Gyroid nanostructured soft membranes formed by controlling the degree of crosslinking polymerization of bicontinuous cubic liquid-crystalline monomers

Abstract

The self-organization of liquid-crystalline monomers and subsequent polymerization is a unique strategy for creating nanostructured polymer membranes with novel functions and innovative properties. In this study, we developed gyroid nanostructured soft polymer films based on this strategy. Two types of amphiphile zwitterion monomers were designed and synthesized: a single-type amphiphile zwitterion monomer (S-ZI) and a gemini-type monomer (G-ZI). These compounds show liquid-crystalline behavior in the presence of bis(trifluoromethanesulfonyl)imide (HTf2N) and water. We attempted to find an appropriate mixing ratio of S-ZI and G-ZI that satisfied the following two criteria: suitability for the exhibition of bicontinuous cubic (Cubbi) phases and acquisition of self-standing properties and softness. The 25/75 wt% component ratio of S-ZI/G-ZI was found to meet these conditions. By carrying out a polymerization for the mixture in the above mixing ratio in the Cubbi phase, a polymer film with self-standing properties and resistance to bending was successfully obtained. This film showed a high ionic conductivity of 1.27 × 10−2 S cm−1 under a relative humidity of 90%. A gyroid nanostructured soft polymer film was developed by the co-organization of two types of amphiphile zwitterion monomers and a suitable acid into a bicontinuous cubic liquid-crystalline phase and subsequent in situ polymerization. The obtained polymer film showed a high ionic conductivity of 1.27 × 10–2 S cm–1 at a relative humidity of 90%.