Photon correlation spectroscopy of atactic polystyrene in the bulk state near Tg

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Abstract
The dynamic characteristics of light scattered by atactic polystyrene in the glass transition region have been determined by photon correlation spectroscopy. The results are interpreted based on the assumption that the relaxation function can be represented by: ⊘(t) = α exp {-(t/τ)β} We find that above Tg, the correlation function exhibits two relaxation modes: one corresponds to the α-relaxation process with a wide distribution of relaxation times; the other may be the β process with a single exponential decay. The average relaxation times for each process are two orders of magnitude slower than those which characterize the frequency-dependent modulus in conventional mechanical relaxation experiments. This stems from the fact that the light scattering experiment is equivalent to the measurement of a time-dependent volume creep compliance rather than a dynamic modulus.