Controlled modification of Nafion membrane with cationic surfactant

Abstract

Controlled modification of Nafion 112 membrane with oppositely charged micelle-forming surfactant, dodecylpyridinium chloride (DPC), has been carried out by immersion of the membrane in dilute DPC aqueous solution. All sulfonic groups of Nafion are available for ion-exchange binding with the surfactant ions, the membrane modification degree being determined by the [DPC]/[SO3−] ratio. DPC binding is accompanied by hydrophobic interactions of its alkyl chains and results in the formation of intramembrane micellar phase. The modified membranes are extraordinarily stable in water and aqueous solutions of H2SO4 (at least, 2.5 M), NaCl (at least, 3 M), and propanol-2 (at least, 40 vol.%), owing to the binding enhancement by Nafion hydrophobic matrix. Surfactant uptake significantly decreases equilibrium water content (from 33% down to 4%), proton conductivity (by up to two orders of magnitude), and vanadyl ions permeability (by up to four orders of magnitude) of the membrane, improving its ion selectivity.