Comportement dipolaire de fluides moléculaires jusqu'au point critique I. La polarisation statique

Abstract

We report here measurements of the static permittivity as a first step in a dielectric study of rotational motion in liquids up to the critical point. The decrease of the static dielectric constant has been measured along the liquidgas coexistence curve for the liquids C₆H₅Cl, C₆H₅F, C₆H₆, CHCl₃, CFCl₃, CCl₄, SCO and CS₂. In the discussion we focus our attention on the behaviour of Kirkwood's correlation factor g. Our results confirm its dependence on the steric configuration of the molecule, especially on the orientation of the dipole axis in relation to the shape of the molecule, and show that the value of g for the liquid phase changes with the temperature, approaching unity at the critical point, while its value is unity at all temperatures at the densities of the coexisting vapour.