A new series of siloxane liquid crystalline dimers exhibiting the antiferroelectric phase

In this paper, we report the study of a new series of symmetric chiral liquid crystalline siloxane dimers, their related monomers, and two of those monomers with heptamethyltrisiloxane attached. All the dimers coupled with a trisiloxane show the SmC_A phase, which in several cases has a large tilt angle greater than 40° over a wide temperature range, as well as high spontaneous polarisation in the field-induced ferroelectric state. Spacer lengths of 3-6 and 11 carbons between the siloxane central unit and the mesogenic cores were used. Monomers with 3-6 carbons in the spacer showed only orthogonal phases while the monomer with an 11-carbon spacer, as well as the monomers with siloxane attached, have a high tilt angle ferroelectric phase. The materials were characterized by means of DSC, NMR, X-ray diffraction, electro-optical methods (tilt angle and texture characterization) and polarization measurements.