Journal of Colloid And Interface Science (v.293, #1)



Particle deposition onto micropatterned charge heterogeneous substrates: Trajectory analysis by Neda Nazemifard; Jacob H. Masliyah; Subir Bhattacharjee (1-15).
A trajectory analysis of particles near a micropatterned charged substrate under radial impinging jet flow conditions is presented to investigate the effect of surface charge heterogeneity on particle trajectory and deposition efficiency. The surface charge heterogeneity is modeled as concentric bands of specified width and pitch having positive and negative surface potentials. The flow distribution is obtained using finite element analysis of the governing Navier–Stokes equations. The particle trajectory analysis takes into consideration the hydrodynamic interactions, gravity, van der Waals and electrostatic double layer interactions. The presence of surface charge heterogeneity on the substrate gives rise to an oscillating particle trajectory near the collector surface due to repulsive and attractive forces. As a result of the coupled effects of hydrodynamic and colloidal forces, the particle trajectories and deposition efficiencies are increasingly affected by surface charge heterogeneity as one moves radially away from the stagnation point. The results indicate that it is possible to render collectors with up to 50% favorable surface fraction completely unfavorable by modifying the ratio of the radial to normal fluid velocity. Utilizing the real favorable area fraction of the collector, the patch model expression for calculating the deposition efficiency is modified for impinging jet flow geometry.Trajectory analysis of colloidal particles on micropatterned charge heterogeneous substrates in an impinging jet flow system is presented.
Keywords: Particle deposition; Impinging jet flow; Trajectory analysis; Charge heterogeneity; Micropatterned surface; Patch model;

Two waste materials—bottom ash, a power plant waste, and de-oiled soya, an agricultural waste—are meticulously and successfully used as adsorbent for the removal and recovery of a hazardous triphenylmethane dye, Brilliant Blue FCF. Both the materials were characterized by chemical analysis, IR, DTA, SEM and XRD studies. Their physical characteristics like surface area, porosity, density and loss on ignition were also determined. The adsorption of the dye over both materials was achieved under different pH, adsorbate concentration, sieve size, adsorbent dosage, contact time and temperature, etc. conditions. For both the systems Langmuir and Freundlich adsorption isotherm models were applied and, based on these models, useful thermodynamic parameters were calculated. For both the adsorbents, the kinetic measurements indicate that the adsorption process follows first order kinetics and film diffusion and particle diffusion mechanisms are operative at lower and higher concentrations, respectively, in each case. By percolating the dye solution through fixed-bed columns the bulk removal of the Brilliant Blue FCF was carried out and necessary parameters were determined to find out the percentage saturation of both the columns. Recovery of Brilliant Blue FCF was made by eluting dilute NaOH of pH 11 through each column.
Keywords: Brilliant Blue FCF; Bottom ash; De-oiled soya; Adsorption; Kinetics;

Sorption of Sr(II) and Eu(III) onto pyrite under different redox potential conditions by Aude Naveau; Fanny Monteil-Rivera; Jacques Dumonceau; Hubert Catalette; Eric Simoni (27-35).
Understanding sorption processes is fundamental for the prediction of radionuclide migration in the surroundings of a deep geological disposal of high-level nuclear wastes. Pyrite (FeS2) is a mineral phase often present as inclusions in temperate soils. Moreover, it constitutes an indirect corrosion product of steel, a containment material that is candidate to confine radionuclides in deep geological disposals. The present study was thus initiated to determine the capacity of pyrite to immobilize Sr(II) and Eu(III). An air oxidized pyrite and a freshly acid-washed (non-oxidized) pyrite were used in background electrolytes of varying reducing–oxidizing ability (NaCl, NH3OHCl, and NaClO4) to study the sorption of both cationic species. The sorptive capacity of pyrite appeared directly correlated to the oxidation of the surface. Non-oxidized pyrite had nearly no affinity for the studied cations whereas Sr(II) and Eu(III) species were significantly retained by oxidized pyrite surface. Using the surface complexation theory, sorption mechanisms were modeled with the Fiteql v3.2 and the Jchess 2.0 codes. Sorption of both Sr and Eu was well fitted, assuming hydroxylated species as the major surface species. This study demonstrates that not only the components of a barrier but also the redox conditions and speciations should be well characterized to predict transport of contaminants in the surrounding of a nuclear wastes disposal.
Keywords: Reducing conditions; Pyrite; Sorption; Sr(II); Eu(III); Surface complexation;

