Capillary osmosis through porous partitions and properties of boundary layers of solutions

According to the theory of one of the authors, when the adsorption layer on a solid surface in contact with a solution is mobile, the gradient of concentration of the solution along the solid surface causes capillary-osmotic slip in addition to diffusional flow of the liquid. In the case of porous partitions separating solutions of different concentrations, slip along the pore walls causes convective transfer of the solution, i.e., capillary osmosis. A special unit has been constructed to study this phenomenon and the velocity of capillary-osmotic flow is measured with the aid of radioactive indicators. Formulas are derived for the arising capillary-osmotic flow of substance, making it possible, by introducing a correction for the diffusional flow, to calculate the velocity of capillary-osmotic slip.

There is usually on the surface of glass both a double layer due to the dissociated part of the solution, and an adsorption layer of the undissociated part of the solution. Thus, under real conditions there are flows due both to the double layer on the glass surface and to the mobile part of the adsorption layer of the undissociated part of the solution. Knowing the values of the capillary-osmotic slip and the zeta-potential, one can calculate which of these processes predominates. For this purpose capillary-osmotic flows through Shott filters of certain aqueous solutions and nonaqueous mixtures are measured simultaneously with their zeta-potentials, on the surface of Shott glass. It is shown that for these solutions the flows caused by the double layer at the glass surface are small compared to those due to the mobile part of the adsorption layer of the undissociated part of the solution.

Expressions are obtained for positive and negative adsorption of the undissociated part of the solution, relating the capillary-osmotic velocity to the constant of effective molecular attraction between the dissolved molecules and the glass.

Hence, the constants of molecular attraction between the molecules and the glass, and the average distance between the solute molecules and the plane of slip are calculated from experimental results for the solutions studied.

Thus, the experimental method and calculations proposed may be used for analyzing the structure of adsorption layers at solid-solution interfaces.     

Tuning the mechanical properties in model nanocomposites: Influence of the polymer‐filler interfacial interactions

This article presents a study of the polymer‐filler interfacial effects on filler dispersion and mechanical reinforcement in Polystyrene (PS)/silica nanocomposites by direct comparison of two model systems: ungrafted and PS‐grafted silica dispersed in PS matrix. The structure of nanoparticles has been investigated by combining small angle neutron scattering measurements and transmission electronic microscopic images. The mechanical properties were studied over a wide range of deformation by plate–plate rheology and uni‐axial stretching. At low silica volume fraction, the particles arrange, for both systems, in small finite size nonconnected aggregates and the materials exhibit a solid‐like behavior independent of the local polymer‐fillers interactions suggesting that reinforcement is dominated by additional long range effects. At high silica volume fraction, a continuous connected network is created leading to a fast increase of reinforcement whose amplitude is then directly dependent on the strength of the local particle–particle interactions and lower with grafting likely due to deformation of grafted polymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Tuning the interfacial properties of grafted chains with a pH switch

Environmentally responsive, water-soluble polymers have a wide variety of uses ranging from drug delivery to viscosity modifiers. Their utility lies in the ability to use environmental perturbations to dramatically alter the material properties. Here, we describe the interfacial properties of a hydrophobically modified copolymer of N-isopropylacrylamide and glycinylacrylamide (NIPAM-N-Gly-(C18)2), which is both temperature and pH responsive. Direct force measurements quantified the substantial pH-dependent change in the molecular properties of end-grafted NIPAM-N-Gly-(C18)2 monolayers. At pH 8.0, where the glycine side chains are ionized, the polymers exhibit stereotypical polyelectrolyte behavior. Side chain neutralization at pH 5.0 causes a substantial decrease in the film thickness, and the polymer films adhere strongly. The adhesion is presumably through H-bonding between the glycine side chains. Our findings revealed the likely molecular basis of pH-dependent changes in the copolymer films and identified clear design criteria for tuning the interfacial properties of these polymer films.     

Active control of interfacial properties

Recent studies aimed at establishing principles for active control of the physicochemical properties of interfaces have made substantial progress towards demonstrating spatial and temporal control of interfacial properties of both liquids and solids. Light-active and redox-active surfactants have been shown to permit large (>20 mN/m) and reversible changes in the surface tensions of liquids on time-scales of seconds. These changes can be directed to localized regions of liquids with sub-millimeter spatial resolution, thus providing new means to create controlled gradients in surfactant-based properties of liquids (e.g. gradients in surface tension). Progress has also been reported in the electrowetting of liquids on the surfaces of solids, although it is still not possible to use an external electric field to cause an aqueous solution to wet a hydrophobic surface.     

