Synthesis and characterization of imidazolium-based polymerized ionic liquid crystals containing cholesteryl mesogens

Abstract

A series of polymerized ionic liquid crystals (PILCs) with different anions were synthesized and characterized, including bromides (PIBs), tetrafluoroborates (PITs), hexafluorophosphates (PIHs), trifluoromethanesulfonates (PITFs), and bis(trifluoromethylsulfonyl)imides (PIBTs). The PIBs show both smectic A (SmA) phase and chiral nematic (N*) mesophases on heating and cooling cycles, but other PILCs exhibit only chiral nematic mesophase. The glass transition temperature (Tg) of the PIBs, PIHs, PITs, PITFs, and PIBTs decreases successively, but the isotropic temperature (Ti) shows no big change. All these PILCs display ionic conductivity in mesophase. The PITs present a little higher ionic conductivity than other PILCs indicating that the ionic conductivities of these PILCs depend on the nature of the anions. The molecular packing of these PILCs is distinct from each other due to different anions. The bromides (PIBs) should form intimate ion pairs, but other PILCs should form ion clusters rather than ion pairs due to large size of anions.