基于Weiss分子场理论对极性液体中静态介电常数随温度变化及其相应取向关联的研究

迄今为止,并没有被普遍接受的液体静态介电常数的微观理论模型, 主要原因是对属于强关联系统的液体中分子之间的取向关联特征仍不十分清楚. 本文基于Weiss分子场理论(WMFT), 对水(water, H₂O)、甲醇(methanol, CH₄O)、乙醇(ethanol, C₂H₆O)和正丙醇(1-propanol, C₃H₈O)等4种极性液体中静态介电常数, 具体为Curie-Weiss常数、Curie温度和Weiss分子场因子随温度变化规律进行分析研究, 得出上述液体中: 1)铁电关联(ferroelectric correlation, FC)和反铁电关联(anti-ferroelectric correlation, AFC)共存, 且FC比AFC强得多, 以及随温度降低FC减弱和/或AFC增强; 2)结构均匀的WMFT不能定量描述上述液体中足够低的温度下反常大的静态介电常数. 可以想象FC和较弱AFC的共存必然导致极性液体中关联序的空间不均匀, 由此作者提出了空间不均匀关联序的粗粒近似的Weiss分子场理论, 并用此理论对上述液体中静态介电常数随温度快速变化的行为进行了解释. 上述结果对深入认知液体物理学, 包括玻璃化转变机制的探索, 无疑是有价值的.

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

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 ε_s 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.