Photon Correlation Spectroscopy of Amorphous Polymers Near tg Region.

Homodyne photon correlation spectroscopy measurements of poly(vinyl acetate) and poly(di-n-butyl itaconate) and depolarized photon correlation spectroscopy measurements of polystyrene near the glass transition temperature have been carried out. The light scattering (photon correlation) results are compared with mechanical and dielectric relaxation data. For poly(vinyl acetate) and polystyrene, the photon correlation functions are well described by a single Kohlrausch -Williams-Watts (KWW) function. The distribution parameter, beta, is around 0.34 ~ 0.38 which is consistent with the literature results of the glass transition process. The photon correlation function of PDBI can be described either by a single KWW function or by a double KWW function. The distribution parameter, beta, of single KWW function fit to photon correlation spectroscopy data of PDBI is around ~0.24 which indicates a much wider distribution of relaxation times than those observed for the glass transition process in polyvinylacetate and polystyrene suggesting that a second relaxation process present in addition to the alpha(glass transition) relaxation process. Analysis of the correlation functions of PDBI by fitting to the sum of two K-W-W functions suggests that there is a coupling between the side-chain and backbone motions. The predicted theoretical relationship between the compressional (or bulk) compliance and the dynamic light scattering correlation function arising from density fluctuations has been evaluated. Good agreement between the dynamic light scattering results and bulk compliance relaxation data of PVAC is found. The depolarized photon correlation function of polystyrene was also compared with the shear stress relaxation modulus. The relaxation behaviour of the depolarized photon correlation spectrum is very similar to that of the transition zone of the shear stress relaxation modulus.