Ionic liquid induced changes in the properties of aqueous zwitterionic surfactant solution

Area of Science:

• Physical Chemistry
• Supramolecular Chemistry
• Materials Science

Background:

• Modifying aqueous surfactant solution properties with additives is crucial.
• Ionic liquids (ILs) possess unique characteristics making them suitable additives.
• Zwitterionic surfactants like N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (SB-12) are widely studied.

Purpose of the Study:

• To investigate the impact of a hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), on the physicochemical properties of aqueous SB-12 surfactant solutions.
• To determine how [bmim][BF4] affects micellar size, critical micelle concentration (cmc), and aggregation number (Nagg).
• To explore changes in the micellar pseudophase's microenvironment, including dipolarity and microfluidity.

Main Methods:

• Dynamic light scattering (DLS) was employed to measure average micellar size.
• Fluorescence probe techniques were utilized to determine cmc, Nagg, and micellar pseudophase properties.
• Systematic variation of [bmim][BF4] concentration up to 30 wt% was performed.

Main Results:

• Dynamic light scattering revealed a significant reduction in average micellar size upon addition of [bmim][BF4].
• Increasing [bmim][BF4] concentration generally led to a decrease in Nagg and an increase in cmc.
• Fluorescence probe data indicated increased dipolarity and microfluidity within the micellar pseudophase, attributed to enhanced water penetration.

Conclusions:

• The ionic liquid [bmim][BF4] significantly alters the aggregation behavior and micellar properties of aqueous SB-12 surfactant solutions.
• [bmim][BF4] acts as an electrolyte/cosurfactant at low concentrations and a polar cosolvent at high concentrations.
• The observed changes are explained by electrostatic interactions and a reduction in hydrophobic effects due to the presence of the IL.