Self-assembly of new surface active ionic liquids based on Aerosol-OT in aqueous media

New anionic ionic liquid surfactants have been synthesized by replacing the sodium cation of Aerosol-OT (sodium dioctylsulfosuccinate, [Na]AOT) with various biocompatible moieties, such as 1-butyl-3-methyl imidazolium ([C(4)mim]), proliniumisopropylester ([ProC(3)]), cholinium ([Cho]), and guanidinium ([Gua]). The Aerosol-OT derived ionic liquids (AOT-ILs) were found fairly soluble in water and formed vesicles above a critical vesicle concentration (CVC) which depended upon the nature of cation, and followed the order: [ProC(3)] < [C(4)mim] < [Gua] < [Cho] < Na. The self-assembly process was characterized using surface tension (ST), isothermal titration calorimetry (ITC), conductivity, dynamic light scattering (DLS), nuclear magnetic resonance (NMR) and transmission electron microscopy (TEM). Unlike other AOT-ILs, a structural transformation has been observed for [C(4)mim]AOT above CVC, because of certain amphiphilic character in the cation [C(4)mim]. Thermodynamic parameters calculated from ITC and conductivity techniques revealed that the vesicle formation process is entropy driven for [C(4)mim]AOT, whereas the process is both enthalpy and entropy driven for other AOT-ILs. In order to check the versatility of synthesized AOT-Ws we have tested their dissolution behavior in a different class of ionic liquids. All the AOT-ILs were found fairly soluble in the hydrophilic IL, ethanolammonium formate (EOAF), whereas only [C(4)mim]AOT and [ProC(3)]AOT were found soluble in hydrophobic IL, [C(4)mim]Tf2N. Such combinations can have potential for construction of stable colloidal formulations or microemulsions in ionic liquid media. (C) 2014 Elsevier Inc. All rights reserved.