Distinct diffusion in macromolecule-solvent mixtures.

The specificity of interactions between pairs of mols. cannot be explicitly given by exptl. transport coeffs. such as intra- or mutual diffusion coeffs. But a microscopic interpretation of the transport properties exists, where distinct diffusion coeffs. (DDCs) are related to preferential, correlated motion among distinct mols. Since in general the DDCs do not play the role of an indicator for mol. self-assocn. phenomena if not compared with some appropriate std., a DDC of hard spheres at the second order of vol. fraction as new std. coeff. is proposed. The theor. anal. based on the DDC was designed to study intermol. interactions between macromols. and solvent. Comparisons of the non-ideal with previous ideal ref. states were carried out, and their combined use is shown to reinforce information conveyed by the usual velocity correlation anal. The comparison of novel hard sphere stds. with real DDCs, corresponding to an homologous chem. series of poly(ethylene glycol)-water mixts., describes polymer-solvent mixt. in a dil. and semi-dil. regime.