DIPOLE ASSOCIATION OF POLAR MESOGENS IN A LIQUID-CRYSTAL SOLVENT

This paper reports results of a detailed examination of the low freque ncy dielectric properties of dilute anisotropic solutions of two polar mesogens, 4-cyano-3-fluorophenyl-4'-propylbenzoate (C3FCN) and 4-cyan ophenyl-4'-butylbenzoate (C4CN), as solutes in a non-polar liquid crys tal solvent. At low concentrations the effects of dielectric screening are minimised, and the association of mesogens due to dipole-dipole f orces can be studied. The measurements suggest that at very low concen trations the dipole-dipole interactions result in a small increase in the effective dipole moment, while at higher concentrations local anti ferroelectric order becomes dominant. The results are fitted to an ass ociation model, which was originally developed to describe the dielect ric behaviour of isotropic solutions of polar solutes (alcohols) in ca rbon tetrachloride solutions.