Controlled self-assembly of amphiphiles in ionic liquids and the formation of ionogels by molecular tuning of cohesive energies

Abstract

In this paper, the self-assembling characteristics of a series of L-glutamate-based ammonium amphiphiles are studied in ionic liquids (ILs). These cationic amphiphiles are dispersible in imidazolium ILs with bis((trifluoromethyl)sulfonyl)amide (TFSA) anion. Amphiphiles-containing didodecyl ester or short dioctyl amide groups were molecularly dispersed in conventional 1-butyl-3-methylimidazolium TFSA, whereas they formed bilayer membranes when they were dispersed in polar, ether linkage-introduced IL. Thus, the modification of ILs exerts a crucial influence on amphiphilic self-assembly. Enhancement of the intermolecular interactions of L-glutamate amphiphiles is achieved by introducing multiple amide bonds and longer alkyl chains, which leads to better self-assembling properties. These amide-enriched amphiphiles form fibrous bilayer assemblies even in conventional ILs with low cohesive energy densities. These observations confirm that the formation of bilayer membranes in ILs is a general phenomenon when the solute molecules have the appropriate ‘ionophilic/ionophobic’ nature. Molecular self-assembly in IL is promoted by controlling cohesive energies of amphiphiles and ILs.