Glass transitions and dynamics in thin polymer films: dielectric relaxation of thin films of polystyrene

Abstract

The glass transition temperature $T_{\mathrm{g}}$ and the temperature $T_{\alpha }$ corresponding to the peak in the dielectric loss due to the $\alpha$-process have been simultaneously determined as functions of film thickness d through dielectric measurements for polystyrene thin films supported on glass substrate. The dielectric loss peaks have also been investigated as functions of frequency for a given temperature. A decrease in $T_{\mathrm{g}}$ was observed with decreasing film thickness, while $T_{\alpha }$ was found to remain almost constant for $d>d_{\mathrm{c}}$ and to decrease drastically with decreasing d for $d<d_{\mathrm{c}}$. Here, $d_{\mathrm{c}}$ is a critical thickness dependent on molecular weight. The relaxation time of the $\alpha$-process was found to have a d dependence similar to that of $T_{\alpha }$. The relaxation function for the $\alpha$-process was obtained by using the observed frequency dependence of the peak profile of the dielectric loss. The exponent ${\beta }_{KWW}$, which was obtained from the relaxation functions, decreases as thickness decreases. This suggests that the distribution of relaxation times for the $\alpha$-process broadens with decreasing thickness. The thickness dependence of $T_{\mathrm{g}}$ is directly related to the distribution of relaxation times for the $\alpha$-process, not to the relaxation time itself.

13 pages, 11 figures, and 3 tables

References in corpus (3)

• Dynamics of Highly Supercooled Liquids:Heterogeneity, Rheology, and Diffusion
• Glass Transition Temperature and Dynamics of $\alpha$-Process in Thin Polymer Films
• Kinetic Heterogeneities in a Highly Supercooled Liquid

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