Amino acid-derived protic ionic liquids: Physicochemical properties and behaviour as amphiphile self-assembly media

Abstract

The thermal phase transitions and physicochemical properties of a series of 21 amino acid-derived protic ionic liquids and four protic molten salts have been investigated. Structureproperty comparisons for this series were investigated for alkyl- and cyclic amino acid cations, and ethoxy and methoxy groups on the cation, combined with nitrate or various carboxylate-containing anions. All the protic fused salts were found to be 'fragile'. Most of the protic fused salts exhibited a glass transition, with the transition temperatures ranging from -90° to -42°C. Viscosities and conductivities ranged from 0.03 to 15.46Pas and 0.02 to 2.20mScm-1 at 25°C respectively. The protic ionic liquids alanine methyl ester glycolate, proline methyl ester nitrate, and proline methyl ester glycolate were found to be capable of supporting amphiphile self-assembly. Lamellar or hexagonal liquid crystalline phases were observed with the cationic surfactant hexadecyltrimethylammonium bromide and the non-ionic surfactant Myverol 18-99K. © 2011 CSIRO.