Toshiya Ohtsuki

Studies of Ordered Monodisperse Polystyrene Latexes. I. Shear Ultrasonic Measurements

The rigidity G and the viscosity ? of monodisperse polystyrene latexes were measured by the torsional quartz crystal method at 70 kHz, and an abrupt change in G and ? was found at the order-disorder transition of the latexes. The torsional quartz crystal method was improved for measurements with aqueous conductive samples, and a careful calibration showed that G and ? are obtained if the dielectric constant of the sample is known. In the ordered state of latex with a volume concentration of 9.3%, the apparent rigidity G and the viscosity ? were about 1.5?103 dyne/cm2 and 0.6 cp, respectively, while in the disordered state G was small and ? was 0.95 cp. Ordered latex is a ?crystal? formed by the screened Coulomb repulsion and is a good model not only for crystals but also for ordered structures in some biological systems.

Studies of Ordered Monodisperse Latexes. III. Viscoelasticity and Flow Properties

The viscoelastic behaviour at 40 kHz and the steady flow properties of monodisperse polystyrene latexes, i.e. aqueous suspensions of charged polystyrene spheres, were measured through an order-disorder transition as varying the salt concentration in the solvent and the volume fraction of spheres. A latex in the ordered lattice structure showed the rigidity of about 103 dyn/cm2 and the yield stress of about 1 dyn/cm2, which indicates that the ordered latex is a crystal in view of the mechanical properties. The ratio, 10-3, of the yield stress to the rigidity suggests a dislocation mechanism of the plastic flow of the ordered latex.

Diffusion coefficients of interacting Brownian particles

Starting from a N‐particle diffusion equation, the effective particle (self‐) and concentration diffusion coefficients of interacting Brownian particles are studied theoretically. These two diffusion coefficients defined by distinct ways are different for interacting systems. By taking into account both potential and hydrodynamic interactions, the expression for the frequency‐dependent particle diffusion coefficient exact to linear order in number density is derived. Detailed calculations of both diffusion coefficients are performed for model systems of hard spheres with a repulsive or an attractive long‐range potential. The effects of potential and hydrodynamic interactions on these two diffusion coefficients are clarified. The velocity autocorrelation function is also calculated and non‐Markovian behaviors are discussed.

Studies of Ordered Monodisperse Latexes. II. Theory of Mechanical Properties

The electrostatic potential around a particle in an ordered latex under a deformation is numerically calculated form the nonlinear Poisson-Boltzmann equation by an eccentric cell model. The static rigidity of an ordered latex and the order-disorder Lindemanns law of the crystal melting are obtained from the calculated potential. The calculated phase diagram agrees with the experimental phase diagram of Hachisu et al. The Debye-Huckel approximation turns out to be invalid at low ionic concentrations. On the basis of a two-continua model and the calculated static rigidity, propagation of shear waves in an ordered latex is studied and the existence of two kinds of modes is shown. The dynamical complex rigidity is calculated from the mechanical impedance at an oscillating plate. The results agree with the experiment reported in a previous paper.

Studies of Ordered Monodisperse Latexes. IV. Mechanism of Ordering

The order-disorder phase transition of aqueous suspensions of charged polystyrene spheres was studied both experimentally and theoretically. Phase diagrams of four kinds of samples with different surface charge numbers were determined from the observation of disappearance of the characteristic iridescence in the ordered state. The ordered phase appeared in the large volume fraction and low salt concentration regions. The ordered region became larger according to the surface charge number increase. On the basis of Lindemanns law, phase diagrams were also obtained theoretically. The theory reproduced quantitatively the experimental phase diagrams of all the samples used. The applicability of the Debye-Huckel approximation was discussed and the evaluation of the static rigidity reported in a previous paper [Jpn. J. Appl. Phys.: 19 (1980) 439] was improved.

Dynamical properties of strongly interacting Brownian particles: III. Binary mixtures

Abstract A kinetic theory developed in two preceding papers is extended to investigate dynamical properties of binary mixtures of Brownian particles strongly interacting with each other via potential forces. A formalism to calculate the dynamic shear viscosity of the system and the self-diffusion coefficient of each particle is constructed on the basis of the superposition approximation for the three-particle distribution function. Explicit calculations are carried out for screened Coulomb systems and the effects of mixing are clarified. In particular, the shear viscosity turns out to decrease remarkably upon mixing.

Dynamical properties of strongly interacting Brownian particles: II. Self-diffusion

The self-diffusion process of Brownian particles is theoretically investigated for concentrated systems in the presence of strong potential interactions between particles. Starting from an N-particle diffusion equation, a formalism is developed to calculate the self-diffusion coefficient and the velocity autocorrelation function on the basis of the superposition approximation for the three-particle distribution function of non-equilibrium states. Explicit calculations are carried out for model systems of hard spheres with a screened Coulomb potential. Calculated time-dependent self-diffusion coefficients are compared with available data of the Brownian dynamics. Without introducing any phenomenological or adjustable parameters, quantitative agreement is achieved.

Transport properties of non-dilute solutions of strong electrolytes. I. Electric conductivity

Abstract A kinetic theory of the dynamic electric conductivity of strong electrolyte solutions is developed for non-dilute systems up to concentrations around 1 mol/l. On the basis of a primitive model and starting from an N -particle diffusion equation in configuration space, a formalism to calculate the electric conductivity is constructed. Explicit calculations and comparisons with experimental data are carried out for aqueous solutions of NaCl, KCl, NH 4 Cl and BaCl 2 . Without introducing any phenomenological or adjustable parameters, good agreement is achieved.

Generalized diffusion equation of interacting brownian particles

Abstract Macroscopic behavior of a system of brownian particles interacting with each other through potential forces is described by a generalized diffusion equation (GDE) for the density of particles. The diffusion coefficient in the GDE is given by the generalized Stokes—Einstein relation and generally depends on the density. In the presence of long-range interactions, the GDE becomes non-local in space. When a Coulomb interaction exists, the GDE corresponds to an improvement of the Poisson—Boltzmann equation.

Composite torsional quartz transducer for shear ultrasonic measurements of aqueous liquids

A composite torsional quartz transducer has been developed for the shear ultrasonic measurements of aqueous solutions in the frequency range from 10 to 100 kHz. In order to prevent the electric interaction and low contact angle between the transducer and water, a torsional quartz crystal transducer is attached to a fused quartz rod whose surface is partly gilded by evaporation. The accuracy of +/-60 dyn/cm2 for the rigidity and +/-0.03 cP for the viscosity is attained by use of this transducer.