Thermophysical properties of interfacial layer in nanofluids

Although recent experiments have revealed that nanofluids have superior thermal conductivities to base fluids, the inherent physics are not fully understood. In this study, an interfacial layer, competing with Brownian motion as a corresponding mechanism, is conceptually connected with the surface-charge-induced electrical double layer. By applying colloidal science, the first explicit equations for the thickness and thermal conductivity of the layer are obtained. A fractal model including the new concept of the layer is developed. The model predictions are compared with experimental data for effects of pH, temperature, volume fraction, and primary particle size of CuO-water nanofluids.     

On the dissolution and interfacial properties of hydroxyapatite

An acid—base cyclic titration procedure has been developed to elucidate the dissolution behavior of hydroxyapatite. The effects of various inorganic acids, stannous fluoride and citric acid on the solubility of hydroxyapatite are interpreted in terms of the cyclic titration results and electrophoretic mobility measurements. This study confirms the previous results that fluoride ions are essential to achieve any significant reduction in acid dissolution. Although both the fluoride and citrate ions make the zeta potential of hydroxyapatite highly negative, the fluoride reduces the solubility whereas the citrate enhances the dissolution. The differences are explained in terms of the manner in which the complex ions adsorb. The influence of other reagents on dissolution is less significant.     

Kinetics of iodine mass transfer under the conditions of spontaneous interfacial convection through a planar phase boundary

The iodine mass transfer under the conditions of interfacial instability was studied. The influence of the initial iodine concentration on the mass transfer intensity under the conditions of spontaneous interfacial convection was examined. The mass fluxes were calculated for the diffusion and spontaneous interfacial convection modes. The dependence of the mass fluxes on the initial iodine concentration was determined.     

Electrophoresis of a charged colloidal particle in porous media: boundary effect of a solid plane

Electrokinetic treatments such as the electrophoretic technique have been applied successfully to various soil remediation and contaminant removal situations. To understand further the fundamental features involved, the electrophoretic motion of a charged particle in porous media is investigated theoretically in this study, focusing on the boundary effect of a nearby solid plane toward which the particle moves perpendicularly. The porous medium is modeled as a Brinkman fluid with a characteristic screening length (λ(-1)) that can be obtained directly from the experimental data. General electrokinetic equations are used to describe the system and are solved with a pseudospectral method based on Chebyshev polynomials. We found that the particle motion is deterred by the boundary effect in general. The closer the particle is to the boundary, the more severe this effect is. Up to a 90% reduction in particle mobility is observed in some situations. This indicates that a drastic overestimation (10-fold!) of the overall transport rate of particles may occur for large-scale in situ operations in porous media, such as soil remediation utilizing large planar electrodes, should a portable analytical formula valid for bulk systems only be used. Correction factors for various situations in porous media are presented as convenient charts with which to aid engineers and researchers in the field of environmental engineering, for instance, as a realistic estimation of the actual transport rate obtainable. In addition, the results of present study can be applied to biomedical engineering and drug delivery as well because polymer gels and skin barriers both have a porous essence.     

The interfacial dilational properties of hydrophobically modified associating polyacrylamide studied by the interfacial tension relaxation method at an oil-water interface

The interfacial dilational viscoelastic properties of hydrophobically associating block copolymer composed of acrylamide (AM) and a low amount of 2-phenoxylethyl acrylate (POEA) (<1.0 mol%) at the octane-water interfaces were studied by means of the interfacial tension relaxation method. The dependencies of interfacial dilational elasticity and viscous component on the dilational frequency were investigated. The interaction of hydrophobically associating block copolymer [P(AM/POEA)] with sodium dodecyl sulfate (SDS) has been explored. The results show that at lower frequency, the dilational elasticity for different concentration copolymer is close to zero; at higher frequency, the dilational elasticity shows no change with increased frequency; At moderate frequency (10(-3)-1 Hz), the dilational elasticity decreased with a decrease in the dilational frequency. The results show that the hydrophobic groups of [P(AM/POEA)] chains can be associated by inter- or intrachain liaisons in water solution. The dilational viscous component for P(AM/POEA) comes forth a different maximum value at different frequencies when the polymer concentration is different. It is generally believed that the dilational viscous component reflects the summation of the various microscopic relaxation processes at and near the interface and different relaxation processes have different characteristic frequencies. The spectrum of dilational viscous component may appear more than once maximum values at different frequencies. The influence of SDS on the limiting dilational elasticity and viscous component for polymer solution was elucidated. For 5000 ppm polymer solution, the limiting dilational elasticity decreased with an increase in SDS concentration. The dilational viscous component passed through a maximum value with a rise in the dilational frequency, which appeared at different frequency when SDS concentration is different; and the higher is the concentration, the lower is the dilational frequency. It can be explained that macromolecules may be substituted by SDS molecules in the interface and the interaction of molecules decrease, which makes the limiting dilational elasticity decrease. For 200 ppm polymer solution, the limiting dilational elasticity increased firstly and then decreased with SDS concentration increasing. This may be explained that the interfacial polymer concentration is so low that SDS molecules absorbed in the interface dominate dilational properties of the interfacial film even at very low SDS concentration. However, SDS molecules can gradually substitute the polymer molecules in the interface with a rise in SDS concentration, which results in the decrease in the limiting dilational elasticity.     

