Electric-field-induced switchable dark conglomerate phases in a bent-core liquid crystal exhibiting reverse columnar phases

摘要

Electric-field-induced transitions into switchable dark conglomerate (DC) phases from two types of reversencolumnar mesophases have been observed in the bent-core (BC) compound 2,7-naphthylene bis[4-(3-methyl-n4-n-tetradecyloxybenzoyloxy)] benzoate. Optical and x-ray studies show that the higher temperature columnarnphase corresponds to the orthogonal B1rev phase, whereas the lower temperature columnar phase is a variant ofnthe B1revtilt phase. As the layer fragments in this phase are modulated in order to relieve the steric hindrancencaused by an anticlinic tilting in adjacent blocks, it has been named B1revtiltM. The shape of the chiral domains arendifferent in the DC phases viz. DC-B1rev and DC-B1revtiltM obtained by applying the electric field in the B1rev andnB1revtiltM phases, respectively. While the chiral domains in the DC-B1rev phase appear similar to those observednin other DC phases, the shape of the domains in the DC-B1revtiltM phase appear to have some similarity to thendomains in the banana leaf texture in the B1revtiltM phase implying that the detailed structure in this DC phase maynbe different. Optical observations, electro-optics, and dielectric studies show that the DC-B1rev and DC-B1revtiltMnphases are both switchable and possess a local SmCSPF type of structure. As the temperature is decreased thenswitching behavior changes from ferroelectric to antiferroelectric. The temperature at which this changeovernstarts occurring coincides with the temperature at which the layer modulation occurs to overcome anticlinic tiltnand the B1rev to B1revtiltM phase transition takes place without the application of the electric field. The change innswitching behavior is attributed to a transformation into flat layers with the SmCAPA type of structure as alsonevidenced by the nucleation of bright regions alongside the chiral domains.