Dynamic crossover and the Debye–Stokes–Einstein relation in liquid N,N-diethyl-3-methylbenzamide (DEET)

Abstract

The dynamic glass transition in the molecular liquid DEET is investigated in wide temperature and pressure ranges using depolarized dynamic light scattering (DDLS), broadband dielectric spectroscopy (BDS), calorimetry, and rheology. It is found that the viscosity and structural α relaxation rates all exhibit an identical type of thermal activation in the measured temperature and pressure ranges. In addition, it is shown that these characteristic quantities exhibit a dynamic crossover at 240 ± 5 K at ambient pressure. Contrary to recent assertions in the literature, it is demonstrated that the dynamic crossover by no means generally implies a violation of the Debye–Stokes–Einstein relation in molecular glass forming liquids.