Cooperative Dynamics in Polystyrene and Low-Mass Molecule Mixtures

Abstract

We conducted dielectric and viscoelastic relaxation measurements for polystyrene (PS)/4-pentyl-4′-cyanobiphenyl (5CB) and PS/4-pentyl-4′′-cyanoterphenyl (5CT) mixtures in the miscible state with the weight fractions of 5CB or 5CT from 0.04 to 0.27 to examine the relationship between two-component dynamics in the mixture. Dielectric relaxation measurements mainly probed the dynamics of low-mass molecule (LM), 5CB or 5CT, because of the much larger dipole moment of LMs compared to that of PS. PS/5CB mixtures exhibited bimodal dielectric relaxation, while PS/5CT showed unimodal relaxation. The observed two relaxation modes (slow and fast modes) in PS/5CB were attributed to the full rotational motion and partial rotational motion of 5CB, respectively. The latter motion is allowed in the restricted space surrounded by less mobile PS matrix. In the case of 5CT, the fast mode was suppressed due to the larger size of 5CT molecule, and only the slow mode (rotational mode) appeared. The relaxation times of slow mod...