A generalization of the Rouse-Zimm model

The idea of consistently averaging the hydrodynamic interaction and its various consequences for Hookean dumbbells are reviewed. For long chains this idea can be used to generalize the Rouse-Zimm model for polymer solutions. Unlike the usual Rouse-Zimm model, the new model for steady shear flow predicts a nonzero second normal stress coefficient and shear rate dependent material functions. In the limit of long chains, the viscosity and the normal stress coefficients are universal functions of the reduced shear rate.This paper was presented at the Frühjahrstagung des Fachausschusses Polymerphysik der Deutschen Physikalischen Gesellschaft at Kaiserslautern (West Germany), March 12–14, 1986.     

Interaction between an ion-penetrable particle and a solid particle. 1. Electrical double-layer interaction

Expressions are derived for the force and potential energy of the electrical double layer interaction between two parallel plates of different nature, i. e., an ion-penetrable plate and an ion-impenetrable plate. The latter may have either constant surface potential or constant surface charge density. It is shown that when the ion-impenetrable plate has a constant surface potential, the interaction force may, under certain conditions, become attractive even if the surface potentials of the two plates at infinite separation are of the same sign. In contrast, when the ion-impenetrable plate has a constant surface charge density, the interaction force may, under certain conditions, become repulsive even if the two plates at infinite separation are of opposite sign. This means that an ion-penetrable plate shows a dual behavior. That is, under certain conditions, it behaves like a solid plate with constant surface potential or surface charge density, depending on whether it interacts with a solid plate having a constant surface potential or a constant surface charge density.     

Potential theory in the problems of interfraction at small gap widths. Sphere and flat interface

An asymptotic model is proposed for the flow pattern inside a droplet when a thin liquid layer is formed at its advancing nose; at small gap widths, so far as the substantial part of the flow inside the droplet is concerned, the interface may be regarded as a flat interface. Calculations are made using the classical potential theory. The problem of hydrodynamic interaction is brought to the investigation of an integral equation for the radial velocity a the flat interface. The equation is asymptotically solved for low and high viscosities in the droplet. For these cases, results are also reported about drag force.     

The effect of particle concentration on zeta potential in extremely dilute solutions

The electroporetic mobility of hexadecane particles in water and in very dilute CTAB solutions was measured. The technique of microelectrophoresis was applied. Zeta potential was calculated according to the Hückel formula, applying Henry's correction factors. Electrokinetic charge density was calculated according to the formula used by Delgado et al., and previously discovered empiricaly by Loeb et al. and derived mathematicaly by Ohshima et al. It was found that the particle concentration in emulsion limits their charge in solutions of very low ion concentration (10^–7:10^–6 M), because the greater the particle concentration, the smaller the extent of the ions adsorbed at the surface of one particle. The zeta potential was found to be independent of particle concentration if the ratio of the number of bulk ions to particle number is not lower than 1.6×10⁶. This ratio depends on particle size, and the value 1.6×10⁶ relates to particles of diameter 1.6 m.     

The pH dependence of dispersion of TiO2 particles in aqueous surfactant solutions

The pH dependence of dispersion of titanium dioxide (TiO₂) particles has been examined in the presence of surfactant molecules in water. Whereas particles were dispersed in water at acid and alkaline regions rather than at neutral region, the dispersion was enhanced at neutral region in an aqueous sodium dodecyl sulfate (SDS) solution and at acid and alkaline regions in an aqueous dodecyldimethylamine oxide (C₁₂DAO) solution. Considering the pH dependence of zeta potential, the adsorption models of surfactant molecules on a particle were estimated on the basis of the modes of hemimicelle and double-layer compression. While the particles that adsorbed Al³⁺ were remarkably dispersed around pH 6, their dispersion does not largely depend on pH in the addition of SDS, indicating the adsorption of SDS molecules to form double-layer compression in the whole pH region. Dynamic light-scattering measurement and electron microscopic observation suggested that the particles were dispersed in water as small flocs.     

