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].