Phases, phase transitions and confinement effects in a series of antiferroelectric liquid crystals

Abstract

Using a variety of optical and electro-optical techniques, as well as dielectric spectroscopy, we have investigated three homologues in the chiral liquid crystal series nF1M7, where n denotes the length of the unbranched terminal chain. The main focus of the study is the series of smectic C subphases, i.e. SmC^* _α, SmC^* _1/3 and SmC^* _¼. During switching in the SmC^* _α phase, a peculiar redirection of the plane of biaxiality, distinguishing this phase from SmA^* and SmC^*, was observed. We present a simple explanation for this behaviour which correlates well with the clock model description of the SmC^* _α phase. We found a zero mesoscopic polarization for the SmC^* _¼ phase and a non-zero mesoscopic polarization for SmC^* _1/3, observations which are consistent with a distorted clock model. The dielectric spectroscopy investigations, performed at several different cell gaps, clearly show that the dielectric response in these materials is easily dominated by surface-induced structures if the cell gap is reduced, thus reflecting that the bulk thermodynamic phase exists in very thick cells only.