ABSTRACT

At high temperatures, polymeric material is in the liquid state. When the material is cooled down from a high temperature to a lower temperature at an appropriate cooling rate, it assumes a glassy state at the glass transition temperature, Tg [1]. For polymeric systems, the α-process, known as cooperative segmental motion, becomes slower with decreasing temperature [2]. The characteristic time of the α-process changes from a microscopic time scale to a macroscopic one during a temperature change of only several tens of degrees. At Tg, this characteristic time is equal to 102-103 s; hence, the segmental motion is almost frozen below Tg. As the mechanism of the glass transition is not yet fully understood, understanding it is one of the most important unsolved problems in condensed matter physics [3]. Dynamical heterogeneity is the most important concept for understanding the glass transition [4,5]. Many experiments and simulations have shown its

7.1 Introduction 243

7.2 Glass transition and dynamics in thin polymer films investigated by DRS 244

7.2.1 Dielectric relaxation spectroscopy and capacitive dilatometry 245

7.2.2 Glass transition in PS thin films 246

7.2.3 Thermal expansion spectroscopy 247

7.2.4 Recent developments in glass transition in PS thin films 249

7.3 Aging dynamics in thin films of polymer glasses 250

7.3.1 Kovacs effects 250

7.3.2 Memory and rejuvenation effects 252

7.3.3 Aging in dielectric permittivity and volume 255

7.3.4 Confinement effect of aging in polymer glass 256

7.4 Glass transition dynamics of stacked thin polymer films 256

7.4.1 Thermal properties 257

7.4.2 Dielectric properties 257

7.4.3 Tg and the relaxation rate of the α-process 260 7.5 Summary 262

Acknowledgments 262

References 263

existence [6-8]. That is, molecular motion related to the glass transition has shown cooperative behavior with respect to spatial correlation in dynamics [9]. Thus, the existence of dynamical heterogeneity may be directly related to the characteristic length scale, which governs the mechanism of the glass transition.