Aging phenomena and non-equilibrium relaxation in polymer glass

1)通过介电测量研究了聚甲基丙烯酸甲酯（PMMA）薄膜在不同类型老化过程中的老化动力学。在许多情况下，在老化温度下，介电常数随着老化时间的增加而降低。在包括在温度Ta处暂时停止的恒定速率模式中，发现Ta处的老化的记忆被保持，然后在随后的加热过程中被调用。在负温循环过程中，在大的温度漂移后观察到强烈的再生效应。此外，还观察到温度漂移的完全记忆效应。这表明，当ΔT<-20 K时，T1的老化与T2的老化完全无关。2）通过测量复电容，研究了无规聚苯乙烯薄膜的老化行为。在等温时效过程中，电容的真实的部分随时效时间的延长而增加，而在等温时效过程中，电容的真实部分随时效时间的延长而增加， ...更多信息 虚部随老化时间的延长而减小。这一结果表明，老化时间依赖性的真实的和虚部主要与厚度和介电常数的变化，分别。在薄膜中，厚度取决于老化的热历史，甚至高于玻璃化转变。在薄膜中还观察到记忆和“复原”效应。3）通过在两个温度T1和T2之间的温度偏移ΔT（-20 K）后在固定频率下测量交流介电磁化率来研究聚合物玻璃（聚甲基丙烯酸甲酯）的老化行为。使用双温度（T-）偏移测量，随着ΔT的增加，可以观察到从累积老化到非累积老化的交叉。基于激活动力学给出的动力学相干长度的增长规律，我们得到了正、负T位移的唯一相干长度。讨论了聚合物玻璃中存在温度混沌的可能性。少

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