Anion effects on ionogel formation in N,N′-dialkylimidazolium-based ionic liquids

Addition of an appropriate concentration of water to either 1-decyl-3-methylimidazolium bromide or its nitrate analog is shown to trigger the self-assembly of the ionic liquid (IL) and the concomitant formation of gel (“ionogel”) phases adopting a rich variety of structural motifs. Infrared and 1H nuclear magnetic resonance studies indicate that water addition disrupts hydrogen bonding between the imidazolium ring and the IL anion, and that gelation involves the partial replacement of these bonds with H-bonds between the anion and water. Using small angle X-ray scattering, the relationship of the water content and the nature of the IL anion to the mesoscopic structure of the ionogels has been determined. Of particular note is the observation that by adjustment of the ionogel composition (water content or anion), near-monodomain materials can be formed with either lamellar, 2-D hexagonal or 3-D cubic structures with tunable lattice dimensions.