Dynamics of amorphous materials and dynamical heterogeneity

非晶材料动力学和动力学异质性

基本信息

批准号：
11640395
负责人：
FUKAO Koji
金额：
$ 2.18万
依托单位：
KYOTO UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

For two years we have investigated glass transitions and the dynamics of the α-process in polystyrene (PS), poly(vinyl acetate) (PVAc) and poly(methyl methacrylate) (PMMA) by dielectric relaxation spectroscopy and thermal expansion spectroscopy. The results obtained in our study are summarized as follows :PS : The profile of dielectric loss vs. frequency becomes broader as the film thickness decreases. This suggest that the depression of Tg is associated with the broadening of the relaxation times of the α-process. Relaxation measurements showed that the thickness dependence of the relaxation times of the α-process becomes much prominent near Tg compared with that at higher temperatures. This can be accounted for by assuming the existence of the characteristic length scale which increases as temperature approaches to Tg.PVAc : The temperature T_α at which the dielectric loss has a maximum due to the α-process in temperature domain at 100Hz has no molecular weight dependence in the Mw-range from 1.2×10^5 to 2.4×10^5. From this result, it is expected that Tg of thin PVAc films decreases with decreasing film thickness and the functional form of Tg with respect to thickness has almost no Mw-dependence.PMMA : The temperature T_α of the α-peak in the dielectric loss at 40Hz has been measured. It is found that the temperature T_α remains constant from the bulk thickness to a critical thickness d_c and below d_c it decreases rapidly with decreasing thickness. On the other hand, the temperature T_β of the β-process corresponding to T_α of the α-process decreases slightly with decreasing film thickness even for relatively larger thickness. Below the same critical thickness, T_β decreases rapidly with decreasing film thickness. The prominent thickness dependence of T_α and T_β has been discussed from the view point of confinement of polymer chains and cooperativity of the dynamics.

两年来，我们通过介电弛豫光谱和热膨胀光谱研究了聚苯乙烯 (PS)、聚醋酸乙烯酯 (PVAc) 和聚甲基丙烯酸甲酯 (PMMA) 的玻璃化转变和 α 过程动力学。我们的研究结果总结如下：PS：随着薄膜厚度的减小，介电损耗与频率的关系变得更宽，这表明 Tg 的降低与弛豫时间的加宽有关。 α 过程的弛豫时间的测量表明，与较高温度下相比，α 过程的弛豫时间的厚度依赖性变得更加突出，这可以通过假设存在增加的特征长度尺度来解释。当温度接近 Tg.PVAc 时：由于 100Hz 温域中的 α 过程，介电损耗达到最大值时的温度 T_α 在 Mw 范围内（从 1.2×10^5 到 1.2×10^5）没有分子量依赖性。 2.4×10^5 从该结果可以看出，PVAc 薄膜的 Tg 随着薄膜厚度的减小而降低，并且 Tg 相对于厚度的函数形式几乎不依赖于 Mw。PMMA：α- 的温度 T_α。测量了 40Hz 下介电损耗的峰值，发现温度 T_α 从体厚度到临界厚度 d_c 保持恒定，并且在 d_c 以下，温度 T_α 随着厚度的减小而迅速下降。另一方面，即使对于相对较大的厚度，与α过程的T_α相对应的β过程的温度T_β也随着膜厚度的减小而略有下降。在相同的临界厚度以下，T_β随着膜厚度的减小而迅速减小。从聚合物链的约束和动力学协同的角度讨论了T_α和T_β。