential of melamine–formaldehyde latex at high ionic strengths was measured by means of two different instruments. The present study confirms that the ζ potentials in 1 M 1–1 electrolyte solutions can be as high as ±20 mV. The IEP of latex at low ionic strengths was at pH 11. The increase in the electrolyte concentration induced a shift in the IEP to low pH for all studied salts, and this indicates specific adsorption of the anions. The magnitude of the shift depends chiefly on the nature of the anion and increases in the series Cl < NO 3 = Br < I , and the nature of the cation (Li, Na, K, Cs) plays a rather insignificant role.
Keywords: Zeta potential; Isoelectric point; Latex; Ionic strength; HSAB principle;

Nanoscale electrostatic actuators in liquid electrolytes by James G. Boyd; Doyoung Kim (542-548).
Equilibrium and energy analyses were performed for an electrostatic actuator consisting of two plane parallel electrodes, operated using DC voltages, separated by a liquid electrolyte. One electrode is fixed, and the other electrode is connected to a spring and is free to move. The mechanical equilibrium includes the spring force, the van der Waals force, and the electrochemical force as given by the solution of the linearized Poisson–Boltzmann equation. The electrode separation is determined as a function of the applied potential, the natural (i.e., zeta) potential, the Debeye length, the initial electrode separation, the spring constant, and the Hamaker constant. The actuator exhibits the classical “pull-in” instability. The natural potential increases the critical applied potential but does not significantly affect the critical separation. For zero natural potential, the spring constant does not affect the critical separation. Ratios of the maximum spring energy, the maximum van der Waals energy, and the maximum electrochemical energy were plotted as functions of the Hamaker constant and the initial electrode separation.An electrostatic actuator in a liquid electrolyte is modeled. The electrode separation is determined as a function of the applied potential, the natural (i.e., zeta) potential, the Debeye length, the initial electrode separation, the spring constant, and the Hamaker constant.
Keywords: Electrostatic actuator; Instability; Energy; Debeye length; Hamaker constant;

Visualization study on sedimentation of micron iron oxide particles by Jin-Fang Chen; Ye Luo; Jun-Hui Xu; Qi-Ming Chen; Jia Guo (549-553).
In this paper, a novel technique combined light-electronic microscopy and computer imaging trace was used for visualization of the sedimentation of micron iron oxide particles in a customized micro-reactor. Micron iron oxide particles were recovered from the cinder of sulfuric acid production by sedimentation separating and hydraulic rating. Effects of particle size, shape and surface roughness on the sedimentation velocity were investigated. For irregular-shape particles, the sedimentation velocity and the geometric parameters of the particles were measured by the imaging trace technique. A correction coefficient (c) was used to modify the Stokes equation. In this study, the relationship between the correction coefficient and the equivalent diameter ( d p ) was found to be linear: c = 0.6272 − 0.0298 d p , for iron oxide particles with equivalent diameter 4–22 μm.The iron oxide particles used in this study were cinders of the sulfuric acid production from ChuXing Co. Ltd., Hubei Province, China, by sedimentation separating and hydraulic rating. Added some water in a micro-reactor and then dispersed a small amount of iron oxide particles (the solid to liquid ratio is 0.01%, by weight) into the reactor. The optical micrograph of the particles prior to suspension into the liquid is shown in the figure.
Keywords: Iron oxide particles; Sedimentation; Micro-reactor; Visualization; Stokes equation;

Sulfate-supported iron–chromium mixed oxide pillared clay was prepared varying the sulfate loading from 1 to 5 wt% by the incipient wetness method and characterized by low-angle XRD, BET surface area, and ammonia TPD. All the samples were found to be stable up to 500 °C having the basal spacing ⩾17.7 Å even after sulfate impregnation. Formation of strong Lewis acid sites and decrease in the number of Brønsted acid sites due to the sulfate loading were observed from the ammonia TPD curve. Catalytic properties of the sulfated materials were evaluated with the help of methanol conversion and aromatic alkylation reactions and correlated with the surface area and TPD results. For methanol conversion, decomposition product selectivity increases due to the sulfate addition. A negligible decrease in the surface area and a substantial increase in the catalytic activity were observed due to the sulfate loading of 1–2 wt%. However, a significant decrease in the surface area as well as catalytic activity was observed for the 3 wt% and above sulfate loaded samples which may be due to the partial blockage of pores by excess sulfate. Results shows the importance of acidity of the material due to sulfate loading (up to 2 wt%) and thus can be used as a better acid catalyst.Acidity of the Fe–Cr pillared clay can be increased by addition of 2 wt% sulfate so that the material can be used as alkylation catalyst.
Keywords: Sulfated; Iron–chromium mixed oxide pillared clay; Methanol; Alkylation;

