A DILATOMETRIC INVESTIGATION OF PHASE TRANSITION IN LIQUID CRYSTAL DIMERS

We report here the variation of density across the phase transitions Isotropic ? Nematic, Isotropic ? Smectic A, Nematic ? Smectic A and Smectic A ? Smectic B exhibited by the two homologue of Schiff base liquid crystal dimeric compounds of ,-bis(4-alkylanilinebenzylidene-4-oxy)alkane (m.OnO.m). The compounds studied are 4.O4O.4 and 4.O5O.4. The compound 4.O4O.4 illustrates Smectic A and Smectic B phases, whereas the compound 4.O5O.4 illustrates Nematic and Smectic A phases. The density jumps and peak in thermal expansion coefficient at the transitions confirm the first order nature of the transitions with a density jumps compared to the similar kind of dimeric liquid crystals. The calculated pressure dependence of the transition temperatures using Clausius- Clapeyron equation is also discussed.