Polymerization of Counteranions in the Cationic Nanopores of a Cross-linked Lyotropic Liquid Crystal Network to Modify Ion Transport Properties

The nanopores of an as-synthesized cross-linked, cationic, type I bicontinuous cubic (QI)-phase lyotropic liquid crystal network were modified by exchange of its Br– counteranions in the pores with polymerizable 3-sulfopropyl acrylate anions, which were subsequently photopolymerized in situ. The formed anionic poly(3-sulfopropyl acrylate) chains remain inside the pores even when the material is exposed to 1 M aq. salt solutions. After anionic polymer formation inside the pores, the QI network loses its overall ion exchange capacity, presumably because of complexation of the cationic matrix with the resident anionic polymer, and exhibits higher KCl sorption. However, the pore environment remains ionic, as confirmed by water and salt sorption measurements. Single-salt diffusion dialysis studies on supported QI thin film membranes containing the anionic polymer in the QI pores show that KCl permeates >70 and >150 times faster than K2SO4 at 0.05 and 0.5 M feed concentrations, respectively. In contrast, KCl permeates at the same or slower rate than K2SO4 through as-synthesized supported QI thin film membranes. The poly(3-sulfopropyl acrylate) formed inside the QI pores is likely responsible for these observed ion sorption and transport differences.