Importance of quadrupolar ordering in antiferroelectric liquid crystal devices

A model of switching in antiferroelectric liquid crystals is presented which predicts both helix unwinding in the pretransitional regime and a field induced transition to the ferroelectric state. When the ratio of the coefficients of the quadrupolar and dipolar ordering terms in the bulk free energy expression exceeds a critical value, the latter transition becomes first order, in agreement with experimental observation. We have determined these coefficients in the commercial mixture CS4001. The ratios of the coefficients imply that all three states (antiferroelectric and two ferroelectric) are stable in the ground state, i.e., antiferroelectric liquid crystals are truly tristable.