Aging phenomena in poly(methyl methacrylate) thin films: memory and rejuvenation effects.
Aging phenomena in poly(methyl methacrylate) thin films: memory and rejuvenation effects.
复制标题
DOI：
10.1103/physreve.71.041803
复制
发表时间：
2004-10
期刊：
影响因子：
--
通讯作者：
K. Fukao;A. Sakamoto
中科院分区：
文献类型：
--
作者：
K. Fukao;A. Sakamoto
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。对于厚度小于26 nm的薄膜，在玻璃化转变温度附近的长时间区域（>或=11 h）中也观察到介电常数的增加。在包括在温度T（a）处暂时停止的恒定速率模式中，发现在T（a）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，当Δ T约为-20 K时，在从初始温度T1到第二温度T2（= T1 + Δ T）的温度变化之后，观察到强烈的复原效应。此外，对于从T2到T1的温度偏移，也观察到完全记忆效应。这表明，在Δ T约为-20 K时，T1处的老化与T2处的老化完全无关。随着Δ T/的减小，发现两个温度之间的老化的独立性减弱，即，有效时间是T1处的老化对T2处的老化的贡献的量度，在Δ T的负区域中，有效时间是/Δ T/的递减函数。随着膜厚度从514 nm减小到26 nm，发现有效时间的/Δ T/依赖性变得更强。在T2的老化的贡献，在T1消失更迅速地增加/Δ T/在薄膜的几何形状比在体状态。
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. An increase in the dielectric constant was also observed in the long-time region (>or=11 h) near the glass transition temperature for thin films with thickness less than 26 nm . In the constant-rate mode including a temporary stop at a temperature T(a) , the memory of the aging at T(a) 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 temperature shift from the initial temperature T1 to the second temperature T2 (= T1 +DeltaT) when DeltaT approximately -20 K . Furthermore, a full memory effect has also been observed for the temperature shift from T2 to T1 . This suggests that the aging at T1 is totally independent of that at T2 for DeltaT approximately -20 K. As /DeltaT/ decreases, the independence of the aging between the two temperatures was found to be weakened-i.e., the effective time, which is a measure of the contribution of the aging at T1 to that at T2 , is a decreasing function of /DeltaT/ in the negative region of DeltaT . As the film thickness decreases from 514 nm to 26 nm, the /DeltaT/ dependence of the effective time was found to become much stronger. The contribution of the aging at T2 to that at T1 disappears more rapidly with increasing /DeltaT/ in thin-film geometry than in the bulk state.