Landau model for polymer-stabilized ferroelectric liquid crystals: Experiment and theory

The interaction between a phase separated polymer network and a liquid crystal was studied across the smectic-A(*) (Sm-A(*)) to smectic-C-* (Sm-C-*) phase transition of a polymer-stabilized ferroelectric liquid crystal polymerized in the Sm-A(*) phase. Using precise measurements of the tilt angle and the spontaneous polarization as functions of the external electric field and polymer concentration, the effective coefficients of the Landau expansion of the free energy of the Sm-C-* phase have been determined experimentally. The observed polymer concentration dependence of the Landau expansion coefficients is explained using a more general theoretical model which incorporates the effect of polymer networks on the local liquid crystal director configuration. In particular, using experimental estimates of the penetration depth of the polymer network into the liquid crystal, it is shown that the b coefficient calculated from the Landau model increases with polymer concentration, evidencing the relationship determined experimentally.