Preparation and structural characterization of shear-aligned films in a high proton conductive alkyl-sulfonated polyimide with lyotropic liquid crystallinity

Molecular-organized structures of polymer electrolytes have been extensively studied in recent years. Recently, we demonstrated that alkyl-sulfonated polyimide (ASPI) forms a lyotropic lamellar liquid crystalline (LC) phase under humid conditions and exhibits a high proton conductivity of 10−1 S cm−1 in the in-plane lamella direction at 95% relative humidity. In this work, we conducted precise structural evaluations of the lyotropic LC ASPI for in-plane aligned films prepared by a bar-coating method with a concentrated solution. The ASPI concentrated solution exhibited a birefringent feature and lyotropic LC properties. Humidity-controlled in situ polarized infrared spectroscopy confirmed the in-plane anisotropic structure of the aligned film with clear dichroism, and the dichroism did not change under humidification. Humidity-controlled in situ grazing-incidence X-ray scattering measurement revealed the hierarchical LC structure with main-chain smectic ordering in the lyotropic lamella structure of the shear aligned ASPI film.