Dynamics of glass-forming liquids. XII. Dielectric study of primary and secondary relaxations in ethylcyclohexane

The dynamics of ethylcyclohexane are investigated by high resolution dielectric spectroscopy aiming to characterize the relevant relaxational features of this simple system in its fluid, supercooled liquid, and glassy states. The dielectric signature of structural relaxation is a primary loss peak with amplitude Δε = 0.01, and a secondary loss process is found in the glassy state. This β relaxation is compared with a “slow” process revealed by ultrasonics and with previously found γ and χ processes in similar materials containing the cyclohexyl group. The results suggest that this secondary process is an intramolecular mode rather than a Johari–Goldstein process, consistent with its persistence in the liquid state at slow relaxation times which exceed those of the α process. The dielectric activity of such a slow process requires that the dipole magnitude changes with the intramolecular transition, whereas a change in dipole direction only would be masked by the faster structural relaxation.