PHOTON-CORRELATION SPECTROSCOPY OF POLYSTYRENE IN THE GLASS-TRANSITION REGION

The dynamic characteristics of the light scattered by atactic polystyrene in the temperature range 92-110 °C are determined by digital photon correlation spectroscopy. Two discrete relaxation processes are present. A slow mode can be represented by an asymmetric Williams-Watts distribution of relaxation times and is essentially identical to that observed by Patterson et al. in the depolarized light-scattering spectrum. A fast process is well defined by a single exponential decay. The characteristic mean relaxation times are compared with the conventional relaxation map for polystyrene, as obtained by dynamic mechanical and dielectric techniques. Concordance between mechanical and photon correlation results in respect to the glass transition process is observed. While the activation energies are also identical with those derived from dielectric data, the characteristic frequencies are lower by two orders of magnitude. As for the α process, the derived activation energy of about 15 kcal/mol is in the range of general expectation, but lower by a factor of 2 than most of the mechanical information reported in the literature. Photon correlation techniques employing both the anisotropic and isotropic components appear to be powerful tools for dynamic relaxation spectroscopy in the glassy state. © 1979, American Chemical Society. All rights reserved.