The effect of pH on retention of 56Mn produced by the ( n , γ ) process in lanthanum and strontium permanganates has been investigated. It has been observed that the retention is apparently pH-independent over the pH range from 2.5 to 9.0; however, a pronounced effect was seen in low (pH 1.0–2.0)- and high (pH 9.5–12.5)-pH regions for both solid and solution phase irradiated samples. The results obtained are discussed in the light of existing ideas, which would be of help for a better understanding of the chemical stabilization of the recoil 56Mn atom and its subsequent participation, with reactive intermediates thus helping in the mechanism of recoil chemical stabilization of 56Mn in lanthanum and strontium permanganates.It is clear from the curves that retention is apparently independent over a wide pH range (∼2.0–10.0), but increases at both high and low pH for both states of irradiation are shown in the figure.
Keywords: Recoil; Retention; pH-dependence study; MnO 4; Radiocolloidal; Chemical stabilization; Hydrolysis;

Enhanced nucleophilic reactivity of hydroxamate ions in some novel micellar systems for the cleavage of Parathion by Kallol K. Ghosh; Daliya Sinha; Manmohan L. Satnami; D.K. Dubey; A. Shrivastava; Rama M. Palepu; P.R. Dafonte (564-568).
The reactivity of three α-nucleophiles, i.e. N-phenylbenzohydroxamate, benzohydroxamate and salicylhydroxamate ions towards cleavage of p-nitrophenyldiethyl phosphorothioate (Parathion) is considerably enhanced in the presence of cationic surfactant, i.e. cetyltrimethylammonium bromide. The esterolytic properties of N-phenylbenzohydroxamate ion for parathion have also been examined in two novel surfactants, viz. cetyltriphenylphosphonium bromide and cetyldimethyl ethanol ammonium bromide. The cetyldimethyl ethanol ammonium bromide is more reactive. The rate–surfactant profiles have been fitted with pseudophase model.
Keywords: Nucleophilic reactivity; Hydroxamate ions; Novel surfactants; Parathion;

Hydrotalcite-like compounds (HTlcs) containing Mg2+, Al3+, and Ce3+ in the hydroxide layer and with carbonate as charge-balancing anion have been prepared by a co-precipitation (at constant pH) method. The Al/Ce ratio in the final product depends on the concentration in the initial solution. The crystallinity of the layered materials decreases with the increase in cerium content, probably, due to the distortions introduced by the large difference in the ionic radii of the cations. All the synthesized materials were characterized by XRD, FT-IR spectroscopy and TG/DTA. The textural properties were determined from low-temperature nitrogen adsorption–desorption measurements.From the TG/DTA pattern of the various wt% of Ce containing Mg/Al HTlcs it is observed that the weight loss takes place in two different stages corresponding to two endotherms in the DTA pattern.
Keywords: HTlcs; Co-precipitation; XRD; TG/DTA; N2 adsorption–desorption studies; Memory effect;

The alumina ceramic membrane has been modified by the addition of palladium in order to improve the H2 permeability and selectivity. Palladium-alumina ceramic membrane was prepared via a sol–gel method and subjected to thermal treatment in the temperature range 500–1100 °C. Fractal analysis from nitrogen adsorption isotherm is used to study the pore surface roughness of palladium-alumina ceramic membrane with different chemical composition (nitric acid, PVA and palladium) and calcinations process in terms of surface fractal dimension, D. Frenkel–Halsey–Hill (FHH) model was used to determine the D value of palladium-alumina membrane. Following FHH model, the D value of palladium-alumina membrane increased as the calcinations temperature increased from 500 to 700 °C but decreased after calcined at 900 and 1100 °C. With increasing palladium concentration from 0.5 g Pd/100 ml H2O to 2 g Pd/100 ml H2O, D value of membrane decreased, indicating to the smoother surface. Addition of higher amount of PVA and palladium reduced the surface fractal of the membrane due to the heterogeneous distribution of pores. However, the D value increased when nitric acid concentration was increased from 1 to 15 M. The effect of calcinations temperature, PVA ratio, palladium and acid concentration on membrane surface area, pore size and pore distribution also studied.Fractal analysis from nitrogen adsorption isotherm is used to study the pore surface roughness of palladium-alumina ceramic membrane in term of surface fractal dimension, D. Frenkel–Halsey–Hill (FHH) model was used to determine the surface fractal dimension of palladium-alumina membrane.
Keywords: Palladium-alumina membrane; Surface fractal dimension; Surface roughness; Nitrogen adsorption isotherms; Sol–gel;

