Aging phenomena and non-equilibrium relaxation in polymer glass

1)通过电介质测量研究了不同老化过程下聚甲基丙烯酸甲酯（PMMA）薄膜的老化动力学。在许多情况下，在一定的时效温度下，介电常数随时效时间的增加而降低。在恒定速率模式下，包括在温度为Ta时的暂时停止，发现在Ta时的老化记忆被保留，然后在随后的加热过程中被召回。在负温循环过程中，在较大的温度变化后，观察到较强的回春效应。此外，还观察到温度变化的全记忆效应。这表明，当ΔT<-20 k时，T1下的老化与T2下的老化完全无关。2)通过测量复合电容，研究了无规聚苯乙烯薄膜的老化行为。在等温时效过程中，电容的实部随时效时间的延长而增大，虚部随时效时间的延长而减小。结果表明，实部和虚部的老化时间依赖关系主要与厚度和介电常数的变化有关。在薄膜中，厚度取决于老化的热历史，甚至在玻璃化转变之上。在薄膜中也观察到记忆和“返老还老”的效果。3)通过测量固定频率下的交流介电磁化率，研究了聚合物玻璃（聚甲基丙烯酸甲酯）在T1和T2两个温度之间温度变化ΔT （-20 K）后的老化行为。通过双温度（T-）位移测量，可以观察到随着ΔT的增加，从累积时效到非累积时效的交叉。基于激活动力学给出的动态相干长度的增长规律，我们得到了正t位移和负t位移的唯一相干长度。讨论了聚合物玻璃中温度混沌存在的可能性。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