Yoshiyuki Einaga

Thermodynamics of polymer solutions and mixtures

Abstract A review is provided for the present situation concerning theoretical predictions of phase equilibria in polymer solutions. Special attention is paid to ternary systems consisting of two polymers and one solvent or of one polymer and two solvents. A survey of the experimental data on various ternary systems has revealed that phase separation behavior is significantly and subtly affected by three interaction parameters for each pair of components, and that a quantitative description of the phase relations requires a very accurate expression of the interaction parameters as a function of temperature, composition of the system, molecular weight of the polymer, and so forth. One promising approach has recently been developed and is based on classical thermodynamic relations of general validity. This is described in some detail. It will be shown that this approach is useful for the characterization of thermodynamic properties of a given ternary system as a function of all relevant variables, and that it allows for the prediction of phase equilibrium behavior with sufficient accuracy.

Analysis of the dynamic structure factor for semi-dilute solutions of polyisobutylene

The equation for polymer concentration fluctuation derived from Onukis equations of motion is coupled with Onukis postulate for the partial stresses generated by concentration fluctuation to formulate the dynamic structure factor S(q,t) [t is time and q the magnitude of the scattering vector]. The actual calculation is made for systems in which the elastic relaxation modulus L(t) is given by a linear combination of n exponential functions. It is shown that the corresponding S(q,t) consists of n + 1 exponential functions of time, and that the relative strengths and decay rates of these functions are related by a set of algebraic equations to the diffusion coefficient and cooperative diffusion coefficient, as well as the parameters characterizing L(t). These equations for n = 2 are used to analyze dynamic light scattering data on semi-dilute solutions of a polyisobutylene fraction in isoamyl isovalerate (Θ solvent) and n-heptane (good solvent). The results give the instantaneous moduli of the solutions which are well compared with the rubbery plateau moduli from viscoelastic measurements, and the friction coefficients which are identical for both solvents when compared at comparable polymer concentrations.

Size Change of the Wormlike Micelles of Pentaoxyethylene, Hexaoxyethylene, and Heptaoxyethylene Dodecyl Ethers with Uptake of n-Dodecane

Wormlike micelles of the surfactant penta-, hexa-, and heptaoxyethylene dodecyl ethers C12 E5, C12 E6, and C12 E7 were characterized by static light scattering (SLS) and dynamic light scattering (DLS) experiments to examine effects of uptake of n-dodecane on the micellar characteristics. The SLS results have been successfully analyzed by the light scattering theory for micelle solutions to yield the molar mass Mw(c) as a function of concentration c along with the cross-sectional diameter d of the micelle. The apparent hydrodynamic radius RH,app(c) determined by DLS as a function of c has also been successfully analyzed by the fuzzy cylinder theory which (-1). It has been found that the micellar length Lw increases with increasing surfactant mass concentration c and the values of d and lambda(-1) increase with increasing n-dodecane content wd, as in the case of various CiEj micelles containing n-alcohol. On the other hand, the values of Mw, Lw, and RH,app for all the micelles examined decrease with increasing wd contrary to the micelles containing n-alcohol. This finding may be attributed to the fact that the addition of n-dodecane into the micelles weakens hydrophilic interactions among polyoxyethylene chains of the surfactant molecules and water, making the micelles unstable, and then leading them to collapse into smaller micelles.

A Rotational Viscometer Permitting Successive Dilution

The low-shear rotational viscometer of the Zimm-Crothers type was modified so that successive dilution of a given solution can be made in the viscometer, as is the case with the capillary viscometer of the Ubbelohde type. This modification simplifies the process of determining the intrinsic viscosity of polymer solution at zero rate of shear. In the instrument constructed, the rotor is driven by rotating an electrically induced magnetic field whose strength can be changed continuously with the supply of variable electric current, and the range of shear rates from about 0.1 to 10 sec-1 can be studied. The data taken on two polystyrene samples (Mv = 2.28 x 105 and 3.35 x 107) in benzene and one poly-n-hexyl-isocyanate sample (Mv-4.0 x 106) in carbon tetrachloride are illustrated to show the potential of the instrument.

Notes on the formulation of concentration fluctuation in moderately concentrated polymer solutions

Abstract The dynamic structure factor of moderately concentrated polymer solutions is often multimodal, roughly consisting of fast and slow modes. Wangs formulation of concentration fluctuations predicts that the slow mode disappears when the polymer and solvent components have identical partial specific volumes, but the prediction is not supported by the formulation of Onuki (J. Non-crystalline Solids, 1994, 172–174, 1151) and that of Doi and Onuki as well (J. Phys. 11 (Paris), 1992, 2, 1631). The present paper shows that the primary origin of the disagreement is the difference in the basic equations of the two theories, in contrast to the prevailing notion that attributes it to the different constitutive equations assumed by the two theories for the partial stresses generated by concentration fluctuation.