ON THE ELASTIC FREE-ENERGY OF SMC-STAR AND SMCA-STAR PHASES

Complete elastic free energy expressions for ferroelectric SmC* and antiferroelectric SmCA* phases are derived within a quadratic expansion in terms of the spatial derivatives of the biaxial tensor order parameter Qij as well as an orthogonal triad. It is found that there exist 25 non-chiral terms, 5 of which are found to be eventually reduced as certain surface contributions, and 5 chiral terms in bulk elastic energy. As a few simple applications of the present free energy, the SmCA*-SmC* phase transition is discussed and the helical pitch in SmCA and SmC* phases is explicitly derived in terms of the molecular tilt angle and the microscopic order parameters. © 1991, Taylor & Francis Group, LLC. All rights reserved.