Phase Transition Studies of 6.O12O.6 and 7.O6O.7 Using Density Measurements

Abstract

The symmetric liquid crystal dimer homologous series, α,ω-bis-(4-n-alkylaniline benzylidene-4′-oxy) alkanes, show a rich variety of smectic polymorphism. We report here the nature of different transitions exhibited by two of these dimers using density measurements as a function of temperature. The compound 6.O12O.6 exhibits only nematic phase; while 7.O6O.7 exhibits smectic A and smectic F phases. All the phase transitions studied viz., isotropic – nematic, isotropic – smectic A, and smectic A – smectic F are confirmed to be of first order nature. The calculated density jumps, thermal expansion coefficient data and pressure dependence of transition temperatures are analysed in the light of available literature data.

Keywords:

• Isotropic – nematic transition
• isotropic – smectic A transition
• smectic A – smectic F transition
• symmetric dimer

Acknowledgment

Authors are thankful to CSIR, New Delhi for financial support and to Professor P. K. Tripathi, Head of the Department of Chemistry for allowing us to use the Differential Scanning Calorimeter.