Exploring the interactions and aggregation of DTAB and SDS in choline-based ionic liquids: A combined experimental and computational study

In this work, the aggregation behavior of the cationic surfactant dodecyltrimethylammonium bromide (DTAB) and the anionic surfactant sodium dodecyl sulfate (SDS) were examined both in the presence and absence of 0.1 wt percent aqueous ionic liquids (ILs) solutions using conductivity, surface tension and steady-state fluorescence measurements. Four choline based ILs were used, such as choline dihydrogencitrate ([Ch][DiHCit]), choline acetate ([Ch][Ac]), choline chloride ([Ch][Cl]), as well as choline bitartrate ([Ch][Bit]). Experimental conductivity measurement was done at five different temperatures ranging from 283.15 K to 313.15 K. The addition of ILs significantly reduced the CMC values for both surfactants, with [Ch][DiHCit] lowering DTAB's CMC to 14.31 mM, and [Ch][Ac] being most effective for SDS, reducing its CMC to 4.31 mM. From the electrical conductivity measurements, various thermodynamic parameters such as critical micelle concentration (CMC), degree of ionization of the counterion on the micelles (alpha), standard free energy enthalpy (Delta H degrees m) and entropy. The findings showed that (Delta H degrees m) decreases linearly with temperature, shifting from positive to negative around room temperature. The surface adsorption parameters such as maximum surface excess concentration, minimum area per molecule, surface pressure at CMC, efficiency of adsorption and packing parameters were analyzed by means of plots of the surface tension as a function of the total surfactant concentration to understand the interfacial behavior of DTAB and SDS in IL/surfactant systems, highlighting the role of IL anions and cations. Further the DFT study was done to predict electrostatic, hydrophobic, and hydrogen-binding interactions.