Removal of boron from aqueous solution by clays and modified clays by Senem Karahan; Mürüvvet Yurdakoç; Yoldaş Seki; Kadir Yurdakoç (36-42).
In order to increase the adsorption capacities of bentonite, sepiolite, and illite for the removal of boron form aqueous solution, the clay samples were modified by nonylammonium chloride. Specific surface areas of the samples were determined as a result of N2 adsorption–desorption at 77 K using the BET method. X-ray powder diffraction analysis of the clays and modified clays was used to determine the effects of modifying agents on the layer structure of the clays. The surface characterization of clays and modified clay samples was conducted using the FTIR technique before and after the boron adsorption. For the optimization of the adsorption of boron on clays and modified clays, the effect of pH and ionic strength was examined. The results indicate that adsorption of boron can be achieved by regulating pH values in the range of 8–10 and high ionic strength. In order to find the adsorption characteristics, Langmuir, Freundlich, and Dubinin–Radushkevich adsorption isotherms were applied to the adsorption data. The data were well described by Freundlich and Dubinin–Radushkevich adsorption isotherms while the fit of Langmuir equation to adsorption data was poor. It was reached that modification of bentonite and illite with nonylammonium chloride increased the adsorption capacity for boron sorption from aqueous solution.
Keywords: Boron; Adsorption; Clay; Modified clay; FTIR;

The effect of active carbon on the reduction of concentrated nitric acid by HCOOH by Akane Miyazaki; Kazumasa Shibazaki; Ioan Balint (43-51).
In nuclear industry, removal of nitric acid from solutions is required in the course of chemical separation and waste treatment procedure as well as in chemical conversion steps. The reduction of HNO3 by HCOOH to gaseous products such as nitrogen, nitrogen oxides, and carbon dioxide is an attractive way to accomplish the denitration. A typical problem for the denitration is the existence of the induction period. The induction period has been explained as the time necessary to increase the concentration of HNO2, which is an important reaction intermediate, above a threshold value. In this study, adsorption sites on the surface of active carbon were found to promote HNO2 formation and efficiently suppress the induction period. Induction time was shortened by increasing the amount of active carbon in the solution. When the solution contains 3 M HNO3 and 1 M HCOOH, 10 g/L of active carbon was enough to eliminate the induction period at 50 °C. The catalytic effect exhibited by active carbon was similar to that reported for Pt/SiO2. Therefore, on the surface of active carbon, there is a redox cycle, where HNO3 is reduced to HNO2 and then the oxidized surface site will be reduced by HCOOH.The surface of active carbon was found to promote HNO2 formation and efficiently suppresses the induction period of denitration reaction. The time course of HNO2 formation as a function of AC amount suspended in the reacting solution.
Keywords: Chemical denitration; Active carbon; Nitric acid; Formic acid;

Cooperative α-helix formation of β-lactoglobulin induced by sodium n-alkyl sulfates by J. Chamani; A.A. Moosavi-Movahedi; O. Rajabi; M. Gharanfoli; M. Momen-Heravi; G.H. Hakimelahi; A. Neamati-Baghsiah; A.R. Varasteh (52-60).
It is generally assumed that folding intermediates contain partially formed native-like secondary structures. However, if we consider the fact that the conformational stability of the intermediate state is simpler than that of the native state, it would be expected that the secondary structures in a folding intermediate would not necessarily be similar to those of the native state. β-Lactoglobulin is a predominantly β-sheet protein, although it has a markedly high intrinsic preference for α-helical structure. The formation of non-native α-helical intermediate of β-lactoglobulin was induced by n-alkyl sulfates including sodium octyl sulfate, SOS; sodium decyl sulfate, SDeS; sodium dodecyl sulfate, SDS; and sodium tetradecyl sulfate, STS at special condition. The effect of n-alkyl sulfates on the structure of native β-lactoglobulin at pH 2 was utilized to investigate the contribution of hydrophobic interactions to the stability of non-native α-helical intermediate. The addition of various concentrations of n-alkyl sulfates to the native state of β-lactoglobulin (pH 2) appears to support the stabilized form of non-native α-helical intermediate at pH 2. The m values of the intermediate state of β-lactoglobulin by SOS, SDeS, SDS and STS showed substantial variation. The enhancement of m values as the stability criterion of non-native α-helical intermediate state corresponded with increasing chain length of the cited n-alkyl sulfates. The present results suggest that the folding reaction of β-lactoglobulin follows a non-hierarchical mechanism and hydrophobic interactions play important roles in stabilizing the non-native α-helical intermediate state.
Keywords: β-Lactoglobulin; α-Helix; Non-native α-helical intermediate; n-Alkyl sulfate; Protein folding; Non-hierarchical mechanism; Thermodynamics; Circular dichroism; Binding isotherm;

The interaction between the fluorocarbon surfactant, sodium perfluorooctanoate (SPFO), and β-lactoglobulin (BLG) was studied. In particular, the effects of cationic surfactants, such as alkyltriethylammonium bromide ( C n NE , n = 8 , 10, 12), on SPFO–BLG interaction were examined. It was shown that the anionic fluorocarbon surfactant, SPFO, was a strong denaturant of BLG. The ability of SPFO to denature BLG could be weakened by the addition of C n NE . The effect of C n NE on SPFO–BLG interaction was related to the hydrocarbon chain length of C n NE , and also the molar ratio of the added C n NE to the SPFO in SPFO–BLG solutions ([ C n NE ]/[SPFO]). Our findings might provide a way to design surfactant systems that are less denaturing to proteins or tailor the ability of surfactant to denature proteins through the appropriate mixing with other surfactants.The ability of sodium perfluorooctanoate to denature β-lactoglobulin could be weakened by cationic surfactants. The weakening effect was related to the cationic surfactant hydrocarbon chain length and concentration.
Keywords: β-Lactoglobulin; Sodium perfluorooctanoate; Alkyltriethylammonium bromide; Circular dichroism; Fluorescence;

