Solvent Self-diffusion, Polymer Nmr Relaxation, and Free Volume in Polymer Solutions

The self-diffusion coefficient of chloroform in poly(isopropyl acrylate-chloroform solutions has been studied as a function of concentration and temperature by using the pulsed-field-gradient spin-echo NMR method. It is found that the self-diffusion coefficient of the solvent can be adequately fitted by using a simple free-volume approach with either a concentration or temperature superposition. It was noted that the free-volume parameters derived from the self-diffusion data are the same as those derived from deuterium NMR transverse relaxation-time measurements of the polymer in the same system. the equality of these two sets of experiments suggests a fundamental relationship between the two different processes. the simplest explanation is that the free volume necessary for the local segmental motion of the polymer and the translation of the solvent are similar