Anisotropic proton-conducting membranes prepared from swift heavy ion-beam irradiated ETFE films

Kimura, Yosuke*; Chen, J.; Asano, Masaharu; Maekawa, Yasunari; Katakai, Ryoichi*; Yoshida, Masaru

Poly(ethylene-co-tetrafluoroethylene) (ETFE) films were irradiated by swift heavy ion-beams, followed by pre-irradiation for radiation grafting of styrene onto the ETFE films and sulfonation of the grafted ETFE films to prepare highly anisotropic proton-conducting membranes. The fluence of Xe ions and the addition of water in the grafting solvent were examined to determine their effect on the proton conductivity of the resultant membranes. It was found that the polymer electrolyte membrane prepared by grafting the styrene monomer in a mixture of isopropanol and water to the ETFE film with a ion-beam irradiation fluence was a highly anisotropic proton-conducting material, as the proton conductivity was 3 or more times higher in the thickness direction than in the surface direction of the membrane.