Short range order in the isotropic phase of antiferroelectric liquid crystals

Optical activity measurements in the isotropic phase of two antiferroelectr ic liquid crystal systems in which the chirality can be varied reveal unusu al behaviour of the short range order. In one system the phase sequence as the chirality is increased is smectic A, smectic C-A*, and smectic Q. In th e other system the phase sequence is smectic C*, smectic C-A*, and smectic Q as the chirality is increased. The short range order of the isotropic pha se behaves similarly for these systems, showing mean field behaviour at low chirality and far above the phase transition, but deviating from this beha viour significantly as the chirality is increased and the phase transition is approached. These optical activity results indicate how different is the short range order in the isotropic phase for these antiferroelectric liqui d crystal systems acid demonstrates the crucial role played by chirality. P ast theoretical work that includes smectic-like fluctuations in the calcula tion of short range order in the isotropic phase is capable of qualitativel y explaining these results.