Soluting effect of amino acids on 1‑decyl‑3‑methylimidazolium bromide and 1‑dodecyl‑3‑methylimidazolium bromide as cationic surfactants and sodium dodecyl sulfate as anionic surfactant in aqueous solutions

Abstract In this work, with the aim of shedding light on the effect of zwitterion cosolutes (amino acids) on the aggregation and surface behaviors of both cationic and anionic surfactants in aqueous solution, surface and micellar behavior of 1‑decyl‑3‑methyl imidazolium bromide ([C 10 mim]Br), 1‑dodecyl‑3‑methyl imidazolium bromide ([C 12 mim]Br) and sodium dodecyl sulfate (SDS) in aqueous solutions of 0.7 mol·kg −1 glycine, alanine and proline were studied by means of volumetric, compression, electric conductivity and surface tension measurements at different temperatures. From the experimental density and speed of sound data, the various parameters such as apparent molar volume, isentropic compression, apparent molar isentropic compression and the change of apparent molar volume upon micellization as well as upon transfer from pure water to aqueous amino acid solutions were derived. Our results showed that the order of isentropic compression for the investigated surfactants in presence of the amino acids was: SDS > [C 12 mim]Br ≫ [C 10 mim]Br. Also the obtained negative values for transfer apparent molar volume from pure water to aqueous amino acid solutions in ternary systems of ([C 10 mim]Br + water + proline) and ([C 12 mim]Br/SDS + water + glycine/alanine/proline) indicated that hydrophobic-hydrophobic interactions are predominant. The values of the degree of ionization of the counter ion on the micelles and thermodynamic properties of micellization for the investigated surfactants in aqueous amino acids solutions were obtained from the electrical conductivity measurements. It was found that, hydrophobic-hydrophobic interactions between the aliphatic chain of surfactants and amino acids have unfavorable effects on micelle formation. From the surface tension measurements, a series of parameters, including adsorption efficiency, surface tension at CMC, surface tension at micellar phase (γ mic ), effectiveness for surface tension reduction, maximum surface excess concentration and minimum surface area per molecule were determined for the investigated surfactants in the presence of different amino acids at 298.15 K. All the investigated amino acids have soluting-out effect and their abilities to reduce the CMC of the surfactants in aqueous solutions decrease with an increase in the hydrophobicity of the amino acid. Resultant data showed that the ability of the amino acids to decrease the CMC followed the order: glycine > alanine ≫ proline.