A small section of nonspherical particles can be observed in the further growth of spherical gold colloids exposed to a mixture of NH2OH and HAuCl4. The concentration ratio of [NH2OH]:[HAuCl4] is critical for the formation of nonspherical particles as higher ratios produce lower yields and smaller of such particles. These concentrations also affect the reaction kinetics; the reaction rate increases with [NH2OH], while independent of [HAuCl4], which we believe is due to the specific adsorption of AuCl 4 onto gold surface. These nonspherical particles come from the preferential growth of {111} facets as indicated by their TEM images and electron diffraction patterns. We propose this preferential growth is ascribed to the preferential adsorption of AuCl 4 on {111} facets, and some competition which determines the yield of nonspherical particles exists between the AuCl 4 adsorption and the AuCl 4 reduction, faster reduction counteracting the effect of this preferential adsorption and thus suppressing nonspherical particle. This result probably provides some guidance to develop a shape-controlled synthesis of gold particles without any additives.The competition between the adsorption of AuCl 4 − and the reduction of AuCl 4 − at the surface of seed particles determine the shape distribution of resulting gold colloids.
Keywords: Gold nanoparticles; Seeding growth; Preferential adsorption; Shape-controlled; Kinetics; Nonspherical; AuCl 4;

Influences of the magnetic interaction between particles and the aspect ratio of particles on aggregate structures in a colloidal dispersion composed of rod-like ferromagnetic particles were investigated by means of the cluster-moving Monte Carlo method. The internal structures of the aggregates obtained in simulations were analyzed in terms of the number density distribution of the clusters and radial distribution functions. The results show that as the magnetic interaction between particles increases, many small clusters such as anti-parallel particle pairs, raft-like clusters, and small loop-like clusters are formed; these gather to form larger aggregates. In the case of a relatively strong magnetic interaction between particles, solid-like rectangular clusters are formed when the aspect ratio is approximately 2, since the suitable distance between magnetic charges enables particles to form a fundamental structure of two normal anti-parallel particle pairs. As the aspect ratio increases beyond 2, many more stable raft-like clusters are formed, since the increase in distance between magnetic charges makes the two normal anti-parallel particle pair structures unstable. For a significantly larger aspect ratio, large network microstructures are produced by the formation of many chain-like and loop-like structures.
Keywords: Rod-like particle; Aspect ratio; Ferromagnetic colloidal dispersion; Aggregate structure; Monte Carlo simulation;

Nanoscaled spherical silica particles were directly coated with the titania nanoparticles by means of a heterogenic coagulation. Silica was prepared by the Stöber method, titania by a hydrolysis–condensation reaction of tetrapropylorthotitanate under acidic conditions. The on-line tracking of the coating process was performed by measuring the change in zeta potential during the gradual addition of a titania sol to the spherical silica particles. Silica particles of various sizes were used to determine the consumption of the titania sol in the dependence upon the particle size. The coated and uncoated particles were characterized by zeta-potential measurements, acoustic attenuation spectroscopy, dynamic light scattering, and scanning electron microscopy.
Keywords: Titania; Silica; Stöber method; Nanoparticles; Sol; Coating; Heterogenic coagulation; Zeta-potential;

In this study the temperature-induced gelation of butadiene–acrylonitrile latex containing the added temperature-responsive polymer surfactant, poly(NIPAM-co-PEGMa) is investigated for the first time. (NIPAM and PEGMa are N-isopropylacrylamide and poly(ethylene glycol)methacrylate, respectively.) The results are compared with temperature-induced gelation of oil-in-water emulsions containing 1-bromohexadecane. The effect of added anionic surfactant, NaDBS (sodium dodecylbenzene sulfonate) on the temperature-induced gelation process and mechanism is considered. It was found that the gelation temperature ( T gel ) for the latex occurs at the cloud point temperature ( T cpt ) of the polymer and that T gel is much less affected by added NaDBS than is the case for emulsion gelation. The mathematical predictive theory recently derived for temperature-induced emulsion gelation was applied to the latex data and gave a good fit (i.e., T gel ∼ 1 / C p , where C p is the concentration of added poly(NIPAM-co-PEGMa)). However, the causes for the variation of T gel with C p for temperature-induced latex and emulsion gelation are different. The variation of T gel for latex gelation in the presence of added NaDBS originates from surfactant association with poly(NIPAM-co-PEGMa) which increased T cpt . In the case of emulsion gelation there are electrostatic interactions above T cpt which control T gel . The subtle difference in the temperature-induced latex gelation mechanism is a consequence of the very high latex surface area (cf. emulsion), small inter-particle separation and the presence of electrolyte. The reason that T gel follows 1 / C p for the latex is due to a fortuitous T cpt ∼ 1 / C p relationship that applies for poly(NIPAM-co-PEGMa) solution in the presence of NaDBS. The work presented here shows that addition of poly(NIPAM-co-PEGMa) to dispersions gives a versatile method for temperature-triggered gelation. Furthermore, the theory presented provides a framework for predicting their gelation temperatures.
Keywords: Intelligent polymers; N-isopropylacrylamide; Poly(ethylene glycol)methacrylate; Temperature-induced gelation;