Characterization of Langmuir and Langmuir–Blodgett films of a thiomacrocyclic ionophore by surface pressure and AFM by J. Torrent-Burgués; M. Pla; L. Escriche; J. Casabó; A. Errachid; F. Sanz (585-593).
The new synthesized thiomacrocyclic ionophore 4-phenyl-4-sulfide-11-(1-oxodecyl)-1,7-dithia-11-aza-4-phosphacyclotetradecane has proven to form Langmuir and Langmuir–Blodgett (LB) films. This ionophore shows a large affinity for copper(II) ions. Thus, the influence of the subphase composition on the surface pressure–area isotherms has been studied. The LB films have been observed by AFM and the effect of the subphase composition and the deposition surface pressure on the LB films is discussed. AFM image morphology has been correlated to the ionophore molecular structure. Surface pressure–area isotherms and AFM images show that the presence of copper(II) ions has an important role in the film structure.Langmuir and Langmuir–Blodgett films of a new synthesized thiomacrocyclic compound have been characterized using surface pressure–area isotherms and AFM. The copper ions play an important role in the film structure.
Keywords: Langmuir film; Langmuir–Blodgett film; Thiomacrocyclic ionophore; AFM;

Collisions of liquid coated solid spherical particles in a viscous fluid by O.K. Matar; P.D.M. Spelt; F. Stepanek (594-606).
An analytical description is presented for the head-on collision of two spherical rigid particles that are coated with a thin layer of one liquid and immersed in another. Lubrication theory is used to resolve the spatio-temporal evolution of the coating surfaces, in conjunction with the fluid flow in the gap region between the particles. The analysis is carried out up to the point where the gap region has almost completely been drained; intermolecular forces are neglected. The effects of particle inertia, the ratio of particle radii, surface tension, and the viscosity ratio of the coating and carrier fluids are studied; these are parameterised by St, β, Ca and m, respectively. The results of the present work elucidate the effect of the above-mentioned factors on the conditions under which particles rebound (assumed to occur if the distance between the particles becomes very short while the relative velocity does not vanish) or stick. In particular, summarizing flowmaps show that the likelihood of particles rebounding increases with increasing St and decreasing β, Ca and m. On the other hand, it is shown that the force on approaching particles depends on all of these parameters in a non-monotonic manner.Schematic representation of two pre-coated spherical solid particles undergoing a normal collision in a viscous fluid.
Keywords: Collisions; Particles; Coating; Interface; Surface tension; Lubrication; Thin film; Capillarity;

Surface properties of inclusion complexes between α-cyclodextrin and poly(ethylene oxide) by Ligia Gargallo; Danitza Vargas; Angel Leiva; Deodato Radić (607-611).
The surface properties of the supramolecular inclusion complex (IC) obtained from the threading of α-cyclodextrin (α-CD) onto poly(ethylene oxide) (PEO) free in solution are studied. The complexes were characterized by IR, 1H NMR spectroscopy, and thermal analysis. The variation of the interfacial tension, γ int , with inclusion complex (IC) concentration and temperature were determined. The results were compared with those found for PEO under the same conditions. α-CD does not present surface activity. To quantify the adsorption process of IC and PEO in aqueous medium, the Gibbs equation was used. The driving force for adsorption of IC at the air/aqueous interface seems to arise from an enthalpic contribution. The wettability of the α-CD, PEO, and IC films with two liquids was determined by static contact angle measurements. The hydrophobicity degree was estimated. IC is more hydrophobic than PEO and α-CD.The driving force for adsorption of inclusion complex between α-cyclodextrin and poly(ethylene oxide) at the air/aqueous interface seems to arise from an enthalpic contribution.
Keywords: Adsorption layers; Inclusion complex; α-Cyclodextrin; Hydrophobicity; Surface activity;

