Effects of electric field on thermodynamics and ordering of a dipolar liquid

We propose that an electric field's role in changing the structural disorder may be investigated by comparing the field-induced entropy decrease, Δ_ES, against the pressure-induced and cooling-induced entropy decreases, Δ_pS and Δ_TS, respectively, for the same increase in the dielectric α-relaxation time, Δτ_α, or in the viscosity. If these three quantities are found to be the same, the change in the number of microstates, Δln Ω = ΔS/R, would be the same whether there is an electric field-induced dipole vector alignment, or not. The available data [S. Samanta and R. Richert, J. Chem. Phys. 142, 044504 (2015)] show that Δ_ES ≅ Δ_pS, and Δ_ES ≅ Δ_TS. We further argue that in the case of conformational disorder without hydrodynamics, as for a flexible molecule's orientationally disordered or plastic crystal, Δ_TS would be more negative than Δ_ES for the same increase in Δτ_α. For cyclo-octanol plastic crystal, whose octyl-ring would lose some of its dielectrically inactive conformational degrees of freedom on cooling, Δ_TS is five-times Δ_ES. Hence the entropy of such crystals may not be related to their τ_α, an aspect relevant to certain biopolymer crystals. We also mention other effects of E. The findings are relevant to a number of recent studies on the analysis of the effect of electric field on a liquid's properties. The method can be used to study the role of other entropy-altering variables in liquid crystals and ferromagnetic liquids.