Thermodynamic Insights into Micellization of Surfactant Tetradecyltrimethylammonium Bromide in Aqueous Choline-Based Ionic Liquid Systems

Abstract

Adjusting surfactant behavior in aqueous solutions is a key factor in optimizing their performance by introducing biocompatible ionic liquids (ILs) to the solvent system. In this study, thermodynamic properties of tetradecyltrimethylammonium bromide (TTAB) in water and in 0.1 wt % IL/water systems of four different choline-based ILs─choline dihydrogencitrate [Ch][DiHCit], choline acetate [Ch][Ac], choline chloride [Ch][Cl], and choline bitartrate [Ch][Bit], have been explored, as ILs at this low concentration act as electrolytes which increases the polarity of the solvent that improves the micellization behavior of the TTAB. A combination of conductivity, surface tension, and fluorescence-based measurements was applied to examine the micelle formation attributes and interfacial properties. Temperature-dependent conductivity measurements at a temperature range of 283.15–313.15 K were conducted to calculate the thermodynamic parameters of micellization (ΔG_m^°, ΔH_m^°, ΔS_m^°), where ΔG_m^° was found to be negative in all IL/water systems which improves the spontaneity of micelle formation. The interfacial properties including surface excess concentration (Γ_max), minimum area per surfactant monomer (A_min), surface pressure at CMC (π_cmc), and interfacial adsorption efficiency (pC₂₀) were calculated using surface tension results to predict the interfacial behavior of the TTAB. The Debye screening length (χ^–1) of the solutions and static dielectric permittivity (ε) were also measured.