Toward A Better Understanding Of Dielectric Responses Of Van Der Waals Liquids: The Role Of Chemical Structures

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 alpha-relaxation and the dielectric strength Delta epsilon, 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-vinyl1,3-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 alpha-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 alpha-relaxation frequency dispersion for the three glass-formers but also the excess wing which is the unresolved Johari-Goldstein beta-relaxation. On the other hand, the other thermodynamics related parameters of the alpha-relaxation dynamics, including the glass transition temperature T-g, the fragility index m(P), and activation volume Delta V-act, are not uniformly the same for all three glass-formers. Published by AIP Publishing.