Aggregation behavior of mixed systems of imidazolium-based ionic liquid and sodium octanesulfonate
Two mixed systems consisting of an anionic surfactant and a cationic surface-active ionic liquid were studied.The mixture of sodium octanesulfonate(SOS)and 1-decyl-3-methylimidazolium bromide([C10mim]Br),and the mixture of SOS and 1-tetradecyl-3-methylimidazolium bromide([C14mim]Br),were both investigated using surface tension measurement.The parameters,such as critical micelle concentration(cmc),surface tension at cmc(γcmc),surface pressure at cmc(Πcmc),maximum surface excess(Γmax)and minimum area per molecule(Amin),were obtained.The mixed micellar parameters including micellar mole fraction(X1m),micellar interaction parameters(βm)and activity coefficients(f1m and f2m)were calculated by applying Rubingh's regular solution theory.The calculated parameters confirmed that there were strong synergy in all these mixed systems,and the interaction of SOS with[C14mim]Br was stronger than that with[C10mim]Br.Thermodynamic parameters for mixed monolayers and mixed micelles were calculated and discussed,which indicated that the mixed micelles were spontaneously formed and were thermodynamically stable systems.Turbidity measurement was conducted using spectrophotometry.The phase diagrams were plotted for each system based on visual observations and absorbance values.The mixed systems of SOS/[C10mim]Br and SOS/[C14mim]Br all exhibited three concentration regions:a low-concentration homogeneous solution region,a two-phase region,and a high-concentration homogeneous solution region.
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