Polyethylenimine-modified montmorillonite (N-MMT) was used to prepare gold nanoparticles, where the montmorillonite (MMT) acted as a solid support to retain the conformation of polyethylenimine (PEI), and the amino groups of PEI were used simultaneously to both complex and reduce the gold ions. From the results of X-ray diffraction, it is apparent that the reduction of gold ions occurs primarily on the MMT surface. In the presence of MMT, the formation of a flattened configuration on the clay instead of stretched-out ethylenimine segments of PEI results in the formation of smaller gold particles. With a higher acidification ratio, the recharging of the MMT surface with positive ammonium ionic sites of PEI is likely to prevent the flocculation of clay and thus facilitate the reduction of gold. The rate of gold reduction with N-MMT is faster at low pH values, this being in contrast to the usual trend observed for the reduction of gold ions. The use of PEI adsorbed onto MMT has been shown to be able to act simultaneously as both a protective template and as a reducing agent, thereby greatly simplifying the process for preparing gold nanoparticles.
Keywords: Metal nanoparticles; Montmorillonite;

Effects of amino acids on the formation of hematite particles in a forced hydrolysis reaction by Kazuhiko Kandori; Masaji Sakai; Shoko Inoue; Tatsuo Ishikawa (108-115).
The influence of amino acids on the formation of hematite particles from a forced hydrolysis reaction of acidic FeCl3 solution was examined. The spherical particles were produced on the systems with L-phenylalanine (L-Phe), L-serine (L-Ser) and L-alanine (L-Ala), though L-glutamine (L-Gln) and L-glutamic acid (L-Glu) gave ellipsoidal hematite particles. This morphological change in hematite particles is consistent with the order of stability constant of amino acids against to Fe3+ ions (K). The hematite particles produced with L-Glu, L-Gln and L-Ser were highly porous because they are formed by aggregation of cluster particles. These particles exhibited microporous behavior by outgassing the particles below 200 °C while they changed to mesoporous after treating above 300 °C by elimination of amino acids molecules remained between the cluster particles within the hematite particles. The hematite particles strongly depended on the nature of amino acids such as alternation of solution pH and adsorption affinity to β-FeOOH and/or polynuclear primary (PN) particles. The systems on L-Ala and L-Phe, showing very rapid phase transformation from β-FeOOH to hematite, exhibited the Ostwald ripening. A rotational particle preparation procedure suggested that the morphology of hematite particle is governed by the mode and strength of amino acid adsorption onto β-FeOOH and/or PN particles.The extent of morphological and inner structural changes in hematite particles are consistent with the order of stability constant of amino acid complexes with Fe3+ ions.
Keywords: Hematite; Effects of amino acids; Amino acids; Forced hydrolysis reaction; Ellipsoidal particle; Aggregate; Micropores; Mesopores;

Orthokinetic flocculation of clay dispersions at pH 7.5 and 22 °C has been investigated to determine the influence of interfacial chemistry and shear on dewatering and particle interactions behavior. Modification of pulp chemistry and behavior was achieved by using kaolinite and Na-exchanged (swelling) smectite clay minerals, divalent metal ions (Ca(II), Mn(II)) as coagulants and anionic polyacrylamide copolymer (PAM A) and non-ionic polyacrylamide homopolymer (PAM N) as flocculants. The pivotal role of shear, provided by a two-blade paddle impeller, was probed as a function of agitation rate (100–500 rpm) and time ( 15 / 60 s). Particle zeta potential and adsorption isotherms were measured to quantify the interfacial chemistry, whilst rheology and cryogenic SEM were used to investigate particle interactions and floc structure and aggregate network, respectively. Osmotic swelling, accompanied by the formation of “honeycomb” particle network structure and high yield stress, was produced by the Na-exchanged smectite, but not kaolinite, dispersions. Dispersion of the clay particles in 0.05 M Ca(II) or Mn(II) solution led to a marked reduction in particle zeta potential, complete suppression of swelling, honeycomb network structure collapse and a concomitant reduction in shear yield stress of smectite pulps. Optimum conditions for improved, orthokinetic flocculation performance of negatively charged clay particles, reflecting faster settling flocs comprised (i) coagulation, (ii) moderate agitation rate, (iii) shorter agitation time, and (iv) anionic rather than non-ionic PAM. The optimum dewatering rates were significantly higher than those produced by standard, manual-mixing flocculation techniques (plunging and cylinder inversion) commonly used in industry for flocculant trials. The optimum flocculation conditions did not, however, have a significant impact on the final sediment solid content of 20–22 wt%. Further application of shear to pre-sedimented pulps improved consolidation by 5–7 wt% solid. Higher shear yield stresses and greater settling rates were displayed by PAM A based than PAM N based pulps and this is attributed to the former's more expanded interfacial conformation and greater clay particles bridging ability. It appears that the intrinsic clay particles' physico-chemical properties and interactions limit compact pulp consolidation.
Keywords: Smectite; Kaolinite; Clay mineral flocculation; Polyacrylamide; Settling behavior; Sedimentation; Dewatering; Pulp consolidation;

