3D Interconnected Ionic Nano-Channels Formed in Polymer Films: Self-Organization and Polymerization of Thermotropic Bicontinuous Cubic Liquid Crystals

摘要

Thermotropic bicontinuous cubic (Cub_(bi)) liquid-crystalline (LC) compounds based on a polymerizable ammonium moiety complexed with a lithium salt have been designed to obtain lithium ion-conductive all solid polymeric films having 3D interconnected ionic channels. The mono-mer shows a Cub_(bi) phase from -5 to 19 ℃ on heating. The complexes retain the ability to form the Cub_(bi) LC phase. They also form hexagonal columnar (Col_h) LC phases at temperatures higher than those or the Cub_(bi) phases. The complex of the monomer and LiBF_4 at the molar ratio of 4: 1 exhibits the Cub_(bi) and Col_h phases between -6 to 19 ℃ and 19 to 56 ℃, respectively, on heating. The Cub_(bi) LC structure formed by the complex has been successfully preserved by in situ photopolymerization through UV irradiation in the presence of a photoinitiator. The resultant nanostructured film is optically transparent and free-standing. The X-ray analysis of the film confirms the preservation of the self-assembled nanostructure. The polymer film with the Cub_(bi) LC nanostructure exhibits higher ionic conductivities than the polymer films obtained by photopolymerization of the complex in the Col_h and isotropic phases. It is found that the 3D interconnected ionic channels derived from the Cub_(bi) phase function as efficient ion-conductive pathways.