On the interaction between macroions in solution at infinite dilution

The pair interaction potential for charged macromolecules in solution is calculated from the Ornstein-zernike equation with MSA-closure for the salt-ion/salt-ion and salt-ion/macroion interaction, and HNC-closure for the macroion/macroion interaction. Two different limiting cases are considered: low salt-ion concentration or zero hardcore volume of the macroion. It is found that if the Debye screening length is much larger than the smallest linear dimension of the macroion, the potential is simply a superposition of point-point interaction potentials (screened Coulomb potentials).     

Melittin and ionic surfactant interactions in monomolecular films

The interaction between the anionic and cationic surfactants with Melittin spread monolayers at the air-water interface was investigated. The addition of anionic Cl^–, under the films of Melittin gives rise to a change in both surface pressure and surface potential. These interactions are different when surfactants are present, due to specific interactions between Melittin and the ionic-surfactants.     

Interaction between an ion-penetrable particle and a solid particle. II. Criteria for heterocoagulation

The potential energy of the total interaction between two spherical colloidal particles of different nature is calculated, i. e., of an ion-penetrable particle and an ion-impenetrable solid particle having a constant surface potential or constant surface charge density. The criteria for heterocoagulation are derived. The obtained results suggest a possibility of selective coagulation in the mixed system.     

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.     

Monolayers of methacrylic polymers containing aromatic groups

Monolayers of poly-methacrylates containing either aromatic or linear side groups were studied at the air-water interface. The aim of the work is to define the role of the aromatic group in determining the interfacial distribution and orientation of these polymers. Surface pressure measurements show that all the polymers give stable expanded monomolecular films between 288 K and 308 K temperature range.Surface potential and ellipsometric measurements show that both aromatic and aliphatic polymers are in an almost horizontal conformation at the liquid-air interface. From a comparison of the experimental isotherms with Huggins' theory, it was deduced that no preferential interactions exist between benzene rings in the film. In contrast, preferential attractive energies are observed for n-alkylmethacrylates.Further information on the state of the collapsed film was obtained from electron scanning micrographs.     

Polymethylmethacrylate and stearic acid compatibility in monolayers

Mixed monolayers of polymethylmethacrylate (PMMA) and stearic acid (SA) on substrates with different pH are examined at 25 °C.The spreading isotherms of the pure components and their mixtures in different molar ratios indicate a critical pH value of the support, above which the components are miscible.This limiting pH value, which is confirmed also by surface potential measurements, allows a sufficient ionization of the carboxilic acid.This study was supported by CNR and MPI.     

Potential distribution across membranes with surface-charge layers. Effects of ionic solubility

A model is presented for the potential distribution across a charged membrane. The membrane-fixed charges are assumed to be distributed through a surface layer of non-zero thickness on the membrane. We treat the surface layer as a different phase from the surrounding solution phase. The potential arises from the membrane-fixed charges and from different solubilities of positive and negative electrolyte ions in the two phases. Equations are presented for the potential distribution, which involve the partition coefficients of electrolyte ions and the relative permittivity of the surface layer.     

Estimation of the critical micelle concentrations and the aggregation numbers of sodium alkyl sulfates by capillary-type isotachophoresis

The analytical procedure for the separation and quantification of bulk and micellar phases for sodium alkyl sulfates has been investigated by a capillary-type isotachophoresis using a potential gradient detector. Monomer solutions were distinguished from micellar solutions at pH 5.5–6.0; hydrochloric acid — L-Histidine mixture was used as the leading electrolyte and 2-(N-Morpholino) ethanesulfonic acid as the terminating electrolyte.The potential unit value (PU value) due to the monomer solutions was larger than that due to the micellar solutions. The zone length due to monomer solutions increased with increasing concentration of surfactant until a given concentration (CMC); beyond this point the values became constant. On the other hand, the zone length due to micellar solutions increased from this point. We report an applicability of capillary-type isotachophoresis to determination of the CMC's and aggregation number for various sodium alkyl sulfates.     

Water vapor adsorption and capillary reactions of silicates

States of disperse silicate systems classified according to their fundamental morphological types were represented by a ternary diagram. Water vapor equilibria of various silicate samples were investigated by energy levels, by equivalent pore number of potential bands determined from adsorption potential curves. The silicate adsorbents were characterized by adsorption energy, equipotential surface area and specific capillary. Electrical properties of adsorbents depending on their water contents were examined. Changes of adsorption properties of mechanical, thermal and by ion exchange treated silicates were observed. Electrical properties of adsorbents depending on their humidity were examined. Capillary reactions were observed causing irreversible adsorption-desorption cycles.     

The effect of water on the zeta potential of chromium dioxide in tetrahydrofuran

Experiments have been performed to determine the effect of water on dilute suspensions of CrO₂ in tetrahydrofuran (THF). The effect of water in the solvent as well as on the particle surface has been investigated using electrokinetic and dispersion stability measurements. Results of these investigations have shown that the zeta potential of dried CrO₂ (physisorbed water removed) in THF is positive and is dependent on the water content in THF. The zeta potential exhibits a maximum at about 1,800 ppm water. Good correlation also exists between the electrokinetic and dispersion stability measurements.     

