Research Reactor Institute, Kyoto University, Kumatori, Sennan-gun, Osaka 590-0494, Japan.
J-PARC, Material and Life Science Division, Institute of Material Structure Science, High Energy Accelerator Research Organization (KEK), 203-1 Shirakata, Tokai-mura, Naka-gun, Ibaraki, 319-1106, Japan.
Phys Rev E. 2018 Jan;97(1-1):012501. doi: 10.1103/PhysRevE.97.012501.
In this study, we investigate the α process of a polystyrene thin film using inelastic neutron scattering (INS), dielectric relaxation spectroscopy (DRS), and thermal expansion spectroscopy (TES). The DRS and TES measurements exhibited a decrease in glass transition temperature (T_{g}) with film thickness. On the other hand, an increase in T_{g} was observed in INS studies. In order to interpret this contradiction, we investigated the temperature dependence of the peak frequency (f_{m}) of the α process probed by DRS and TES. The experiments revealed an increase in the peak frequency (f_{m}) with decreasing film thickness in the frequency region. This observation is consistent with the observed decrease in T_{g} with thickness. Interestingly, the increase in T_{g} with film thickness was confirmed by fitting the temperature dependence measurements of the peak frequency with the Vogel-Fulcher-Tammann equation, within the frequency region probed by INS. The discrepancy between INS and DRS or TES descriptions of the α process is likely to be attributed to a decrease in the apparent activation energy with film thickness and reduced mobility, due to the impenetrable wall effect.
在这项研究中，我们使用非弹性中子散射（INS）、介电弛豫谱（DRS）和热膨胀谱（TES）研究了聚苯乙烯薄膜的α过程。DRS 和 TES 测量表明玻璃化转变温度（T_g）随薄膜厚度的降低而降低。另一方面，INS 研究中观察到 T_g 的增加。为了解释这种矛盾，我们研究了 DRS 和 TES 探测的α过程的峰值频率（f_m）随温度的变化。实验表明，在频率区域内，随着薄膜厚度的减小，峰值频率（f_m）增加。这一观察结果与 T_g 随厚度减小的趋势一致。有趣的是，通过将峰值频率的温度依赖性测量与 Vogel-Fulcher-Tammann 方程拟合，在 INS 探测的频率范围内，证实了 T_g 随薄膜厚度的增加而增加。INS 和 DRS 或 TES 对α过程的描述之间的差异可能归因于由于不可渗透的壁效应导致的表观活化能随薄膜厚度的降低和迁移率的降低。
