Temperature Dependence of the Activation Volume of Secondary Relaxation in Glass Formers

We study a nonmonotonic behavior with temperature of the activation volume ΔVβ of secondary relaxation in PPGE [Poly[(phenyl glycidyl ether)-co-formaldehyde]] and PVAc [Poly(vinyl acetate)] glass formers. Our results show that the non-monotonic behaviour of secondary relaxation does not depend on the type of the secondary relaxation. Moreover, the study of secondary relaxation under pressure at isothermal paths shows two different behaviours of ΔVβ in the glassy state (which describe two different types of glasses); for temperatures higher than the glass transition temperature (Tg), ΔVβ increases with a decrease of the temperature while at temperatures lower than Tg, ΔVβ decreases with a decrease of the temperature.