Microregion detection of ionic liquid microemulsions by Yanan Gao; Suqing Wang; Liqiang Zheng; Shuaibing Han; Xuan Zhang; Deming Lu; Li Yu; Yongqiang Ji; Gaoyong Zhang (612-616).
Nonaqueous ionic liquid (IL) microemulsion consisting of IL, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), surfactant TX-100, and toluene was prepared and the phase behavior of the ternary system was investigated. Electrical conductivity measurement was used for investigating the microregions of the nonaqueous IL microemulsions. On the basis of the percolation theory, the bmimBF4-in-toluene (IL/O), bicontinuous, and toluene-in-bmimBF4 (O/IL) microregions of the microemulsions were successfully identified using insulative toluene as the titration phase. However, this method was invalid when conductive bmimBF4 acted as the titration phase. The microregions obtained by conductivity measurements were further proved by electrochemical cyclic voltammetry experiments. The results indicated that the conductivity method was feasible for identifying microstructures of the nonaqueous IL microemulsions.Nonaqueous ionic liquid microemulsion consisting of 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), TX-100, and toluene were prepared and the phase behavior was investigated. Electrical conductivity was used to identify the microregions of the microemulsion on the basis of percolation theory. The data were further proved by the experiments of cyclic voltammetry.
Keywords: Microemulsion; Ionic liquid; Microstructure; Conductivity; Cyclic voltammetry;

Controlled release from a nanocarrier entrapped within a microcarrier by Edith C. Rojas; Nurettin Sahiner; Louise B. Lawson; Vijay T. John; Kyriakos D. Papadopoulos (617-623).
This study illustrates the entrapment of the dye molecule fluorescein sodium salt (FSS) by hydrogel nanoparticles, which are in turn confined inside a water-in-oil-in-water double-emulsion globule, and its subsequent release by the action of the competing agent hydrochloric acid (HCl). Thus, a “double carrier” concept is being introduced in which a nanoscale delivery vehicle is being transported by a microscale delivery vehicle in order to simultaneously take advantage of both systems. This may facilitate storage and handling while protecting the active substance and improving its action upon application.
Keywords: Multiple emulsion; Double emulsion; Hydrogel nanoparticles; Delivery vehicle; Controlled release;

Ester aminolysis by morpholine in AOT-based water-in-oil microemulsions by L. García-Rio; J.C. Mejuto; M. Pérez-Lorenzo (624-630).
A kinetic study of the aminolysis of p-nitrophenyl acetate (NPA) by morpholine (MOR) in AOT/isooctane/water (w/o) microemulsions was conducted. Based on the solubilities of NPA and MOR in water and isooctane, both compounds partition between the continuous medium, interface and water microdroplets of the microemulsion. Because the rate of the aminolysis reaction decreases with decreasing polarity of the solvent, the reaction must take place to a negligible extent in the continuous medium relative to the interface and the aqueous microdroplets. We used the pseudo-phase model to determine the rate constants at the interface, k 2 i , and in the water microdroplets, k 2 w . Both k 2 i and k 2 w were found to be independent of W in the aminolysis of NPA by MOR. This is a result of the expected increase in k 2 w on decreasing W being offset by the decrease in k 2 i with increase in the water content of the system. Based on the results, the reaction takes place to an extent of only 16% in the water microdroplets at W = 40 , the proportion decreasing with decreasing water content.
Keywords: Microemulsion; Reverse micelle; AOT; Aminolysis; Kinetic; Morpholine;

Interactions between gemini surfactant alkanediyl- α , ω -bis(dodecyldimethylammonium bromide) and polyelectrolyte NaPAA by Yingying Pi; Yazhuo Shang; Changjun Peng; Honglai Liu; Ying Hu; Jianwen Jiang (631-636).
Interactions between cationic gemini surfactant alkanediyl- α , ω -bis(dodecyldimethylammonium bromide) (12-n-12, n = 3 , 4 , 6 ) and oppositely charged polyelectrolyte sodium polyacrylate (NaPAA) in aqueous solution have been investigated by measuring fluorescence, conductivity, UV–vis transmittance, dynamic lighting scattering, and transmission electron microscopy. Micelle-like structure and 12-n-12/NaPAA complex are observed to form due to the electrostatic and hydrophobic interactions, and the effective diameter of the complex reduces with increasing 12-n-12 concentration. The microstructures of 12-n-12/NaPAA solution determined from fluorescence and electron microscopy measurements are in good agreement. The spacer length is found to play an important role in the interactions of 12-n-12 with NaPAA.
Keywords: Gemini surfactant; Polyelectrolyte; Interaction; Microstructure; Spacer length;

