Structures and Properties of the Chiral Smectic C Liquid Crystal Phases Ferro- and Antiferroelectricity in Soft Matter

Doctoral thesis, 2002

Liquid crystals constitute a form of soft matter possessing lower symmetry than isotropic liquids but higher symmetry than solid crystals. In smectic A and C liquid crystals, the rodlike molecules are arranged in layers and the medium has crystal order in one dimension and liquid order in the other two. Liquid crystals with a spontaneous electric polarization were discovered in 1975 and five years later it was realized how to turn them into truly ferroelectric samples. The phase where spontaneous polarization appears is the chiral smectic C phase, i.e. a phase which lacks mirror symmetry and where the long molecule axes are inclined with respect to the layer normal. Materials exhibiting this phase are therefore often referred to as ferroelectric liquid crystals (FLCs). It was realized at an early stage that FLCs can be extremely useful in high-speed, high-resolution electrooptic devices, such as flat panel displays and the research in the field of chiral smectics greatly expanded. In 1989 this led to the discovery of antiferroelectric liquid crystals (AFLCs). Also these belong to the class of chiral smectic C, but it was now realized that this class had to be subdivided into several different phases. Although a number of FLC devices have now reached the market and several prototype AFLC displays have been shown, many fundamental problems still have to be solved before the inherent rich potential of the FLC and AFLC technology could be fully developed. Most of these problems have to do with our lack of understanding of the nature of the major physical phenomena involved. In the present thesis special emphasis is given to issues and concepts like symmetry, order, chirality and polarity. Numerous materials problems are also being addressed, like phase-sequence, confinement, surface-controlled phase-behavior, non-shrinking smectic layer materials, and chemical as well as optical purity – all with the general aim to comprehend the subtle balance between synclinic and anticlinic, between polar and antipolar, order in liquid crystals.