Correlating the Segmental Relaxation Time of Polystyrene

A previous related paper dealing with the density relaxation of polystyrene (PS) has shown that the equilibrium relaxation time (τ ) has a purely exponential temperature dependence (ETD) below ≈100 °C. Such an ETD is now also confirmed based upon available dielectric spectra data for PS. By combining the ETD behavior of τ (or a ) at low temperatures with a VFTH behavior at higher temperatures (based mainly on available recoverable shear compliance data), a composite correlation for τ (or a ) is developed, which is continuous with continuous slope at a crossover temperature that is found to be 99.22 °C, where τ = 92.15 s. This composite representation is shown to describe (without any adjustable parameters) available independent data for the segmental relaxation time over a finite range both above and below T (i.e., the glass transition temperature).