Self-Assembled and Polymerized Hierarchical 2D Nanostructures of Phosphonic Acid Reactive Mesogens for High-Temperature Anhydrous Proton Transport

For the development of proton exchange membranes (PEMs), particularly for high-temperature anhydrous proton transport, a phosphonate polymerizable amphiphile (PPA) is newly synthesized. To fabricate an anhydrous proton conductive (APC) polymer-stabilized film, PPA is combined with a liquid crystal (LC) crosslinker in a 6:4 weight ratio, forming an LC reactive mesogen (LCRM) mixture. This mixture self-assembles under uniaxial orientation in the smectic mesophase, and subsequent photopolymerization generates continuous and aligned proton transport pathways within the hierarchical two-dimensional (2D) nanostructure film. The resulting polymer film exhibits high proton conductivity at elevated temperatures, with anisotropic transport properties dictated by molecular orientation. Furthermore, the proton conductivity can be finely tuned by manipulating the molecular self-assembly at the nanoscale and the molecular orientation at the macroscale. A comprehensive understanding of the interplay between molecular packing structure, macroscopic molecular orientation, and proton transport behavior in APCs demonstrates the critical role of precise functional group positioning in establishing efficient proton conduction pathways. The hydrophobic nature, high thermal stability, and exceptional chemical durability of these proton-conductive films further emphasize their potential as next-generation materials for high-temperature PEM applications.