On investigation of aggregation of molecular dipoles in liquids

The paper is related to the methods of detection of dipolar self-association in molecular liquids and identification of the intermolecular entities formed. At present, this basic problem of molecular physics of liquid state cannot be investigated in a simple and, what is the most important, unambiguous way. The method used currently consists in determination of the Kirkwood correlation factor, which value is often totally uncertain because of the uncertainties in determination of the high-frequency permittivity of studied liquids. That problem causes an appearance of numerous papers containing quite different and often even contradictory results. Here we analyze the method that does not require an ungrateful effort in the determination of some parameters. Instead, it requires the precise measurements of the static permittivity of liquids in possible wide temperature range. The method is based on the temperature derivative of the static permittivity of studied liquid. This derivative, according to the theory of Frohlich, is proportional to the orientational entropy increment induced by the probing electric field. The method is then sensitive to the polarity of the liquid and successfully reveals a type of the dipolar self-association occurring in studied liquid. Unquestionable advantages of this method are illustrated on the examples of two groups of dipolar liquids: these containing the oxygen in their structure (including the water) and those containing the cyano group -C equivalent to N. (C) 2016 Elsevier B.V. All rights reserved.