Effect of pressure on molecular dynamics of spin probes in polyethylene

Abstract

A study was made of the effect of pressure on rotary and translational mobility of spin probes (stable nitroxyl radicals) in PE. Activation energy values were determined at constant pressure and with constant polymer volume, and activation volumes of rotation and translation were established. It was shown that the translational mobility of spin probes is mainly determined by the energy of formation of the fluctuation gap. For the rotary mobility the energy of formation of the fluctuation hole is also of major significance, however, the activation energy of reorientation should also be considered (with a hole of requisite volume), which may reach ∼30% of the overall energy of activation. The elementary processes of translational movement requires greater activation volume than the elementary stage of rotation. With an increase in the size of spin probe, differences in activation volumes of rotation and translation decrease, therefore for large particles these motions show a correlation, they take place at similar frequencies, while for small particles-largely independently.