We have studied the polar structures in the binary mixtures of bent-core liquid crystals P-n-O-PIMB(n-2)*-(n-4)O showing the ferroelectric smectic- CAPF (Sm-CAPF) (n=8 and 10) and antiferroelectric ...Sm-CSPA (n=9) B2 phase. Although the polar structure of the one-to-one mixture is governed by the compound with longer end chains, it is much more complicated in the mixtures with slightly less fraction of compounds with longer end chains. Even if the mixtures show the antiferroelectric phase before field application, the ferroelectric domains remain once the field is applied and coexist with the antiferroelectric domains. The coexistence structure was modeled by comparing the microscope real image with that of second-harmonic generation. The fraction of the ferroelectric domains is larger at higher temperature region of the B2 phase and decreases with decreasing temperature. The stable phase structures were discussed based on the phenomenological theory. We suggest that the coupling energy of the layer chirality is higher than the energies of the orientation correlations of tilts and polarizations between adjacent layers.
We examined the detailed phase structures of two kinds of swallow-tailed bent-core homologues; i.e., P7-O-PIMB-4O-nEt (n=5, 6) and P8-O-PIMB-4O-nPr (n=5, 6) (see Fig. 1) by means of texture ...observations, switching currents and second harmonic generation (SHG) measurements. Both P7-O-PIMB-4O-5Et and P8-O-PIMB-4O-5Pr exhibited circular domains which had stripes in the absence of a field. The stripes disappeared by applying a field, indicating the SmCSPAphase. We confirmed the antiferroelectricity by two switching current peaks in polarizing reversal current measurements and an electric-field-induced SHG with a threshold and a hysteresis on increasing and decreasing the field. On the other hand, in P7-O-PIMB-4O-6Et and P8-O-PIMB-4O-6Pr, we observed spiral and myelinic-like texture, suggesting the B7 phase. The details will be presented.
