Influence of thermal orientation on the dielectric properties of dendronised poly(2-oxazoline) hybrid membranes

Abstract

Dendronised poly(2-oxazoline) hybrid membranes were prepared by solution impregnation and phase inversion precipitation. Dielectric Thermal Analysis (DETA) was used to investigate the effect of the annealing temperature on the dielectric properties of these Side-Chain Liquid-Crystalline Polymers (SCLCPs). Independent of the different thermal treatments, the poly(2-oxazoline) hybrid membranes show similar dielectric spectra containing the same four relaxation mechanisms (γ-, α_Tg-, α_Clear-, and ρ-relaxation). The thermal orientation reduces the activation energy of the γ-relaxation, by modifying the steric hindrance of the associated aliphatic side chains. Aligning the polymer chains to each other, due to thermal annealing, leads to a less fragile structure. This reduced cooperativity decreases the temperature of the α_Tg-relaxation, related to the glass transition. The highly ordered structure of the oriented membranes increases the activation energy and temperature of the α_Clear-relaxation, associated with the freeing movement of the mesogenic side groups, especially in the homeotropically aligned membrane. The random orientation decreases the electron conductivity and its thermal activation, while the homeotropic alignment results in an increase, due to the orientation of the columns. The thermal orientation of SCLCPs leads to differences in the temperature dependence and cooperativity of the molecular relaxations and the conductive properties, providing valuable insights into their molecular structure and arrangement.