On Tanaka-Fillmore's kinetics swelling of gels

Tanaka and Fillmore treated the swelling of a gel as a process where a crosslinked polymer network having been initially under uniform stress is expanded by osmotic pressure, sucking up the surrounding fluid medium. We point out that their physical reasoning is unnatural and leads to an unacceptable conclusion; we propose a more sound approach to the same problem. Our treatment assumes that the gel network is extended not by the osmotic pressure of the gel, but rather by the swelling pressure which is generated by the excess fluid penetrating in against the real nature of a polymer network that tends to shrink. The diffusion equation of the fluid, hence, plays a dominant role and gives the distribution of fluid concentration in contrast to Tanaka-Fillmore's scheme. The expression for the distribution of local strain in a spherical gel is deduced from the relation of mechanical balance between two forces, the one is due to the elasticity of the network and the other due to the gradient in the chemical potential of the fluid. The results obtained have forms analytically similar to Tanaka-Fillmore's, but are differ in the physical meanings.     

Characteristics of mixed bilayers of surfactants formed on alumina

The interaction between hydrocarbon and fluorocarbon surfactants on-alumina has been studied through the dispersion behavior of-alumina. When a low concentration of anionic hydrocarbon or fluorocarbon surfactant as a first additive is added to positively charged alumina, the alumina flocculates. The flocculated alumina redisperses upon addition of different surfactant from the first one by the manner that the hydrophobic parts of hydrocarbon and fluorocarbon surfactants are in contact with hydrophobic parts of the first surfactants and the hydrophilic polar groups direct out to liquid phase, resulting in the formation of mixed bilayers on the alumina. From the measurements of mean particle size, zeta potential of the alumina, and adsorbed amount of surfactants, the mixed bilayers consisting of anionic fluorocarbon-noniomc hydrocarbon surfactants and of anionic fluorocarbon-noioic hydrocarbon ones are found to be formed more preferentially than anionic hydrocarbon-anioic fluorocarbon surfactants. The property of the mixed bilayer on the alumina is also discussed using the fluorescence spectra of pyrene.     

Behavior of pure and mixed DPPC liposomes spread or adsorbed at the air-water interface

Liposomes from pure dipalmitoylphosphatidylcholine (DPPC) and mixed DPPC: distearoylphosphatidylcholine (DSPC): soybean lecithin (SL) prepared by the Bangham method with sonication were dispersed into solution or spread at the interface and the kinetics of the surface film formation was studied by measuring and recording the evolution of superficial tension, surface potential, and superficial (¹⁴C labeled) DPPC density.A simple theoretical approach can describe these kinetics by two processes: irreversible diffusion of closed vesicles into or from the bulk phase, and irrevers ible transformation of closed spherical vesicles into destroyed ones which form the surface film. Diffusion controls the phenomenon for small initial amounts of liposomes.Transformation controls the phenomenon for important initial amounts of liposomes. The kinetic constant of the transformation,K, does not depend on the technique used to form the surface film (spreading or adsorption).The equilibrium and rheological properties of surface films formed after liposome spreading are compared to those of monolayers     

Study of the thermodynamics of adsorption of hydrolyzed modified polyacrylnitrile

The thermodynamics of adsorption has been studied of hydrolyzed modified polyacrylnitrile (HMP) in water solutions with a concentration ranging from 0.25 g/l to 2.00 g/l on bleached sulphate and unbleached and bleached sulphite celluloses at temperatures of 0, 20, 40, and 60 C.It has been established that with the rise in temperature, the amount of adsorbed polymer —(HMP) decreases. The values of the enthalpy change are negative and show a linear decrease with the increase in the amount of adsorbed polymer. The adsorption equilibrium is defined by the logarithmic isotherm of Tjumkin, valid for uniform heterogeneous surfaces.With the increase in the amount of adsorbed HMP the values of the entropy change become negative and linearly decrease. A compensation effect has been noticed which results from the simultaneous action of the entropy and energy factors.The values of the change of the chemical potential for the three types of cellulose are negative and linearly decrease with the increase in the amount of adsorbed HMP and with the rise in temperature.     

Interaction of nitrophenols with lipids at the air/water interface

The uptake of ortho and para nitrophenol to charged and neutral lipid monolayers spread at the air/solution interface was studied by reflection spectroscopy. The adsorption characteristics of the two nitrophenols have been studied by measuring the surface pressure and surface potential as a function of molecular area of the different lipid monolayers in the presence of nitrophenols in the subphase. The results have been interpreted in terms of the electrostatic interaction between the negatively charged dissociated phenolate ions and the positively charged head group of dioctadecyldimethylammonium bromide monolayers.     

Diffusion of single elements and steric limitations in kinetic theory of nucleation and crystallization

Translational and rotational diffusion equation of single elements in solution in the external orienting potential forces has been formulated. The equation should govern long-range diffusion effects in the kinetics of nucleation and crystal growth. Boundary conditions, adequate to the reversible reaction of cluster growth typical for kinetic model of nucleation and accounting for steric limitations, has been proposed. Uniaxial single elements in uniaxial orienting force field are considered.Depression of the concentration of single elements at the cluster boundary as controlled by kinetic factors, is predicted i. e., chemical rate constants, finite translational and rotational diffusion, supercolling, and steric limitations. Effective rate constants, controlled by long-range diffusion of single elements at steric limitations present, have been used. Two dimensionless kinetic factors (i. e., reduced addition-reaction rate constant and reduced rotational diffusion constant), supercooling, and steric tolerance anlge range, control process kinetics and distribution of single elements in the cluster's surroundings. Rate reduction factor responsible for the effects of long-range diffusion at steric limitations present is defined and applied for kinetic models of nucleation and crystal growth in unoriented and oriented systems.Computation examples are performed for a wide range of the model variables, and rate reduction effects of several orders of magnitude are predicted. The dominating role ranges of particular model variables, i. e., kinetic, thermodynamic, or steric variables, are discussed.     

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.