Adsorption of simple aromatic compounds on activated carbons by Francisco Villacañas; Manuel Fernando R. Pereira; José J.M. Órfão; José L. Figueiredo (128-136).
The adsorption of model aromatic compounds (phenol, aniline, nitrobenzene) on modified activated carbons has been investigated. Electrostatic and dispersive adsorbate/adsorbent interactions are involved in this process. Their influence on the uptake of the above mentioned aromatic compounds has been evaluated using different solution pH conditions and activated carbon samples with different surface chemistries. These samples were obtained by modification of a commercial activated carbon by means of chemical treatment with HNO3 (acid sample) and thermal treatment under a flow of H2 (basic sample). The textural properties were not significantly changed after these modifications. The best uptake for all the adsorptives under most of the pH conditions used corresponded to the basic sample, which means that dispersive interactions are the most important in this process. However, electrostatic interactions cannot be neglected, as can be seen from the uptakes for the same sample at different pH. In the case of aniline at pH 2, electrostatic interactions are predominant, and the best uptake corresponds to the acid sample. The influence of textural properties on the adsorption process was also investigated, by comparing with another commercial activated carbon. As expected, for this type of organic compounds the uptake increases with the micropore surface area.Activated carbon surface chemistry and solution pH play a key role on the adsorption of monosubstituted aromatic compounds.
Keywords: Activated carbon; Surface chemistry; Phenol; Aniline; Nitrobenzene; Adsorption;

Mixed convection flow, heat, and mass transfer about an isothermal vertical flat plate embedded in a fluid-saturated porous medium and the effects of viscous dissipation and thermophoresis in both aiding and opposing flows are analyzed. The similarity solution is used to transform the problem under consideration into a boundary value problem of coupled ordinary differential equations, which are solved numerically by using the shooting method. Numerical computations are carried out for the nondimensional physical parameter. The results are analyzed for the effect of different physical parameters such as thermophoretic, mixed convection, inertia parameter, buoyancy ratio, and Schmid number on the flow, heat, and mass transfer characteristics. Two cases are considered, one corresponding to the presence of viscous dissipation and the other to the absence of it.
Keywords: Heat and mass transfer; Viscous dissipation; Porous media; Mixed convection; Thermophoresis;

Preparation of ion-exchange fiber fabrics by electrospray deposition by Hidetoshi Matsumoto; Yuji Wakamatsu; Mie Minagawa; Akihiko Tanioka (143-150).
Ion-exchange fiber (IEF) fabrics were prepared by electrospray deposition (ESD) and post-deposition chemical modification of their surfaces. Nonwoven fibrous fabrics were obtained from the solutions of synthetic polymers—polystyrene (PS) and poly(4-vinylpyridine) (P4VP)—of various concentrations. The diameter of the fiber in the fabrics ranged from 600 nm to 1.70 μm. Cation- and anion-exchange fiber (CEF and AEF) fabrics were obtained from the sulfonation of PS fabrics and the quaternization of P4VP fabrics, respectively. These fabrics were thoroughly characterized by a series of techniques, such as scanning electron microscopy (SEM), permporometry, nitrogen adsorption measurements, and potentiometric titrations. The SEM images showed that the fabrics had a porous structure after their chemical modification. The mean pore size, porosity, and specific surface area of the flow-through pores were 1.67–3.53 μm, about 80%, and 13 m2/g, respectively. The ion-exchange capacity was in the range from 0.78 to 1.34 mmol/g. The AEF fabric, on the other hand, showed a high specific surface area, i.e., the Brunauer–Emmett–Teller (BET) surface area of 600 m2/g, due to the formation of much smaller pores on the surface of the fiber structure in the fabric. The secondary chemical modification of the nano-microfiber fabrics by ESD provides novel functional materials with a large adsorption capacity and a high catalytic activity.Ion-exchange fiber fabrics were prepared by electrospray deposition from the solutions of synthetic polymers, polystyrene (PS) and poly(4-vinylpyridine) (P4VP), and post-deposition chemical modification of their surfaces.
Keywords: Electrospray deposition; Ion exchange; Nanofiber fabric; Polystyrene; Poly(4-vinylpyridine);

