Calorimetric Study of Frustrated Smectic Liquid Crystals

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Professor Garland proposes to carry out high-resolution calorimetric measurements on a variety of polar liquid crystal molecules containing long aromatic cores and on binary mixtures of such molecules. There are two competing order parameters in these systems, and in general they exhibit smectic fluctuations in the nematic phase at two characteristic wavevectors that are incommensurate. Such frustrated compounds can form a wide variety of ordered smectic-A and analogous smectic-C phases. Thus there are many interesting nematic-smecatic transitions and smectic-smectic transitions involving two different smectic-A phases or a smectic-A and a smectic-C phase. An automated, computer-controlled ac microcalorimeter will provide high resolution heat capacity data for second-order phase transitions, special critical and bicritical points, and even weakly first-order transitions. Analysis of such data allows one to characaterize the critical energy fluctuations associated with smectic ordering. The results will test the validity of current theory and should stimulate new and more realistic theoretical models.