Dielectric relaxation in antiplasticized poly n-butyl methacrylate system

Abstract

The dielectric αβrelaxation process has been studied for poly n-butyl methacrylate (PBMA) in presence of various additives such as cholesteric liquid crystals and some isotropic liquids. Addition of isotropic liquids increased log ( f max) with increasing concentration at constant temperature and decreased the activation energy. The cholesteric liquid crystal additives, however, decreased log ( f max) and the free volume with increasing concentration at constant temperature. The data gathered were fitted to a master curve to evaluate the decay function, ф(t) and the parameterβ. The normalized loss curves were found to be broadened with increased asymmetry both with isotropic and cholesteric liquid crystal additives. These studies clearly revealed the antiplasticization effect of some of the cholesteryl liquid crystal additives. The extent of broadening and the asymmetry of the loss curves cannot be explained on the basis of free volume theory alone and a mechanistic approach is used to explain the results. The values of Δβ Δc have thus been explained on the basis of a gradient of the segments mobility leading to an increased spread of relaxation times.