The effect of carrier solution on the particle size distribution of inorganic colloids measured by steric field-flow fractionation

The number average and the weight average particle diameters for suspended inorganic colloids found by the new technique of steric field-flow fractionation may be successfully used provided that the most suitable carrier solution is selected, in order to minimize the coagulation and adhesion phenomena.In the present work polydisperse, irregular colloidal particles of FePO₄·2H₂O (strengite) were studied. The average particle diameters were found to vary with the electrolyte concentration in the suspending medium. A strong variation of the number and weight average particle diameters was also observed with the quantity of the surfactant added to aquatic medium in order to increase colloidal stability. The influence of the electrokinetic charge of the FePO₄·2H₂O particles in relation to the surface charge of the material of the column employed, on the particle size measured was investigated. The proper carrier solution for minimizing coagulation and adhesion phenomena in the FePO₄·2H₂O colloidal particles was found to contain either 1.5% (v/v) detergent FL-70 and 0.1 MKNO₃ or 0.5% (v/v) detergent FL-70 and 0.033 MNa₂SO₄.     

Some novel crystallization kinetic peculiarities in finely dispersing polymer blends

The morphology and the crystallization of blends of poly(vinylidene fluoride) (PVDF) with polyamide-6 (PA-6), and with poly(butylene terephthalate) (PBTP), were investigated in detail by electron microscopy and by DSC. In some of the blends, the dispersed component exhibits rather small particle sizes and, followingly, a high number density of the dispersed particles which is in the order of magnitude of, or exceeds the number density of the usually nucleating heterogeneities. In these blends, the crystallization of the dispersed component proceeded in two steps, induced by different nucleating species (fractionated crystallization). The nuclei concentrations in the components and the specific interfacial energies of the PVDF nucleation steps were estimated. An unusual type of fractionated crystallization occurs in some cases: matrix and disperse phases crystallize completely coincident due to a specific mutual nucleating efficiency of both components. An estimation of the interfacial energies involved suggests a nucleating activity of PVDF crystals for PA-6. Moreover, a rise of the crystallization temperatures of the PA-6 and PBTP matrix phases is observed that may indicate a migration of nucleating impurities during melt processing from PVDF towards the second component.     

On the collision efficiency approach to flocculation

The collision efficiency approach to flocculation is analyzed on the basis of a model describing the probability of aggregation by polymer bridging. The model allows for the effect of the randomness of distribution of polymer over particles as well as the effect of simultaneous coagulation and weak flocculation. It is argued that the collision efficiency approach is applicable to a rather limited range of experimental systems and provides a qualitative understanding rather than a quantitative theory of the relationship between flocculation and adsorption.     

The rheology and microstructure of charged colloidal suspensions

The effects of electric charge interation and particle correlations on suspension rheology are examined. A one-component fluid analysis using a Smoluchowski equation for the equilibrium structure is applied to charged suspensions of spherical colloids under shear. The frequency dependent modulus and viscosity, predicted as functions of particle and added salt concentrations, are compared with published rheological measurements on model suspensions. Recent improvements in the statistical mechanical theories for the equilibrium microstructure, its nonequilibrium deformation, and the bulk shear stresses are included. The direct electrostatic interaction is found to drive the divergence in the shear viscosity near the liquid-solid phase transition. Extensions of the theory predict the elastic modulus of binary mixtures of charged colloids. Estimates of the primary electroviscous effect, hydrodynamic interactions, and errors in the Yukawa limiting form for the potential and applications of asymptotic theories are presented. Predictions for the rheology based on effective hard-sphere models are found to be reasonable when using a parameter fit from the equilibrium phase behavior. Mean-field mode coupling theories predict larger relaxation times than calculated from the Smoluchowski equation (=SE). A study of binary mixing effects on elasticity shows non-ideal behavior. It is noted that equilibrium structural information can be used to resolve discrepancies between the theoretical predictions and the measured rheology.     