Filling kinetics of liquids in nanochannels as narrow as 27 nm by capillary force by Anpan Han; Giampietro Mondin; Nicole G. Hegelbach; Nicolaas F. de Rooij; Urs Staufer (151-157).
We report the filling kinetics of different liquids in nanofabricated capillaries with rectangular cross-section by capillary force. Three sets of channels with different geometry were employed for the experiments. The smallest dimension of the channel cross-section was respectively 27, 50, and 73 nm. Ethanol, isopropanol, water and binary mixtures of ethanol and water spontaneously filled nanochannels with inner walls exposing silanol groups. For all the liquids the position of the moving liquid meniscus was observed to be proportional to the square root of time, which is in accordance with the classical Washburn kinetics. The velocity of the meniscus decreased both with the dimension of the channel and the ratio between the surface tension and the viscosity. In the case of water, air-bubbles were spontaneously trapped as channels were filled. For a binary mixture of 40% ethanol and water, no trapping of air was observed anymore. The filling rate was higher than expected, which also corresponds to the dynamic contact angle for the mixture being lower than that of pure ethanol. Nanochannels and porous materials share many physicochemical properties, e.g., the comparable pores size and extremely high surface to volume ratio. These similarities suggest that our nanochannels could be used as an idealized model to study mass transport mechanisms in systems where surface phenomena dominate.
Keywords: Ethanol; Isopropanol; Water; Ethanol–water mixture; Capillary force; Wetting; Filling kinetics; Nanochannels; Porous materials;

Thermocapillary flow in double-layer fluid structures: An effective single-layer model by Nivedita R. Gupta; Hossein Haj-Hariri; Ali Borhan (158-171).
Thermocapillary flows are of considerable technological importance in materials processing applications such as crystal growth from the melt, particularly under microgravity conditions where the influence of buoyancy-driven convection is minimized. In this study, thermally driven convection within a differentially heated rectangular cavity containing two immiscible liquid layers is considered in the absence of gravity. The introduction of a more viscous encapsulant layer leads to a significant reduction in the intensity of the thermocapillary flow within the encapsulated layer. Interface deformations are small when the contact line of the interface is pinned on the solid boundaries. The higher viscosity of the encapsulant layer gives rise to a larger pressure gradient in that layer, thereby resulting in interface deformations that are qualitatively different from those observed at the free surface in the absence of the encapsulant layer. The flow pattern in the encapsulated layer and the resulting interface deformations are strongly dependent on both the thickness and the viscosity of the encapsulant layer. It is shown that the flow within the encapsulated layer may be closely approximated by simply considering the single-layer problem with a modified stress condition at the interface. The modified tangential stress balance for the effective single-layer model is derived based on asymptotic results for small-aspect-ratio double-layer systems and the insight gained from double-layer computations for finite-aspect-ratio systems. It is shown that the single-layer model accurately predicts the flow in the double-layer system even for large aspect-ratios.
Keywords: Thermocapillary flow; Marangoni stress; Interface deformation;

The wettability of polytetrafluoroethylene and polymethyl methacrylate by aqueous solution of two cationic surfactants mixture by Katarzyna Szymczyk; Anna Zdziennicka; Bronisław Jańczuk; Wiesław Wójcik (172-180).
Advancing contact angle (θ) measurements were carried out for aqueous solutions of cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPyB) mixtures on polytetrafluoroethylene (PTFE) and polymethyl methacrylate (PMMA). The obtained results indicate that the wettability of PTFE and PMMA by aqueous solutions of CTAB and CPyB mixtures depends on the composition and concentration of the mixture; however, synergism in the wettability does not exist. In the range of low concentrations of aqueous solution mixtures there is a linear dependence between the contact angle and composition of the mixtures, but at a concentration close to CMC a deviation from linear dependence is observed. In contrast to Zisman, there is no linear dependence between cos θ and the surface tension of aqueous solution of CTAB and CPyB mixtures, but a linear dependence exists between the adhesional and surface tension, and these lines have a slope −1 and −0.34 for PTFE and PMMA, respectively, which suggests that adsorption of CTAB and CPyB mixtures at water–air and PTFE–water is the same, and the orientation of the CTAB and CPyB molecules at both interfaces in the saturated monolayer should also be the same. Adsorption of these mixtures at water–air interface is considerably higher than at PMMA–water interface, and CTAB and CPyB molecules should be parallelly oriented to PMMA surface in the saturated monolayer. Extrapolation of the straight lines to the points corresponding to the surface tension of aqueous solution, which completely spreads over the PTFE and PMMA surface, gives a critical surface tension of wetting equal to 23.44 and 33.13 mN/m, respectively. The value of 23.44 mN/m is higher than that of the surface tension of PTFE, but the value of 33.13 is lower than that of Lifshitz–van der Waals components of PMMA surface tension. On the basis of the critical surface tension, the surface tension of PTFE and PMMA, the Young equation, and thermodynamic analysis of the adhesion work of aqueous solution of surfactant to polymer surface, it was found that for PTFE and PMMA the changes of the contact angle of aqueous solution of two cationic surfactants mixtures on their surfaces as a function of the solution concentration resulted only from the decrease of the polar component of the solution surface tension.
Keywords: Wettability; Contact angle; Cationic surfactant; Polytetrafluoroethylene; Polymethyl methacrylate;

