Laser light scattering as a probe for structure and dynamics in bulk polymers: Polystyrene

Abstract

We begin with an outline of a theory of density fluctuations in the glassy state based on a partial freeze-in of an ordering parameter, as derived from previous equation of state investigations. Then laser light scattering studies of glasses formed by atactic polystyrene are described. Photon correlation analysis indicates two relaxation mechanisms. A slow process dominates aboveT g , has a wide asymmetric distribution of relaxation times and is evidently related to the glass transition phenomenon. A small-amplitude fast decay with a narrow relaxation spectrum is also observed. BelowT g , this mode is shown to be dependent on scattering angle and is evidently a diffusion mechanism, which may be related to theβ-relaxation process. Relative integrated intensities are presented for isotropic and depolarized scattering from glasses densified by pressurization in the melt, followed by isobaric cooling to 25°C and depressurization. The depolarized scattering for the glass formed at atmospheric pressure has a value consistent with a completely disordered glass. However, a small increase in depolarized scattering appears to occur on densification. This result may reflect a small increase in intersegmental ordering in glassy polystyrene upon densification. The isotropic scattering shows a large systematic increase in the densified glass. This is apparently the result of an inhomogeneous density change during the depressurization step.