Surface characterization of modified glass fibers by inverse gas chromatography

The dispersive component of the surface free energy _d ^s of glass fibers and their acid-base interaction can be evaluated by the measurement of specific retention volumes of several kinds of probe molecules by use of an inverse gas chromatography. The effect of the treatment of glass fibers with silane-coupling agents was also evaluated. The specific retention volumes of n-alkanes changed linearly with theirC number or vapor pressure. Those of polar molecules varied with their donor number (DN) or acceptor number (AN). The _s ^d values and electron-accepting or donating abilities depended upon the kind of functional groups contained in the coupling agents.     

Gaussian approximation for Hookean dumbbells with hydrodynamic interaction: Translational diffusivity

The recently developed Gaussian approximation for the hydrodynamic interaction is used to discuss the translational diffusivity of polymers in dilute solutions undergoing homogeneous flows. For the Hookean dumbbell model, we derive the diffusion tensors associated with (i) the average polymer velocity caused by external forces; (ii) the mean-square displacement of a single polymer caused by the Brownian forces; and (iii) the polymer mass flux caused by concentration gradients. We discuss the model predictions for these diffusion tensors for steady shear flow in detail.This paper was presented at the Frühjahrstagung des Fachausschusses Polymerphysik der Deutschen Physikalischen Gesellschaft in Hamburg (West Germany), March 14–16,1988.     

Role of electrokinetic phenomena in the preparation of supported metal catalysts

A model accounting for the effect of electrokinetic phenomena on the prepartion of supported metal catalysts by wet impregnation is presented. The model is able to explain the dependence of catalyst distribution profile and loading on the concentration of the impregnant, on the pH and ionic strength of the impregnating solution, as well as on the presence of a co-impregnating species.     

Colloid-chemical properties of ruthenium dioxide in relation to catalysis of the photochemical generation of hydrogen

A colloid of RuO₂, prepared by thermal decomposition of RuCl₃, was characterized with respect to its colloid-chemical properties and assessed as a catalyst for photochemical production of hydrogen. The RuO₂ proved to be unstable towards coagulation, even under conditions of low electrolyte concentration and in the presence of polymers. The sol manifested the same electric double layer characteristics as many other oxide dispersions. The point of zero charge (p.z.c.) in indifferent electrolyte was positioned at pH 5.75.Adsorption of methylviologen (MV²⁺), a commonly used electron relay in photochemical systems, at the RuO₂/solution interface is mainly a result of attractive coulombic interactions (above the p.z.c. of RuO₂). No indications have been found that it adsorbs on RuO₂ under the operational conditions of hydrogen production. In the hydrogen production system, the mass transfer of methylviologen radicals (MV⁺) is a rate-limiting factor. As a function of the methylviologen concentration, the catalytic production of hydrogen passes through a maximum.Dedicated to Professor Dr. Dr. h. c. Armin Weiss on the occasion of his 60th birthday.     

Solutions of alkali soaps and water in fatty acids XIV. TheL 2-phase structure in light of recent experimental investigations

A scrutiny of some experimental studies of the L₂-phase in the system sodium octanoate-octanoic acid-water published within the last eight years has shown that these experimental findings are not only compatible with the interpretation of the structure of this phase that we have presented in previous papers in this series on the basis of our studies performed in the 1960s, but directly support in several respects, our interpretation. However, some conclusions drawn by other authors from the new findings are not compatible with ours.     

Flow curves of an adsorbed protein layer at the saliva-air interface

At the air-liquid interface of human saliva a protein layer is adsorbed. An apparatus is described with which a flow curve of this layer was measured. In the majority of samples the viscosity of the surface layer changed gradually and could be described by a power-law dependence on the shear rate. The zero-shear viscosity was 1–100 MPa·s. In some saliva samples a sharp yield point was observed.     

Microscopic observation of ordered colloids in sedimentation equilibrium and the important role of Debye screening length. 3. Heavy and monodisperse polystyrene type spheres in aqueous solution of neutral polymers

The ordered structures are observed directly by the metallurgical microscope for the heavy (specific gravity=1.50) and monodisperse polystyrene type spheres in sedimentation equilibrium and in the presence of neutral polymers, polyvinylalcohol (PVA), polyethyleneglycol (PEG), polyvinyl-pyrrolidone (PVP), hydroxypropylcellulose (HPC), and polyacrylamide (PAA_m). The intersphere distances in the ordered lattices decrease by the addition of neutral polymer in the order, PVA < PEG < PVP < HPC < PAA_m. These effects of neutral polymers are reasonably well-explained by the intersphere repulsion from the electrical double layer interaction, which is influenced by the polymer adsorption on the latex surface by the hydrophobic and/or dipole-dipole interactions.     

