Relationship Between Methanol Permeability and Structure of Different Radiation-Grafted Membranes

Styrene grafted and sulfonated poly(vinylidene fluoride) rid poly(vinylidene fluoride-co-hexafluoropropylene) films are candidates as electrolytes in direct methanol fuel culls. Their behaviour in water, 1 and 3 mol dm(-3) aqueous methanol, and pure methanol were studied. According to SAXS results, water and methanol-water solutions have similar effects on the membranes, i.e., the lamellar period increases and the ionic domains enlarge. Furthermore differences in the ionic domain structures in pure methanol and water were observed. These structural changes together with dissimilar liquid uptakes in water and in methanol are reflected is changes in the conductivities. An increase in the SAXS intensity and changes in the Bragg distance of the ionic peak were observed in methanol compared to aqueous solutions. This may be related to the hydrophobicity of the CH3 group on methanol. Dissimilarities in methanol permeability to through the radiation-grafted membrane can be related to structural differences in membranes observed with SAX. Permeabilities were observed to be lower for the radiation-grafted membranes compared to Nation (R) 115, which compensates tor the higher area resistance of the experimental membranes and thus improves their performance in a fuel cell.