A simple model for phase transitions in antiferroelectric liquid crystals

We propose a phenomenological model which accounts for the entire sequence of subphases exhibited by antiferroelectric smectic liquid crystals. It incorporates, up to the second neighbour, both chiral and nonchiral interactions between the smectic layers. Phase diagrams are presented as functions of appropriate parameters. Some predictions of the model are: i) an intermediate nonuniform modulated phase (FII) in which the difference in the azimuthal angles between neighbouring layers has two different values for adjacent pairs of layers, ii) re-entrance of the ferrielectric phase, iii) critical end points in transitions between phases with the same global symmetry, and iv) tricritical points in transitions involving the FII phase.