GLASS TRANSITIONS IN CONFINED GEOMETRY AND DYNAMICAL CROSSOVER OF POLYMER CHAIN DYNAMICS

1)用介电弛豫谱研究了顺式-1，4-聚异戊二烯(PIP)薄膜的动力学行为。在PIP薄膜中，可以观察到α过程和简正模式的动力学。α过程与玻璃化转变有关，正常模式是整个聚合物链的运动(旋转动力学)。目前的测量表明，随着薄膜厚度的减小，α过程的动力学几乎保持不变。另一方面，正常模式的动力学通过共存状态转变为另一种更快的动力学。这一结果表明，在薄膜内部存在一些聚合物的有效链长小于原始链长的区域，并且这些区域对介电弛豫谱所观察到的弛豫动力学的贡献随着薄膜厚度的减小而变得更加显著。在聚甲基丙烯酸甲酯(PMMA)薄膜中，可以观察到α过程动力学的规则性依赖，而不能观察到β过程的规则性依赖。此外，随着薄膜厚度的减小，α-过程的规则性依赖性变弱。3)研究了PMMA玻璃态在玻璃化转变温度下的老化动力学。可以观察到令人惊讶的记忆和恢复活力的效果。这表明，不仅聚合物玻璃，而且自旋玻璃的老化动力学都存在普遍的物理规律。为了理解玻璃化转变的机制，必须阐明这种普遍行为。为此，在JSPS Kakeni的支持下，一个新的项目刚刚开始。

1) The dynamics of thin films of cis-1, 4-polyisoprene (PIP) has been investigated by using dielectric relaxation spectroscopy. In thin films of PIP, dynamics of alpha-process and normal mode can be observed. The alpha-process is related to glass transitions and the normal mode is the motion of entire polymer chains (reptation dynamics). The present measurements show that the dynamics of the alpha-process remains almost unchanged with decreasing film thickness. On the other hand, the dynamics of the normal mode changes into another faster dynamics via a coexistent state. This result implies that within the films there are some regions where the effective chain length of polymers is shorter that the original chain length, and that the contributions of such regions to relaxation dynamics observed by dielectric relaxation spectroscopy become more significant with decreasing film thickness. As a result, the crossover of dynamics from the normal mode to another faster mode could be observed.2) In thin films of poly (methyl methacrylate) (PMMA), we could observe the tacticity dependence of the dynamics of alpha-process, while no tacticity dependence of the beta-process could be observed. Furthermore, the tacticity dependence of alpha-process becomes weaker with decreasing film thickness. This result suggests that there is a competition between the length scale of tacticity order and the characteristic length of the alpha-process.3) The aging dynamics below the glass transition temperature has been investigated for the glassy states of PMMA. Surprising memory and rejuvenation effects could be observed. This suggests that there is a universal physical law of aging dynamics not only for polymer glasses but also for spin glasses. The universal behavior should be elucidated in order to understand the mechanism of glass transitions. For this purpose, a new project has just started under the support from JSPS Kakenhi.