Study on the variation of static dielectric constant with temperature and the corresponding orientational correlation in polar liquids by using Weiss's molecular field theory

Abstract

There is no widely accepted microscopic theoretical model of the static dielectric constant of liquids so far. This is mainly because the orientational correlation between molecules in liquids, belonging to the strong correlation systems, is still not clear. In this paper, the variations of the static dielectric constants of 4 kinds of polar liquids, i.e., water, methanol, ethanol and 1-propanol, specifically the Curie-Weiss constant, Curie temperature and Weiss molecular field factor with temperature are studied according to the Weiss's molecular field theory (WMFT), and it is concluded that 1) ferroelectric correlations (FCs) and anti-ferroelectric correlations (AFCs) between molecules coexist in the liquids, and FC is stronger than AFC, as well as FC becomes weak and/or AFC stronger with temperature decreasing; 2) WMFT of homogeneous structure cannot quantitatively describe the abnormally large values of εs of the liquids at low enough T. It can be expected that the coexistence of FC and weak AFC must lead to the spatial distribution of the correlation orders, and consequently, we propose an WMFT of coarse grain approximation of the spatial distribution correlation orders, and use the WMFT to explain why the static dielectric constant varies rapidly with temperature. The above results can benefit the understanding of the liquid physics, including the glass transition mechanism.