The spontaneous curvature ( H 0 ), mean and Gaussian bending constants ( k c and k ¯ c ), as defined in the well-known Helfrich expression, have been calculated from a detailed model for a thermodynamically open surfactant layer. The effect of head group cross-section area, surfactant tail length and electrolyte concentration for monovalent ionic surfactants have been investigated. Geometrical packing constraints subjected to the aggregated hydrocarbon tails and electrostatics are found to be the dominant contributions to H 0 , k c and k ¯ c . In addition, the transition from spherocylindrical micelles to vesicles were investigated in terms of the three parameters and the following simple expressions were derived as criteria for coexistence between micelles and vesicles H 0 = 1 / 4 ξ and 〈 N 〉 ves / 〈 N 〉 mic = exp [ 4 π ( k c + k ¯ c ) / k T ] , where ξ is the thickness of the hydrocarbon part of the film and 〈 N 〉 mic and 〈 N 〉 ves the average aggregation numbers of micelles and vesicles, respectively. However, it is found that the ratio 〈 N 〉 ves / 〈 N 〉 mic is order of magnitudes too large for vesicles to form at all in charged single-surfactant systems where the surfactant head is of moderate size.The coexistence between micelles and vesicles has been investigated in terms of the spontaneous curvature ( H 0 ) , mean and Gaussian bending constants ( k c and k ¯ c ).

Surface properties of systems that are mixtures of ionic surfactants and sugar derivatives—anionic surfactant sodium dodecyl sulfate and n-dodecyl-β-D-maltoside (SDS/DM) and cationic surfactant dodecyltrimethylammonium bromide and n-dodecyl-β-D-glucoside (DTABr/DG)—were investigated. The experimental results obtained from measurements of surface tension of mixtures with various ratio of ionic to nonionic components were analyzed by two independent theories. First is Motomura theory, derived from the Gibbs–Duhem equation, allowing for indirect evaluation of the composition of mixed monolayers and the Gibbs energies of adsorption, corresponding to mutual interaction between surfactants in mixed adsorbed film. As second theory we used our newly developed theoretical model of adsorption of ionic–nonionic surfactant mixtures. Using this approach, we were able to describe the experimental surface tension isotherms for mixtures of surface-active sugar derivatives and ionic surfactants. We obtained a good agreement with experimental data using the same set of model parameters for a whole range of studied compositions of a given surfactant mixture. The values of surface excess calculated from both theories agreed with each other with a reasonable accuracy. However, the newly developed model of adsorption of ionic–nonionic surfactant mixtures has the advantage of straightforward determination of surface layer composition. By the solution of equations of adsorption, one can obtain directly the values of surface excess of all components (surfactant ions, counterions, and nonionic surfactants molecules), which are present in the investigated system.
Keywords: Adsorption; Surface tension; Nonionic sugar surfactant; Ionic surfactant; Surfactant mixtures;

This work examines three related, but previously unexplored, aspects of membrane biophysics and colloid science in the context of atherosclerosis. First, we show that sphingomyelinase (SMase)-induced aggregation of low density lipoproteins (LDLs), coupled with LDL exposure to cholesterol esterase (CEase), results in nucleation of cholesterol crystals, long considered the hallmark of atherosclerosis. In particular, this study reveals that the order of enzyme addition does not effect the propensity of LDL to nucleate cholesterol crystals, raising the possibility that nucleation can proceed from either the intra- or extracellular space. Second, we demonstrate that ceramide-rich aggregates of LDL release cholesterol to neighboring vesicles far more rapidly, and to a greater extent, than does native LDL. A likely explanation for this observation is displacement of cholesterol from SM–Chol rafts by “raft-loving” ceramide. Third, we demonstrate that a time-independent Förster resonance energy transfer (FRET) assay, based on dehydroergosterol and dansylated lecithin and used previously to study cholesterol nanodomains, can be used to measure raft sizes (on the order of 10 nm) in model membrane systems. Taken together, these observations point to the possibility of an extracellular nucleation mechanism and underscore the important role that biological colloids play in human disease.Three aspects of membrane biophysics and colloid science in the context of atherosclerosis are explored: cholesterol nucleation from LDL, cholesterol transfer from LDL to receptor vesicles, and cholesterol–sphingomyelin raft sizes.
Keywords: Sphingomyelinase; LDL; Aggregation; Sphingomyelin; Cholesterol; Rafts;

