Nafion® 117 modified by low dose EB irradiation:: surface structure and physical properties

Recent progress in the treatment of Nafion(R)117 film by low dose electron beam (EB) exposure is described. The effect of EB exposure between 0 and 400 muC cm(-2) doses is discussed on a structural level and a dual reaction mechanism, involving cleavage of the hydrophilic side chain and subsequent formation of -CO2H units at the site of the polymer backbone, proposed for this system. This work was extended by consideration of the effects of EB irradiation in the presence of different oxygen concentrations, 50 ppm, 550 ppm and 2000 ppm. From these studies we conclude that low dose EB exposure facilitates replacement of the sulfuric acid moieties, located at the terminus of the Nafion(R) side chain, with carboxylic acid units as the dominant hydrophilic group found in the pores of the ion channels at the Nafion(R) surface. It has been demonstrated that by increasing the degree of carboxylic acid formation at the site of the polymer backbone the conductivity of the resultant material can be buffered sufficiently so as to compensate for the effect of the subsequent cleavage of the hydrophilic side chains. This result not only confirms the irradiation mechanism postulated but allows significant advantages in the development of membranes with properties optimised for DMFC performance.