Relaxations in polystyrene below the glass transition studied by internal friction measurement

The results of internal friction (IF) measurement for polystyrene made over a wide frequency range of 0.001-10 Hz and in a temperature range of 11-74 °C were analyzed. At lower frequencies and higher temperatures, IF increases when the frequency is decreased, and the increase is larger for higher temperatures; IF increases when the temperature is increased, and the increase is larger for lower frequencies. These behaviors were explained by the viscosity relaxation based on the Maxwell model causing IF inversely proportional to frequency and viscosity. The relaxation time was experimentally determined as functions of temperature and frequency. The observed relaxation time could be represented as τ = τ0exp(E/kBT) (thermal activation); a combination of two relaxations was seen (double relaxation); τ0 and E were dependent on the frequency; log τ0 linearly decreased with increasing E (compensation effect). The relaxing elements were considered to jump cooperatively, and the element could be a part of molecular chains in the material. The results of the present study were compared with those obtained from our previous viscosity experiment.