Theoretical and experimental study of the intermediate SmCFI2* and the SmCFI1* phases in antiferroelectric liquid crystals

Within the new phenomenological model of antiferroelectric liquid crystals, structures of the two phases, the Sm C-FI2* and the Sm C-FI1z* that appear in the temperature range between the Sm C* and the Sm C-A* phase, are found. The structure of the Sm C-FI2* and the Sm C-FI1* phases is consistent with extensive optical, electro-optic, and dielectric measurements performed on the liquid crystal R-10OTBBB1M7, for which resonant x-ray scattering studies have previously proven that these two phases have the three-layer (Sm C-FI1*) and the four-layer (Sm C-FI2*) periodic structure, respectively. The biaxiality of the four-layer structure of the Sm C-FI2* phase is directly observed experimentally for the first time at the temperature where the optical pitch is unwound. The theoretical model allows for experimentally consistent phase sequence, the order of transitions, and the temperature dependence of optical properties including the optical helicoidal modulation inversion within the temperature range of the Sm C-FI2* phase. (C) 2002 American Institute of Physics.