Effect of hydrophilic ionic liquid on the micellar properties of aqueous Tween-20

• The effect of addition of IL on the aggregation behavior of nonionic surfactant has been investigated using fluorescence probe behavior studies and dynamic light scattering.
• The data strongly suggests the partitioning of [C5mim][BF4] into the micellar phase of Tween-20.
• The addition of IL resulted in an increased cmc, decreased Nagg and micellar size.

The micellar behavior of a nonionic surfactant, polyoxyethylene (20) sorbitan monolaurate (Tween-20) in different wt% of a hydrophilic ionic liquid, 3-methyl-1-pentylimidazolium tetrafluoroborate ([C5mim][BF4]) was investigated using techniques like fluoremetry and dynamic light scattering. Two fluorescence probes viz. pyrene and pyrene-1-carboxaldehyde were utilized. The critical micelle concentration (cmc) of Tween-20 was found to increase with increasing amount of [C5mim][BF4]. The significant increase in cmc and decrease in aggregation number (Nagg) indicates an “unfavorable” micellization within aqueous Tween-20 solution when [C5mim][BF4] is present. The increase in dipolarity upon [C5mim][BF4] addition suggests increased water penetration due to the presence of [C5mim][BF4] in the micellar pseudophase. Dynamic light scattering studies provide the evidence of micelle-like aggregates even in the presence of 2 wt% [C5mim][BF4].