不同稀释剂中HDEHP的界面性质研究

用滴体积法研究了HDEHP在不同稀释剂-0.05mol.dm^-^3(N2, Na2)SO4(pH=2.40)体系中的界面性质, 认为吸附于液-液界面的是单体HDEHP分子, 得到了各体系中HDEHP的Cmin, Tmax, Ai以及△Gad等界面吸附参数。HDEHP在不同稀释剂体系中的界面活性顺序为: 脂肪烃>芳香烃>氯仿>甲基异丁基酮, 这种变化主要是在体相中和界面上稀释剂与萃取剂、界面上的萃取剂及稀释剂与界面层水之间分子间相互作用的结果。同时讨论了HDEHP在不同稀释剂中的萃取动力学机理。     

Gravimetric characterisation of the surface properties of a porous drug carrier

The gas adsorption method is the most common means to characterise the topology of solid surfaces with regard to its use as an adsorbent. Adsorption isotherms are determined advanta-geously using a vacuum microbalance: Thermogravimetric techniques allow the observation of sample degassing and its optimization. The dry mass is determined in situ, the mass of gas adsorbed is measured directly and different gases can be used without calibration. From the isotherm the pore size distributions, specific surface area, fractal dimension and density can be derived. Commercially available gravimetric sorption apparata and vacuum balances as well as software for data evaluation are reviewed in tables. The sorption analysis of an aluminum oxide is presented. The porous material was used as a matrix for a slow drug release.     

Tailoring of interfacial properties by ionic liquids in a fluorinated matrix based nanocomposites

Different ionic liquids based on alkyltriphenylphosphonium and imidazolium-functionalized either with two alkyl chains or with a fluorinated chain have been synthesized and used as interfacial agents for the layered silicates. The effect of the chemical nature of the organic cation on the morphology and the physical properties of the polyvinylidene fluoride (PVDF) nanocomposites has been studied. The influence of ionic liquids on polymorphic crystalline forms, i.e. α and β phases of the polymer matrix was discussed.     

A monolayer model of the interfacial region of microemulsions

Mixed monolayers of tetradecanol and oleic acid at the water-air interface were studied to provide a static related structure featuring the interface between water and oil of water-dodecane microemulsions.The films of pure components as a function of temperature show a strong area contraction between 25 ° and 30 °C, caused by a change in the head groups hydration. This agrees with similar discontinuities found for some properties of the microemulsion in the same temperature range. At the water-air interface, the composition range of tetradecanol/oleic acid mixtures with the highest thermodynamic stability corresponds to the same stability range of the water-in -dodecane-potassium oleate microemulsions.Adsorption isotherms of tetradecanol and hexanol at the dodecane-water interface were studied to compare the surface behaviour of the two alcohols; the results indicate that the two alcohols have very similar two-dimensional surface phases and adsorption energies.     

Vapor-liquid interfacial properties of rigid-linear Lennard-Jones chains

We have obtained the interfacial properties of short rigid-linear chains formed from tangentially bonded Lennard-Jones monomeric units from direct simulation of the vapour-liquid interface. The full long-range tails of the potential are accounted for by means of an improved version of the inhomogeneous long-range corrections of Janec?ek [J. Phys. Chem. B 110, 6264-6269 (2006)] proposed recently by MacDowell and Blas [J. Chem. Phys. 131, 074705 (2009)] valid for spherical as well as for rigid and flexible molecular systems. Three different model systems comprising of 3, 4, and 5 monomers per molecule are considered. The simulations are performed in the canonical ensemble, and the vapor-liquid interfacial tension is evaluated using the test-area method. In addition to the surface tension, we also obtain density profiles, coexistence densities, critical temperature and density, and interfacial thickness as functions of temperature, paying particular attention to the effect of the chain length and rigidity on these properties. According to our results, the main effect of increasing the chain length (at fixed temperature) is to sharpen the vapor-liquid interface and to increase the width of the biphasic coexistence region. As a result, the interfacial thickness decreases and the surface tension increases as the molecular chains get longer. The surface tension has been scaled by critical properties and represented as a function of the difference between coexistence densities relative to the critical density.     

