RESUMEN
The unwinding of the short pitch helical smectic-C*alpha structure in an external electric field is studied within a discrete phenomenological model. It is found that the pitch increases quasicontinuously at low electric fields and is commensurate with the smectic layer thickness at any field. The sequence of stable structures recalls the once popular and then abandoned devil's staircase model. At larger fields the pitch grows discontinuously in steps of one smectic layer, forming a harmless staircase. Taking into account the achiral next-nearest-layer interactions the final transition to the unwound structure is found to be discontinuous.
RESUMEN
Anticlinic smectic-C surfaces were found experimentally as ground state structures in free-standing films made of smectic liquid crystals with no anticlinic bulk phases. A mean-field interpretation of this observation is given within a discrete phenomenological model of antiferroelectric liquid crystals, which additionally considers the enhanced order present at the surfaces of the free-standing films. The temperature dependence of the critical electric field that drives the transition between the anticlinic and synclinic smectic-C surfaces is evaluated, and fair agreement with the experimental data is found.