DIELECTRIC-CONSTANT AND DENSITY VARIATIONS IN PURE LIQUIDS - THEORETICAL RELATIONS, COMPARISON WITH EXPERIMENT

Theoretical expressions of the density fluctuation of the dielectric c onstant (depsilon/dd)P or DFDC have been deduced from Clausius-Mossott i, Onsager relations and from a more general expression of the molecul ar polarization. The dielectric constant at each point of the liquid h as been considered as a function of the number N of molecules per volu me unit, of the temperature T and of the pressure P. In the general ca se the calculation of DFDC leads to three terms : an isothermal one (p artial derivative epsilon/partial derivative d)P,T and two others from (partial derivative epsilon/partial derivative T)P,N/(dd/dT)P. By tes ting a hundred and eighteen organic solvents the results have been com pared to the experimental values deduced from (depsilon/dT)P and (dd/d T)P measurements. The general DFDC expression gives numerical results in better agreement with experimental data than the expressions from O nsager and Clausius Mossotti relations. In about thirty solvents stron g discrepancies observed mainly arise from specific temperature depend ent effects i.e. association or conformation equilibria.