Diffusion coefficient matrix in nonionic polymer-solvent mixtures

Recent predictive equations for evaluating the value of diffusion coefficie nts, developed for two hard sphere-solvent systems, have been extended to n -hard-sphere-solvent systems. This model has been used to predict the diffu sion behavior of nonionic polymer-solvent mixtures as a first-order functio n of volume fraction from the knowledge of the distribution function. Hence , the entire diffusion matrix for polydisperse systems, which include both main- and cross-term diffusion coefficients, has been built up for the firs t time. The main-terms diffusion coefficients D-ii are mostly affected by t he variation in viscosity. The magnitude of the cross-term diffusion coeffi cients D-ij is strictly related to the abundance and diffusivity of solute i and to the molecular volume corresponding to solute j. The predicted diff usion coefficients have been used to calculate the apparent, average diffus ion coefficients, which are compared with the experimental values measured by the Gouy interferometry method in the case of the poly(ethylene glycol) homologous series. The agreement between the calculated and experimental Go uy parameters is good. The cross-term diffusion coefficients are found to b e significant in the calculation of the apparent diffusion coefficient for a polydisperse solute. Some comments on the study of ternary systems contai ning a polydisperse solute are done.