Influence of aza crown ethers on the electric percolation of AOT/isooctane/water (w/o) microemulsions by J. Dasilva-Carvalhal; D. Fernández-Gándara; L. García-Río; J.C. Mejuto (637-643).
A study was carried out on the influence of different aza crown ethers on the electric percolation of AOT/isooctane/water microemulsions. A dual behavior of the aza crown ethers with regard to the percolative phenomenon was observed: low additive concentration causes an increase in the percolation temperature, whereas at high additive concentration a reduction in the percolation temperature of the system was observed. This dual behavior allowed us to define the compensation concentration, which corresponds the aza crown ether concentration at which there is no effect on the percolative phenomenon. We observed a correlation between the effect exerted by the aza crown ethers and the size of the cavity. This shows the importance of the capacity to complexate Na+ and solubilize it in the interface and the continuous medium on the electric percolation. We also observed a correlation between the effect of the aza crown ethers on the percolation temperature and their external size. This shows the importance of their inclusion in the interface on the percolative phenomenon. Such an inclusion modifies the properties of the AOT film, facilitating the exchange of matter between droplets. A satisfactory multiparametric correlation between the compensation concentration, the distribution of the aza crown ether between water and 1-octanol, and the number of electron-donor atoms (O and N) in the crown ether was obtained. The effects have been compared with those corresponding to the crown ethers.
Keywords: Microemulsion; Percolation; Crown ether; Electrical conductivity;

Effect of the spacer group of cationic gemini surfactant on microemulsion phase behavior by Lifei Chen; Yazhuo Shang; Honglai Liu; Ying Hu (644-650).
The phase behavior of a system of n-butanol/n-octane/water/cationic gemini surfactant, alkanediyl- α , ω -(dimethydodecyl-ammonium bromide)(12-n-12, n = 3 , 4 , 6 ), has been investigated by determination the pseudo-ternary phase diagrams. The results have shown that the spacer group of gemini surfactant has a great effect on the phase behavior. The longer the spacer group for the geminis, the more similar the geminis properties to the traditional ones. The mixing content of surfactant and cosurfactant needed for forming microemulsions increases with the geminis' spacer group. The study has also shown that the shorter spacer group of geminis is favorable for the formation of higher ordered surfactant aggregates such as liquid crystals. Furthermore, the microstructures of each region for the studied systems have been investigated by electrical conductivity measurements, UV-visible absorbance spectra of pyrene probe, and dynamic light scattering (DLS). All the results are in accord with each other. DLS makes use of the sensitivity of DLS to structural changes and as expected the hydrodynamic diameter of the microemulsion droplet changes as the transformation of microemulsion microstructures take place. Moreover, the spherical and network structures of microemulsion were further verified by freezing-etching TEM.This is one of pseudo-ternary phase diagrams that show the great effect of spacer group of gemini surfactant on the phase behavior of n-butanol/n-octane/water/(12-3(4,6)-12,2Br−1) system and one showing the dots for microstructure of microemulsion determination. And the results obtained from electrical conductivity measurement, TEM, UV-visible absorbance spectra of pyrene probe as well as dynamic light scattering are in accord with each other.
Keywords: Gemini surfactant; Microstructure; Electrical conductivity; UV-visible absorbance; DLS;

The electrophoretic mobility of spherical soft particles in concentrated colloidal suspensions is numerically calculated. The particle is modeled as a hard core coated with an ion-penetrable membrane bearing a uniform distribution of fixed charges, while the high particle concentration is taken into account by means of a cell model. The network simulation method used makes it possible to solve the problem without any restrictions on the values of the parameters such as particle concentration, membrane thickness, fixed charge density in the membrane, viscous drag in the membrane, number and valence of ionic species, electrolyte concentration, etc. The theoretical model used is similar to the one presented by Ohshima [H. Ohshima, J. Colloid Interface Sci. 225 (2000) 233], except for the use of the Shilov–Zharkikh, rather than the Levine–Neale, boundary condition for the electric potential, and the inclusion in the force balance equation of an additional term corresponding to the force exerted by the liquid on the core of the moving particle [J.J. López-García, C. Grosse, J. Horno, J. Colloid Interface Sci. 265 (2003) 327]. The obtained results only coincide with existing analytical expressions for low particle concentrations, low particle charge, and when the electrolyte concentration is high, the membrane is thick, and its resistance to the fluid flow is high. This suggests that most interpretations of the electrophoretic mobility of soft particles in concentrated suspensions require numerical calculations.Existing analytical expressions for the electrophoretic mobility u ˜ e are only in good agreement with numerical results for low particle concentration ϕ, low particle charge Q, and when the electrolyte concentration is high, the membrane is thick, and its resistance to the fluid flow is high.
Keywords: Electrophoretic mobility; Soft particle; Concentrated suspension; Network simulation method;

