Low-Frequency Chain Dynamics of Poly(n-hexyl methacrylate) by Dielectric Spectroscopies

Abstract

The study of poly(n-hexyl methacrylate) has been performed by both thermo-stimulated currents (TSC) and dynamic dielectric spectroscopy (DDS) in order to better define the nature of molecular mobility in the glass transition temperature range. TSC results reveal the existence of three dipolar relaxation modes: α, ascribed to the glass relaxation; β, assigned to a secondary relaxation mode; and α‘, associated with the dielectric manifestation of the liquid−liquid transition. DDS allowed us to follow the merging of the α and β modes as frequency increases from 10-2 to 106 Hz. Then the fractional polarizations protocol permitted us to define at low frequency (10-3−10-2 Hz) the fine structure of these complex relaxations: relaxation times isolated for the β and α modes are widely distributed and obey an Arrhenius law while those isolated for the α‘ mode are narrowly distributed and are better defined by a Vogel−Tamman−Fulcher law. Finally, the evolution of the activation enthalpy helps us to precise the nature of involved molecular movements.