In the present paper, we analyze the dependence of the second critical micelle concentration (second cmc) of ionic amphiphiles on the number of atoms in the hydrocarbon molecular chain, n c . A molecular thermodynamic model for the interaction energy between the end caps of rodlike micelles, g ( N ) , is introduced and the linear dependence of this object on n c analyzed, thus leading to a Stauff-Klevens-like behavior of the second cmc. The predictions agree with previously reported data for n-alkyldimethylbenzylammonium chloride (C n BACl) for n-alkylpyridinium chloride (C n PyCl) and n-alkyltrymethylammonium bromide (C n TABr) at 35 °C. These conclusions are reinforced by the conductivity, density, and ultrasound velocity measurements of the second cmc of several C n PyCl ( n = 12 , 14, 16) and n-alkylpyridinium bromides (C n PyBr, n = 12 , 14, 15, 16) presented in this paper.A molecular thermodynamic model of micellar growth has been formulated and a Stauff-Klevens-like relation derived for the second cmc.
Keywords: Ionic amphiphile self-assembly; Micellar growth; Second critical micelle concentration; Molecular thermodynamics; Stauff-Klevens-like behavior;

A note on the coating of an inclined plane in the presence of soluble surfactant by B.D. Edmonstone; O.K. Matar; R.V. Craster (222-229).
We consider the flow of a thin liquid film coating an inclined plane in the presence of a soluble surfactant. A two-dimensional three-equation model is derived using lubrication theory in the rapid diffusion limit and then used to investigate the stability of the fluid height and the surfactant surface and bulk concentrations. We present solutions for an insoluble surfactant system, which are then contrasted with those obtained for a system containing a soluble surfactant; both transient growth and fully nonlinear two-dimensional simulation results are discussed. Our results indicate that the characteristics of the fingering phenomena which accompany the flow are altered by the effects of solubility. In particular, we find that these effects destabilise the system further over an intermediate range of surfactant solubility.Fingering instability in surfactant-laden thin films flowing down an inclined plane. Panels (a), (d) and (g): film thickness; (b), (e) and (h): interfacial concentration; (c), (f) and (i): bulk concentration.

A new definition of the concentration-dependent “shielding factor” has been proposed, along with its particular value at a concentration assumed to be equal to critical micelle concentration (cmc). It has been shown that herein defined shielding factor enables one to calculate the values of monomer ( a x ) and counterion activities ( a y ) which are in better agreement with the measured ones than those calculated using Burchfield and Wooley's constant value of the shielding factor. In addition, it was shown that by using particular value of shielding factor at cmc, one is able to calculate the micellar charge radius which is dependent on aggregation number, counterion parameter and cmc, all of them having important implications for thermodynamic treatment of the micellization process.
Keywords: Activity; Ionic strength; Micelles; Potentiometry; Shielding factor;

Assembly of a model hydrophobic drug into cationic bilayer fragments by Débora B. Vieira; Luis F. Pacheco; Ana M. Carmona-Ribeiro (240-247).
Our previous work has shown that dioctadecyldimethylammonium bromide (DODAB) bilayer fragments (BF) presented antimicrobial activity, solubilized fungicides, e.g., amphotericin B and miconazole (MCZ), stabilized hydrophobic drug particles and were effective in vivo. Here, the interaction between MCZ and DODAB BF is evaluated from determination of BF loading capacity and effects of drug-to-lipid molar proportion (MP) on particle size, zeta potential and gel-to-liquid-crystalline phase transition T m . DODAB BF solubilized MCZ over a range of MP. BF loading capacity was 0.5 mM MCZ at 5 mM DODAB. Above this limit, the drug aggregated in the dispersion. At pH 6.3, BF zeta potentials decreased with MP, suggesting insertion of deprotonated drug into the bilayer. MCZ optical spectra in BF were similar to those in best organic solvent, confirming drug solubilization. At MP ⩽ 1 : 10 , BF T m remained unchanged, suggesting drug capture at BF hydrophobic edges. At MP ⩾ 1 : 10 , T m decreased, showing MCZ insertion into DODAB bilayer. However, drug was expelled from the bilayer core upon lowering temperature. Minimal fungicidal concentrations against C. albicans were synergically reduced by 10 times for drug/BF.
Keywords: Miconazole; Dioctadecyldimethylammonium bromide; Sodium dihexadecylphosphate; Bilayer fragments; Fungicidal activity; Candida albicans;

Low-pressure argon adsorption assessment of micropore connectivities in activated carbons by T. Zimny; F. Villieras; G. Finqueneisel; L. Cossarutto; J.V. Weber (248-251).
Low-pressure argon adsorption has been used to study the energetic distribution of microporous activated carbons differing by their burn-off. The collected isotherms were analyzed using the derivative isotherm summation method. Some oscillations on the experimental curves for very low partial pressures were detected. The results are analyzed and discussed according to the literature and could be attributed to local overheating caused by spontaneous mass transfer of argon through constrictions between former pores and the new opening pore or deadend pores. We used the dynamic character of the experimental method and mainly the discrepancy of the quasi-equilibrium state to deduce key parameters related to the porosity topology.
Keywords: Activated carbon; Surface heterogeneity; Micropore connectivity; Low-pressure argon adsorption;