Phase transitions and molecular properties of new divinyl and diepoxy compounds

Abstract

The aim of this paper is to compare some physical properties of six new divinyl and diepoxy compounds. The compounds differ in the length of the rigid central segments. Optical observations and differential scanning calorimetry confirmed the existence of a mesophase in five compounds and enabled the determination of the phase transition temperatures. The wide angle X-ray scattering (WAXS) measurements of samples aligned in a magnetic field and the optical observations allowed the identification of the mesophase types. In four compounds a nematic mesophase was detected during both heating and cooling. In one case two higher ordered phases were observed during cooling. The analysis of WAXS images and the positions and shapes of the scattering intensity peaks suggests a smectic B–crystal E transition. Using the data obtained in WAXS measurements carried out in the nematic phase, the lengths of the molecules and the average nearest neighbour distances were estimated. The average intermolecular distances and the layer spacings were also estimated for the SmB and E phases. The lengths of the molecules were also calculated by means of theoretical ab initio methods. The results obtained are in very good agreement with the experimental data.