Effect of polymer network on thermodynamic stability and switching behavior of the smectic-C_{α}^{*} phase.

A polymer-stabilized liquid crystal based on 4^{'}-(octyloxy)biphenyl-4-carboxylate 2-fluoro-4-((octyl-2-yloxy)carbonyl)phenyl (D16) and 1,6 hexanediol diacrylate as a monomer was prepared by in situ photopolymerization. The selected antiferroelectric liquid crystal contains a fast-switching smectic C_{α}^{*} phase (SmC_{α}^{*}), and the influence of the polymer network on the thermodynamic stability of this phase and its switching behavior under applying time-dependent electric field were studied. Using dielectric spectroscopy and polarizing microscopy, the liquid crystal materials were characterized, and subsequently with the use of the reversal current method (RCM) the current response, especially from the SmC_{α}^{*} phase was carefully analyzed. The current response is complex and also depends on the neighboring liquid crystal phases. In the liquid crystal-polymer system, as well as in the liquid crystal-monomer mixture, a significant shift of the temperature range of the SmC_{α}^{*} phase toward lower temperatures was observed; however, the thermodynamic instability related to the transformation to the crystalline phase was also noted and characterized. Because of the fuzzy phase transitions detected in the liquid crystal-polymer system by dielectric spectroscopy and also because of the lack of the characteristic dielectric signature of SmC_{α}^{*} after polymerization, we proposed the use of the RCM, as a complementary one, to identify the SmC_{α}^{*} phase even in such complex materials.