Anisotropic Proton Conduction in Aligned Block Copolymer Electrolyte Membranes at Equilibrium with Humid Air

Abstract

The effect of alignment of proton-conducting domains ill hydrated poly(styrenesulfonate-b-methylbutylene) copolymer films oil conductivity,,vas Studied by impedance spectroscopy. Pressing isotropic samples obtained by casting results in lamellae aligned ill the plane of the film, Application of electric fields and now fields oil the isotropic samples results in lamellae aligned perpendicular to the plane of the film. The alignment of lamellae, quantified by a combination of two dimensional small angle X-ray scattering (SAXS), birefringence, and transmission electron microscopy (TEM), was much better in the pressed samples than in the field-aligned samples. Conductivity was Measured in the plane of the film (sigma(parallel to)) and normal to the plane of the film (sigma(perpendicular to)). Only the pressed sample showed highly anisotropic proton conduction With sigma(parallel to)/sigma(perpendicular to) = 75. In this case, the value of sigma(parallel to) increased by 30% after alignment, relative to that obtained from the as-cast samples. The values of sigma(parallel to)/sigma(perpendicular to) obtained after electric Field and shear field alignment were 1.2 and 1.4, respectively, in spite of partial alignment of the domains. and the increase in sigma(perpendicular to) after alignment was less than 20%.