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

点击翻译按钮获取中文摘要

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.