Temperature dependence of vibrational motions of thin polystyrene films by infrared reflection-absorption spectroscopy: A single measurement tool for monitoring of glass transition and temperature history

Abstract

A method for monitoring of vibrational response and temperature region of glass transition by a single analysis is introduced with the use of an otherwise well-known spectroscopic method. The temperature-dependent changes of polystyrene (PS) thin films were investigated by polarization-modulated infrared reflection-absorption spectroscopy. The study revealed that changes in individual spectral regions with the temperature increase are specific and provide the relation to the processing and thermal history of the thin film. Temperature responses of infrared spectral region areas; an abrupt change of Car-H stretching, a step-like change of Car-H out-of-plane bending, a linear decrease of C–H stretching and C–H bending area, granted information on the temperature domain represented by local molecular motion change (β-transition) of PS. The different behavior of spectral regions is rationalized by consideration of vibrational free volume contribution to the total free volume of the system that is certainly influenced by functional groups nature, such as their size, geometry and involvement of non-bonding interaction.