Because electroacoustic techniques are gaining interest in many fields of colloid science, a number of theories dealing with the phenomenon of electrophoresis in high-frequency (on the order of the MHz) electric fields have been developed. In the present work we propose a straightforward derivation of a simple formula for the dynamic mobility of colloidal particles in mildly concentrated systems. Starting with a simple expression for the electrophoretic mobility in dilute suspensions, given as a function of the zeta potential and of the dipole coefficient, we introduce successive corrections related to: (i) the back flow of fluid induced by the electrophoretic motion of the particles; (ii) the electrostatic interactions among particles; (iii) the difference between the macroscopic and the external electric fields; (iv) the difference between the zero-momentum and the laboratory reference frames. Considering furthermore that the frequency dependence of the dipole coefficient is due to the Maxwell–Wagner–O'Konski double-layer relaxation, we obtain a mobility expression that compares well with other (semi)analytical models and (in proper conditions) with numerical cell-model calculations. However, its main merit is that it allows to understand, to a large extent, the physical origin of the frequency and volume fraction dependences of the dynamic mobility.A simple model is derived to explain the frequency and volume fraction dependence of the dynamic electrophoretic mobility of concentrated suspensions. The evaluation compares favorably with existing more elaborate methods in a wide range of conditions.
Keywords: Dynamic mobility; Electroacoustic methods; Hydrodynamic interactions; Concentrated dispersions;

Alternative models for determining the surface energy components in offset printing by M. Järn; C.-M. Tåg; J. Järnström; B. Granqvist; J.B. Rosenholm (668-676).
Different ways of calculating surface energy components for substrates used in offset printing are compared. The results of the very useful van Oss–Chaudhury–Good bi–bidentate model (vOCG) are simplified to mono–bidentate and mono–monodentate models. The unbalance in the acid–base values often obtained by the vOCG model is strongly reduced when applying the simple mono–monodentate model. Moreover, the frequently encountered problem of negative square roots of the acid and base components is removed. An attempt to describe the ink transfer during offset printing by calculating theoretical works of adhesion between ink/plate and ink/paper is also made. The effect of paper roughness on the wetting was studied with atomic force microscopy (AFM).
Keywords: Offset printing; Surface energy; Acid–base; Contact angle; Adhesion; Roughness;

We describe here a numerical method for finding the local contact angles of a drop in the case of partial wetting for given values of the drop volume and capillary length when there are data available for the whole contact line of the drop. There are no special restrictions imposed on the type of the contact line: the solid substrate on which the drop rests can be heterogeneous or rough or both, it can be horizontal or tilted. The method is intended to be used in conjunction with experimental results similarly to the axisymmetric drop shape analysis-diameter (ADSA-D) and analysis-profile (ADSA-P) methods. The numerical method is essentially an iterative minimization procedure based on the local variations approach. It allows finding drop shapes which are not axially symmetric. The contact angles are then determined from the obtained shape of the drop. Several examples of applying the method are described for a drop on: flat, horizontal but heterogeneous substrate; flat, tilted substrate, and grooved horizontal substrate.A numerical method is described for finding the local contact angles of a nonaxisymmetric drop for given values of the drop volume and capillary length when there are data available for the whole contact line of the drop.
Keywords: Liquid drops; Nonaxisymmetric drop shape analysis; Local contact angles;

