Mean-field study of uniaxial smectic liquid crystals with polarized layers

A mean-field calculation based on a simple model is reported. The numerical results indicate that only a relatively small polar interaction is required to induce a transformation from a nonpolar uniaxial smectic phase (smectic $A$) to a uniaxial smectic phase with polar layers within a reasonable temperature range. The polar order may accompany the smectic phase in all or in part of its range of existence. Arora, Taylor, and Ferguson (ATF) observed that some compounds show two phases with the smectic-$A$ morphology and suggested that the lower-temperature phase has polar order. Our results can reproduce the main features as far as the transition temperatures are concerned. The small transition entropies reported by ATF are in agreement with our results; however, there are not enough data to permit any correlation with the model parameters.