Transport properties of Nafion (R)/cyclodextrin membranes

The transport properties of Nafion(R)/cyclodextrin membranes were studied f or simple gases and water. Cyclodextrins (CD) in ionic form have been intro duced as counter-ions in the ionic phase of Nafion(R) by solution exchange. The CD and Nafion(R) transport parameters were at first determined using s orption methods. The cyclodextrin gas and water solubility coefficients are higher than the Nafion(R) ones but the diffusion coefficients are lower. F or the Nafion(R)/CD composite properties, the gas permeability and diffusio n decrease with the CD content showing that the free volume of the cyclodex trin molecules is not accessible to the diffusant molecule. Moreover the de tailed analysis of the permeation and sorption data shows that gases do not diffuse through the Nafion(R) ionic zone. A similar decrease as a function of the cyclodextrin content is obtained on the water diffusion and permeab ility whereas it is known that water diffuses through the ionic phase. This behaviour has been explained by the fact that cyclodextrins reduce the wat er swelling capacity of this ionic phase and modify its reference transport properties. A small angle neutron scattering (SANS) microstructural analys is of the composite membrane confirms this phenomenon. (C) 2001 Elsevier Sc ience B.V. All rights reserved.