Impact of phase composition on water adsorption on inorganic hybrids “salt/silica” by Larisa G. Gordeeva; Ivan S. Glaznev; Elena V. Savchenko; Vladislav V. Malakhov; Yuri I. Aristov (685-691).
The effect of a “guest–host” interaction on the phase composition and sorption properties of the composite sorbents “salt in a porous host matrix” has been studied. The matrix was a mesoporous silica of KSK type, while the confined salts were CaCl2, CuSO4, MgSO4, and Na2SO4. Both structure and properties of the composites were studied by X-ray diffraction, titration in the pH range of 2–9, differential dissolution, and TG techniques. Chemical interaction between the silica surface and the salt during preparation results in the formation of the salt surface complexes and stabilization of the dispersed salt in two phases, namely, a crystalline phase and an X-ray amorphous phase. The water sorption properties of the composites depend on the phase composition and can be intently modified by using variation of the preparation conditions.
Keywords: Composites “salt/silica”; Mesoporous silica gel; Inorganic salts; Surface interaction; Metal cation adsorption; Water adsorption;

Interaction of quinapril anion with cationic surfactant micelles of cetyltrimethylammonium bromide by Olivera Čudina; Ivana Janković; Mirjana Čomor; Sote Vladimirov (692-696).
In this study, the interaction of the anion of quinapril (QUIN), angiotensin converting enzyme (ACE) inhibitor, with cationic surfactant cetyltrimethylammonium bromide (CTAB) was investigated. The effect of cationic micelles on the spectroscopic and acid–base properties of QUIN was studied at pH 8. The binding of QUIN anion to CTAB micelles implied a shift in drug acidity constant ( p K a water − p K a micelle = 1.39 ) proving the great affinity of negatively charged QUIN ion for the positively charged CTAB micelle surface. The strong dependence of the partition coefficient K x on QUIN concentration, obtained by using pseudo-phase model, is consistent with an adsorption-like phenomenon. From the dependence of differential absorbance at λ = 272   nm on CTAB concentration, by using mathematical model that treats the solubilization of QUIN anion as its binding to specific sites in the micelles (Langmuir adsorption isotherm), the binding constant K b = ( 2.3 ± 0.4 ) × 10 3   mol −1 dm 3 was obtained. QUIN–CTAB binding constant was also calculated from micellar liquid chromatography (MLC) and this method was found to be not accurate enough for its determination.Absorption spectra of quinapril anion change upon addition of increasing amounts of CTAB. The change is most pronounced at λ = 272   nm .
Keywords: Quinapril anion; CTAB; Micelles; Binding constant; Partition coefficient; MLC;

A microfluidic fluorous solid-phase extraction chip for purification of amino acids by Guoqing Hu; Jacky S.H. Lee; Dongqing Li (697-702).
An electrokinetically-driven microfluidic chip was developed to realize beads-based solid-phase extraction (SPE) of amino acids. This chip uses a two-level (deep/shallow) poly(dimethylsiloxane) (PDMS) microchannel network to confine the fluorous reversed-phase silica beads within the SPE chamber. The mixture of fluorous tagged and non-tagged amino acids was carried into the fluorous solid-phase extraction (F-SPE) chamber by electrokinetic pumping and was successfully separated and extracted. By adding a reference material to the sample, the extraction efficiency of the eluted fluorous-tagged amino acid was calculated using the detection results from mass spectrometry (MS). The F-SPE microchips showed good reproducibility and efficiency, yielding an average extraction efficiency of 55% with a RSD of 10.6% under the typical experimental conditions.A simple but effective fabrication procedure was developed to build a retaining chamber for silica beads in the poly(dimethylsiloxane) (PDMS) microchannel. The resulting structure was a combination of two layers of PDMS slabs that contained two sets of channels with different depths.
Keywords: Microfluidics; Fluorous solid-phase extraction; Microbeads; PDMS;

Control of droplet size and spacing in micrometer-sized polymeric dewetting patterns by Olaf Karthaus; Suguru Mikami; Yuichi Hashimoto (703-705).
When a polymer solution is cast on a flat substrate and the solvent is allowed to evaporate, dewetting might take place. Instead of a continuous film, the polymer forms micrometer-sized droplets. By controlling the solvent casting process with the help of a roller apparatus, the size and spacing of the polymer droplets can be adjusted. We investigated the effect of polymer concentration and roller speed on the pattern dimensions and found that higher concentrations lead to larger polymer droplets (from 1 to 11 μm), whereas faster roller speeds lead to a wider interdroplet spacing (from 4 to 130 μm).
Keywords: Polystyrene; Dewetting; Mica; Droplet arrays; 2D ordering;