Light scattering studies on long‐range density fluctuations in a glass‐forming polymer

Abstract

Abstract Static and dynamic light scattering measurements were performed on a glass‐forming polymer, poly(methyl‐ p ‐tolylsiloxane) (PMpTS; T g =−17°C), in a temperature range of 30°C to 120°C. It was found that long‐range density fluctuations, so‐called clusters, are observed in this polymer. They are characterized by “excess” angular‐dependent isotropic scattered intensity and additional slow decay in the photon correlation function. These properties are generally observed in low molecular weight glass formers as well as in glass‐forming polymers. In addition, we found that the clusters completely disappear above about 90°C. The kinetics of the cluster growth was also studied by temperature jump experiments. During the cluster formation process after the temperature jump, we measured the angular‐dependent polarized scattered intensities, and the photon correlation function as a function of annealing time. We discuss the cluster growth kinetics based on these results, especially the time evolution of the correlation length ξ OZ evaluated using the Ornstein‐Zernike formula, the isotropic scattering intensity I OZ (0) at q =0, and the correlation time τ cl of the cluster decay. Finally, we briefly discuss some properties of the equilibrated clusters, which are well reproducible.