Foaming and interfacial properties of hydrolyzed beta-lactoglobulin

beta-lactoglobulin (beta-lg) was hydrolyzed with three different proteases and subsequently evaluated for its foaming potential. Foam yield stress (tau0) was the primary variable of interest. Two heat treatments designed to inactivate the enzymes, 75 degrees C/30 min and 90 degrees C/15 min, were also investigated for their effects on foam tau0. Adsorption rates and dilatational rheological tests at a model air/water interface aided data interpretation. All unheated hydrolysates improved foam tau0 as compared to unhydrolyzed beta-lg, with those of pepsin and Alcalase 2.4L(R) being superior to trypsin. Heat inactivation negatively impacted foam tau0, although heating at 75 degrees C/30 min better preserved this parameter than heating at 90 degrees C/15 min. All hydrolysates adsorbed more rapidly at the air/water interface than unhydrolyzed beta-lg, as evidenced by their capacity to lower the interfacial tension. A previously observed relationship between interfacial dilatational elasticity (E') and tau0 was generally confirmed for these hydrolysates. Additionally, the three hydrolysates imparting the highest tau0 not only had high values of E' (approximately twice that of unhydrolyzed beta-lg), they also had very low phase angles (essentially zero). This highly elastic interfacial state is presumed to improve foam tau0 indirectly by improving foam stability and directly by imparting resistance to interfacial deformation.     

Synthesis and interfacial properties of sophorolipid derivatives

Biosurfactants made by fermentation from renewable resources provide “environmental friendly” processes and products. A natural sophorolipid mixture was produced by the yeast Candida bombicola when cultured on glucose and oleic acid. The sophorolipid mixture was chemically modified to form the corresponding sophorolipid alkyl (methyl, ethyl, propyl, and butyl) esters by reaction with the corresponding sodium alkoxides. Interfacial properties of these surfactants, such as surface tension reduction, aggregation, and adsorption, were systematically studied. It was found that the critical micelle concentration of sophorolipid esters decreases to about 1/2 per additional one CH₂ group to the alkyl ester moiety. Interestingly, these surfactants were found to adsorb strongly on alumina but weakly on silica. They have properties that make them attractive candidates for uses in detergents, cosmetics, soil remediation, and enhanced oil recovery.     

Changes in interfacial properties of alpha-synuclein preceding its aggregation

Parkinson's disease (PD) is associated with the formation and deposition of amyloid fibrils of the protein alpha-synuclein (AS). It has been proposed that oligomeric intermediates on the pathway to fibrilization rather than the fibrils themselves are the pathogenic agents of PD, but efficient methods for their detection are lacking. We have studied the interfacial properties of wild-type AS and the course of its aggregation in vitro using electrochemical analysis and dynamic light scattering. The oxidation signals of tyrosine residues of AS at carbon electrodes and the ability of fibrils to adsorb and catalyze hydrogen evolution at hanging mercury drop electrodes (HMDEs) decreased during incubation. HMDEs were particularly sensitive to pre-aggregation changes in AS. Already after 1 h of a standard aggregation assay in vitro (stirring at 37 degrees C), the electrocatalytic peak H increased greatly and shifted to less negative potentials. Between 3 and 9 h of incubation, an interval during which dynamic light scattering indicated AS oligomerization, peak H diminished and shifted to more negative potentials, and AS adsorbability decreased. We tentatively attribute the very early changes in the interfacial behavior of the protein after the first few hours of incubation to protein destabilization with disruption of long-range interactions. The subsequent changes can be related to the onset of oligomerization. Our results demonstrate the utility of electrochemical methods as new and simple tools for the investigation of amyloid formation.     

Nonlinear electrical grain boundary properties in proton conducting Y-BaZrO3 supporting the space charge depletion model

The overall proton conductivity of polycrystalline acceptor-doped BaZrO(3) is limited by the high resistivity of its grain boundaries. To investigate the nature of the electrical response of the grain boundaries as a function of the DC bias, Y-doped BaZrO(3) ceramics with a very large grain size (up to 200 μm) have been prepared in an infrared image furnace. The grains are so large that even individual grain boundaries can be addressed by microelectrodes. DC voltage-dependent resistance and capacitance of the grain boundaries are discussed in terms of the space charge model. The results corroborate carrier depletion (OH(O)˙, h˙, V(O)˙˙) as origin of the pronounced grain boundary resistance. This picture fits well into the space charge scenario found for various related oxide materials, and leads to strategies for improving grain boundary conductivity.