A simulation study of field-induced proton-conduction pathways in dry ionomers

The morphological changes that can be induced in a dry ionomer by application of a strong electric field have been studied by means of computer simulation. The internal energy of the membrane at first slowly decreases with increasing field, but then rapidly increases after a certain threshold field is reached. This effect is interpreted as the reorganization of interacting head group dipoles in response to the external perturbation. The resulting morphology contains continuous channels of hydrophilic material capable of facilitating proton conduction. Upon removal of the poling field, the system does not return to its original morphology, but retains the anisotropic structure of the poled material. The poled structure appears to be thermodynamically stable, as confirmed by calculations of the Helmholtz energy of the original and poled samples.