Contrast variation small-angle neutron scattering study of the structure of hydrocarbonate polymer electrolyte membrane; Microphase separation and ionic cluster distribution

Zhao, Y.; Koizumi, Satoshi; Rikukawa, Masahiro*; Yoshida, Miru*

We employed contrast variation small-angle neutron scattering method to investigate the morphologies of a newly designed polymer electrolyte membrane, made of multi-block copolymer poly(sulphonate phenylene)-b-poly(arylene ether ketone), which is denoted by S-6H (n) x:y, where x:y means a ratio of the hydrophilic to the hydrophobic blocks. Two scattering maximums were observed at low q and high q regions for wet membranes, where q is a magnitude of scattering vector. The low q maximum is attributed to the formation of microdomains upon swelling, whereas the high q maximum is due to the formation of ionic clusters in the swollen microdomain. These morphologies could be clarified by the contrast variation method, which results in a matching in the scattering contrast either between water mixture (HO/DO) and the swollen microdomains, or between the water mixture and ionic clusters. The further analysis of the scattering profiles indicates that the microdomains are spherical and percolated with each other. Moreover, the ionic clusters distribute homogenously inside the hydrophilic domains.