Physical properties of oriented thin films formed by the electrostatic complexation of sulfonated polyaramid

The electrostatic complexation of rigid poly(p-sulfophenylene-terephthalamide) (S-PPTA), which forms needle-like aggregates in solution, with flexible poly(allylamine hydrochloride) (PAH) resulted in the formation of aligned polymer films. Proton conductivities of a 20:1 S-PPTA:PAH complex membrane were found to be strongly dependent on both the temperature and humidity, reaching a value of approximately 0.2 S cm(-1) at 90 degrees C, which surpasses that of Nafion. In order to investigate the influence of PAH on the structure of S-PPTA films, microscopy and X-ray scattering analysis was conducted. Optical polarization microscopy images were less birefringent for the complexed samples than the pure S-PPTA, which appeared to be the result of a reduction in the size of the ordered domains. However, X-ray analysis revealed that PAH complexation has almost no effect on the direction and degree of the rigid polymer alignment in the film: S-PPTA is aligned homeotropically, where the polymer chains are perpendicular to the surface of the film. Proton conductivity and polymer orientation in the film were essentially found to be independent of the complex composition, up to mole ratios of 10:1 S-PPTA:PAH.