Effect of high field on dielectric relaxation properties of polycarbonate

It is known that glassy state is a non-equilibrium state. Due to the energy excess, resulting from kinetic conditions during cooling from the liquid state, all glasses and especially polymers sustain a phenomenon called physical ageing or structural relaxation under the glass transition temperature. This phenomenon results in decrease with time of physical properties due to rearrangements of macromolecules in order to decrease their energy. This decrease directly affects the durability of polymers and molecules movements are associated with glass transition dynamics. But, the interaction between macromolecules movements induced by physical ageing and by electrical field is not known. In order to clarify this interaction, a model thermoplastic, polycarbonate, has been studied with dielectric spectroscopy under different high-field AC conditions up to 700V/mm. Dielectric spectroscopy technique has been chosen because it allows simultaneously to apply an electrical field and to follow the molecular dynamics by controlling the temperature.