Chiral smectic C subphases induced by mixing a bistereogenic antiferroelectric liquid crystal with a non-chiral liquid crystal

By mixing a bistereogenic antiferroelectric liquid crystal (AFLC) compound, exhibiting only the SmQ* and SmCa* mesophases, with the achiral N-SmC liquid crystal HOAB we could induce all three AFLC SmC-type subphases, SmCalpha*, SmCbeta* and SmCgamma*. This seems to be in contradiction with two recent postulations regarding the subphase stability, one of which suggests that the subphases appear as a result of strong chiral interactions, the other that these phases require high smectic order something one would generally not expect in mixtures. We have studied the helical pitch, optical tilt angle, spontaneous polarization and the x-ray diffraction due to the smectic layering, as a function of mixing ratio in order to better understand the relation between phase sequence and mixture composition. The smectic layer spacing shows a strongly non-linear behavior suggesting that the basic structure of the pure AFLC substance is retained up to a HOAB content of about 75%.