Scaling the dynamics of orientationally disordered mixed crystals

Abstract

The evolution of the primary relaxation time of orientationally disordered (OD) mixed crystals [(CH3)2C(CH2OH)2]1−X[(CH3)C(CH2OH)3]X, with 0<X ≤ 0.5, on approaching the glass temperature (Tg) is discussed. The application of the distortion-sensitive, derivative-based procedure revealed a limited adequacy of the Vogel–Fulcher–Tammann parametrization and a superiority of the critical-like description τ∝(T−TC)−ϕ′, ϕ′=9–11.5, and TC ∼ Tg−10 K. Basing on these results as well as that of Drozd-Rzoska et al. [J. Chem. Phys. 129, 184509 (2008)] the question arises whether such behavior may be suggested as the optimal universal pattern for dynamics in vitrifying OD crystals (plastic crystals). The obtained behavior is in fair agreement with the dynamic scaling model(DSM)[R. H. Colby, Phys. Rev. E 61, 1783(2000)], originally proposed for vitrifying molecular liquids and polymers. The application of DSM made it possible to estimate the size of the cooperatively rearranging regions (“heterogeneities”) in OD phases near Tg.