Aging phenomena and non-equilibrium relaxation in polymer glass

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1) The aging dynamics in thin films of poly (methyl methacrylate) (PMMA) have been investigated through dielectric measurements for different types of aging processes. The dielectric constant was found to decrease with increasing aging time at an aging temperature in many cases. In the constant-rate mode including a temporary stop at a temperature Ta, the memory of the aging at Ta was found to be kept and then to be recalled during the subsequent heating process. In the negative-temperature cycling process, a strong rejuvenation effect has been observed after a large temperature shift. Furthermore, a full memory effect has also been observed for the temperature shift. This suggests that the aging at T1 is totally independent of that at T2 for ΔT<-20 K.2) The aging behavior is investigated for thin films of atactic polystyrene through measurements of complex electric capacitance. During isothermal aging process the real part of the electric capacitance increases with aging time, while t … More he imaginary part decreases with aging time. This result suggests that the aging time dependence of the real and imaginary parts are mainly associated with change in thickness and dielectric permittivity, respectively. In thin films, the thickness depends on thermal history of aging even above the glass transition. Memory and 'rejuvenation' effects are also observed in the thin films.3) The aging behavior of polymer glass, poly(methyl methacrylate), has been investigated through the measurement of ac dielectric susceptibility at a fixed frequency after a temperature shift ΔT (-20 K) between two temperatures, T1 and T2. A crossover from cumulative aging to non-cumulative aging could be observed with increasing ΔT using a twin temperature (T-) shift measurement. Based on a growth law of a dynamical coherent length given by activated dynamics, we obtained a unique coherent length for positive and negative T-shifts. The possibility of the existence of temperature chaos in polymer glasses is discussed. Less