DENSITY AND CONCENTRATION FLUCTUATIONS IN PLASTICIZED POLY(CYCLOHEXYL METHACRYLATE)

Polarized photon-correlation functions of high molecular weight plasticized PCHMA samples have been studied in the temperature range from near Tg to Tg + 150 K. The time-correlation function can measure both the density fluctuations caused by primary segmental relaxation and concentration fluctuations due to cooperative diffusion. It is the first time in a dynamic light-scattering experiment that both concentration and density correlation functions have been observed within the time window of the technique at the same temperature for a range of temperatures. The average primary relaxation times exhibit a strong temperature dependence with activation parameters experimentally the same for all plasticizer (DOP) concentrations. On the contrary, the activation parameters for the slow relaxation process were found to decrease with increasing DOP concentration. The coupling model, which is applicable to both segmental relaxation and cooperative diffusion, can explain this difference together with all accessorial features of the present experimental data. © 1990, American Chemical Society. All rights reserved.