Interaction of imidazolium based ionic liquids with Triton X-100 micelles: investigating the role of the counter ion and chain length†
The micellar characteristics of an aqueous solution of the polyoxyethylene based alkyl aryl type non-ionic surfactant Triton X-100 (TX-100) in the presence of several 1-alkyl-3-methylimidazolium (Cnmim+) based non-amphiphilic, amphiphilic and biamphiphilic ionic liquids (ILs) varying in the alkyl chain length of the cation (C4–C10) and different anions viz. chloride [Cl−], tetrafluoroborate [BF4−], trifluoromethanesulfonate [CF3SO3−], hexaflurophosphate [PF6−] and octylsuphate [C8SO4−] have been systematically investigated by cloud point (CP), viscosity, dynamic light scattering (DLS), nuclear magnetic resonance (NMR), fluorescence and small-angle neutron scattering (SANS) measurements. These ILs interact with TX-100 micelles on account of their hydrophobicity; ILs with a hydrophilic counter ion (Cl−) favour demicellization, increase CP, decrease the solution viscosity and apparent hydrodynamic diameter (Dh) of micelle, whereas ILs with a hydrophobic counter ion (PF6−) increase the solution viscosity and exhibit micellar growth. SANS data on the size/shape of TX-100 micelles in the presence of different ILs are reported to provide information on microstructural changes in the micelles. The location of ILs, which has a dominating effect on the structure of the micelles, was evaluated using fluorescence and 1H NMR studies, and these results are discussed in terms of the insertion of the ILs in TX-100 micelles. IL molecules with long alkyl chains penetrate deeper in the TX-100 micelles. The present study provides useful information on tuning the solution characteristics of TX-100 in the presence of ILs that may have industrial applications.