Dipolar Aggregation and the Static Dielectric Permittivity of Some Liquid Crystalline Materials

Abstract

In the paper, we show how some modifications in the chemical structure of mesogenic molecules can lead to an essential increase of the dielectric permittivity of liquid crystalline material due to the reduced molecular ability to the antiparallel dipolar aggregation. As an example, the static permittivities of two nematogenic homologous series, CnH2n+1PhPhCN and CnH2n+1PhCOOPhCN, are analyzed. However, the structural modifications of mesogenic molecules lead often to unfavorable changes in some important physical properties of liquid crystalline material, as a shift in the clearing temperature, for example, or can lead even to a disappearance of the mesophase. This paper presents such an event observed for the compound composed of C5H11PhPh(CH3)CN molecules, the methyl derivatives of C5H11PhPhCN molecules, which form a well-known nematic liquid crystal.