The swelling behaviour of perfluorinated ionomer membranes in ethanol/water mixtures

The microscopic and bulk swelling of "Nafion(R)" perfluorinated ionomer mem branes in mixtures of ethanol and water was studied using small angle X-ray diffraction and optical microscopy. The microscopic swelling decreased wit h increasing ethanol content, in contrast to the bulk swelling which increa sed dramatically, reaching a maximum in a mixture containing 75% ethanol an d 25% water. Uniaxially oriented membranes swollen with such an optimal mix ture were found to relax back to an almost isotropic state, which could not be achieved by using water alone. The conclusion is that the ethanol plast icises the fluorocarbon matrix in Nafion, allowing the ionic material to be redistributed into smaller, more numerous clusters than in membranes swoll en with water alone. (C) 2000 Elsevier Science Ltd. All rights reserved.