A unidomain membrane prepared from liquid-crystalline poly(pyridinium 4-styrene sulfonate) for anhydrous proton conduction

Abstract

Liquid-crystalline poly(pyridinium 4-styrene sulfonate) was synthesized through an acid-base reaction between poly(4-styrene sulfonic acid) and a mesomorphic pyridine derivative. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements revealed that the resultant polymer exhibited a bilayer smectic order with a d-spacing of 10.2nm at temperatures above 193°C. Thermogravimetric (TG) analysis indicated that the polymer was thermally stable at temperatures up to288 °C. A solution-cast membrane of the polymer was mechanically sheared in the smectic A phase to obtain a unidomain membrane with a thickness of 0.15mm. Polarizing optical microscope (POM) and scanning electron microscope (SEM) images confirmed that the smectic bilayers in the unidomain membrane were perpendicularly to the shearing direction. Electrochemical characterization suggested that the uniformly lamellar pathways formed in the uni-domain membrane favored anhydrous proton conduction. The maximum proton transference number and conductivity of the membrane reached 0.46 and 7.0×10−6Scm−1, respectively. The temperature dependence of the proton conductivity followed the Arrhenius law and the estimated activation energy for the anhydrous proton conduction across the membrane was 60kJmol−1.