Toward a better understanding of dielectric responses of van der Waals liquids: The role of chemical structures

Abstract

Exhaustive analysis of dielectric relaxation data of van der Waals glass-forming liquids revealed a strong correlation between the width of the frequency dispersion of the α-relaxation and the dielectric strength Δε, originating from the dipole-dipole interaction contribution to the intermolecular potential [M. Paluch et al., Phys. Rev. Lett. 116, 025702 (2016)]. The two van der Waals liquids, 4-vinyl-1,3-dioxolan-2-one (VPC) and 4-ethyl-1,3-dioxolan-2-one (EPC), have chemical structures modified from that of propylene carbonate. All three glass-formers have very similar values of dipole moments, exactly the same dielectric strength, and hence identical frequency dispersion of the α-relaxation in all three glass-formers is expected if the correlation holds. Based on this expectation, we performed dielectric relaxation measurements of the VPC and EPC at ambient and elevated pressures. The results obtained show not only identical α-relaxation frequency dispersion for the three glass-formers but also the excess wing which is the unresolved Johari-Goldstein β-relaxation. On the other hand, the other thermodynamics related parameters of the α-relaxation dynamics, including the glass transition temperature Tg, the fragility index mP, and activation volume ΔVact, are not uniformly the same for all three glass-formers.