Molecular model for the anticlinic smectic-C-A phase

Both phenomenological and molecular-statistical theories of the anticlinic smectic-C-A phase (Sm-C-A) are considered in detail. The anticlinic structu re produces antiferroelectricity in the chiral smectic-C-A phase (Sm-C-A*) The molecular theory is based on a simple model potential which stabilizes Sm-C-A with respect to the synclinic smectic-C phase (Sm-C). Conventional d ispersion and steric interactions between mesogenic molecules generally do not promote Sm-C-A. It may be stabilized by interlayer orientational correl ations between transverse molecular dipoles located in the flexible chains. Such correlations are not sensitive to molecular handedness (chirality), a nd thus the theory accounts for the formation of the anticlinic phase in ra cemic mixtures. The model is also confirmed by other experimental data. Fin ally a simple phase diagram of the perfectly ordered smectic liquid crystal is presented which contains Sm-A, Sm-C, and Sm-C-A.