Surface activity of sodium dodecylsulfate at the interface «solution based on a deep eutectic solvent/air»

Surface activity of sodium dodecylsulfate and micelle formation in solutions based on deep eutectic solvents ethaline and reline (eutectic mixtures of choline chloride with ethylene glycol and urea, respectively) were investigated. The isotherms of surface tension were treated using Langmuir model and the adsorption parameters at the interface «solution/air» were determined. The change in the nature of a solvent results in a decrease in the adsorption equilibrium constant in the following sequence: water>reline>ethaline>ethylene glycol, which is caused by the corresponding changes in the solvents polarity and intensity of hydrophobic interactions. The critical micelle concentration of sodium dodecylsulfate is equal to 3.55‧10^-3 Ì and 2.14‧10^-3 Ì in solutions based on ethaline and reline, respectively. These values are lower than that in an aqueous medium (8.11‧10^-3 Ì). An increase in the content of water additive in deep eutectic solvents has only a marginal impact on the adsorption equilibrium constant, but leads to an increase in the critical micelle concentration.