Hemolytic activity of polyoxyethylene cholesteryl ethers

Hemolytic activity of nonionic surfactants, polyoxyethylene cholesteryl ethers, C₂₇H₄₅O(CH₂CH₂O) _n H (Chol-E _n ,n=, 25, 30, 50) and polyoxyethylene dihydrocholeseryl ethers, C₂₇H₄₇O(CH₂CH₂O) _n H (DHChol-E _n ,n=15, 30 50) were measured, changing the concentration of surfactant and erythrocyte at 37 °C. Maximum hemolytic activity was observed in these cholesteryl derivatives with 25–30 oxyethylene units. The time course of hemolysis was also measured as a function of the concentrations of surfactant and erythrocyte. Hemolysis started after a certain induction period,, and then apparently proceeded as a first-order reaction with respect to the erythrocyte concentration. The surfactant inducing 50% hemolysis at low concentration had a small value and large rate constant. The maximum amount of adsorption without inducing hemolysis,a ₀, decreased with increasing polyoxyethylene chain length. Chol-E₂₅ has the maximum activity for the solubilization of egg yolk lecithin at 37 °C. Based on these results, the mechanism of hemolysis by these surfactants was quantitatively discussed.     

Polymer adsorption on fine particles; the effects of particle size and its stability

The effects of particle size on polyacrylamide (PAAm,M _w =59×10⁴, 500×10⁴) adsorption were investigated using a series of well-characterized hematite (-Fe₂O₃) dispersions. The -Fe₂O₃ particles with highly monodisperse and nearly spherical shape ranged in radius from 23 nm to 300 nm. the maximum amount of PAAm adsorption (M _m ) in each system, showed a steady increase with decreasing particle radius and was influenced strongly by particle concentrations in the medium. Furthermore, it was realized that the diameter of -Fe₂O₃ particles after treatment with PAAm under different particle concentrations decreased with increasing particle concentration. The relation between particle concentration in the medium and particle size after treatment was also influenced by the medium pH, i.e., at the medium pH close to the isoelectric point of -Fe₂O₃ particles (pH^o=9.2), the particle size after treatment increased with increasing particle concentration. All these results suggest that in the system of ultra-fine particles, the mixing process between particle-particle and polymerparticle will play an important role on the conformation of adsorbed polymer layer.     

Potential theory in the problems of interfraction at small gap widths. A solid sphere and a droplet

A solid sphere approaches a spherical droplet at small gap widths. The radii of the particles are identical. Potential theory is applied and the problem of interaction brought to the solution of an integrodifferential equation for radial velocity at the droplet/ thin layer interface. Asymptotic formulae are reported for interface velocity and drag force for small and large viscosity ratios. The results are compared with the solutions for a solid sphere and flat tangentially mobile interface. Thus, two major effects may be distinguished: opening of the gap and curving of the streamlines inside the droplets. The latter is shown to cause a relative increase in the drag force.     

Acid hydrolysis of carboxymethylcellulose of low degree of substitution

Cotton cellulose was swollen in a sodium hydroxide solution and carboxymethylated by a two-bath method for different periods of time for each process. The kinetics of acid hydrolysis and the crystallinity of the swollen and carboxymethylated samples were measured. The proportion of broken bonds, rate constants for hydrolysis, and permeability of cellulose to hydrolyzing agents were calculated. The susceptibility of glycosidic linkages to acid hydrolysis was improved by carboxymethylation more than by swelling in alkali. The increased accessibility of carboxymethylcellulose to acid was regarded as a consequence of increased intra-and intercrystalline swelling and of the glycosidic bonds' weakness caused by the electron-attracting carboxymethyl group on the C-6 position.