COMPONENT DYNAMICS IN POLYSTYRENE BIS(2-ETHYLHEXYL) PHTHALATE SOLUTIONS BY POLARIZED AND DEPOLARIZED LIGHT-SCATTERING AND DIELECTRIC-SPECTROSCOPY

Depolarized Rayleigh, polarized Rayleigh-Brillouin scattering, and die lectric spectroscopy have been used to resolve the dynamics of the two components in concentrated solutions of polystyrene (PS) in bis(2-eth ylhexyl)phthalate (DOP) close to and above the glass transition temper ature. Two distinct time scales of motion exist in the macroscopically homogeneous PS/DOP solutions which are associated with the faster sol vent (DOP) and slower polymer (PS) dynamics with different temperature shift factors. The width and the degree of asymmetry of the distribut ion of relaxation times determined as a function of temperature for bo th components increase as temperature decreases, and also as the PS co ncentration increases, indicating that the contribution at a lower fre quency has a larger temperature shift factor, alpha(T). The temperatur e dependencies of the most probable relaxation times, tau(iota) with i ota = 1, 2, of both processes conform to the Vogel-Fulcher-Tammann (VF T) equation. These VFT dependencies for the two components, iota = 1, 2, in the mixture when replotted respectively against T-g iota/T, wher e T-g iota is the temperature at which tau(iota)(T-g iota) = 10(o) s, show a trend that can be expected from the enhancement (mitigation) of constraint dynamics of DOP (PS) with further addition of PS (DOP) to the mixture. There is an exact analogy between the current experimenta l findings in the mixture of polymer and small-molecule diluent and wh at we have found in the component dynamics in binary miscible polymer blends. Thus the physics in these two systems are similar. The Rayleig h-Brillouin experiment revealed the existence of an additional faster process associated with a localized motion of the phenyl group of the DOP molecule in the concentrated solutions in agreement with a previou sly reported study.