Surface observation of solvent-impregnated Nafion membrane with atomic force microscopy.

Surface morphology modification of the Nafion 117 membrane has been investigated by atomic force microscopy. The effects of water and methanol on the topography and structure of the surface were studied using the contact and tapping atomic force microscopy modes. Nafion topography considerably changes when samples absorb water. However, samples stored in methanol are characterized by flat surfaces. Surface modification was linked to an expansion phenomenon during the swelling of Nafion by solvents. Tapping-mode phase images showed that ionic and cluster domains are distinguishable from the surface of samples impregnated either in water or methanol.