FERROELECTRIC LIQUID-CRYSTALS FROM ACHIRAL MOLECULES

THE electrical and optical properties of ferroelectric liquid crystals make them of considerable technological interest1. Although the symmetry of most liquid crystalline phases is too high to allow spontaneous polarization, it has long been recognized that a tilted smectic phase made up of chiral molecules can be ferroelectric, owing to a reduction in the overall symmetry of the material2. This forms the basis for conventional ferroelectric liquid crystals, in which the bulk polarization lies within the plane of the smectic layers. Here we describe a new class of organic ferroelectrics composed of achiral 'polyphilic' molecules3,4. Ferroelectricity is demonstrated by measurements of an acoustically induced piezoelectric response and the determination of repolarization currents. The mechanism by which the polar phase is generated differs from that found in conventional chiral smectics, and should in principle allow the preparation of a phase in which the bulk polarization is parallel to the long axis of the constituent molecules.