Cyclodextrin-based liquid crystals: A novel approach to promote the formation of thermotropic cubic mesophases and their potential applications as electrolytes

We report the synthesis and mesomorphic studies of a family of amphiphilic β-cyclodextrin derivatives that are polyesterified at the secondary face with either 14 lauroyl or 14 stearoyl chains (apolar), and 7 tri- or tetra-ethylene glycols (polar) at the primary face. The end of each tri- and tetra-ethylene glycol chain is further modified with different terminal functionalities in term of their dipole moment (O-methyl vs O-acetyl vs O-2-cyanoethyl). This has generated several subgroups of amphiphilic β-cyclodextrin derivatives with a systematic change of their relative volumes of the hydrophobic and hydrophilic regions. Our studies showed that all these derivatives self-assemble into thermotropic liquid crystals, with the majority forming hexagonal column mesophases while three compounds form a bicontinuous cubic phase. We rationalized the mesomorphic behaviour of these compounds in term of the relative total van der Waals fractional volumes occupied by the hydrophilic and hydrophobic chains. Upon added with LiTFSI, the formed bicontinuous cubic phase (as a pure compound) was found to transition to form the more stable smectic A mesophase (composite), and both solid NMR studies and impedance spectroscopy revealed that these novel amphiphilic β-cyclodextrin-based liquid crystalline materials have the potential to be used as efficient electrolytes for lithium conduction.