Interactions in binary mixtures of nonionic gemini-surfactants surfynol® 400 series with sodium lauryl sulfate. Micellization in the aqueous medium

Abstract

Adsorption at the water – air interface and micelle formation in water in binary mixtures of nonionic gemini surfactants Surfynol® 400 series with different degree of oxyethylation (30, 10, 3.5 and 1.3, respectively) and short rigid spacer with triple –C≡C– bond and anionic surfactant of sodium lauryl sulfate were investigated. Their critical micelle concentration (CMC) values were experimentally determined. CMC values of binary mixtures are lower than thats of either surfactant by itself which shows non-ideal behavior of surfactant molecules in micelles.The values of interaction parameters in mixed micelles βm were calculated using the Rubingh thermodynamic approach, the compositions of mixed micelles Xm were determined. The higher surface activity and the lower are the CMC values of the gemini surfactants Surfynol®, the higher are its part in the mixed micelles and the range of molar fraction of Surfynol® within which the mixed micelles is enriched with it.The negative values of the interaction parameters βm and the fulfillment of the condition |ln (C1m/C2m)| < |βm| submit synergism in mixed micelle formation in binary surfactants mixtures studied. The parameter value depends on the oxyethylation degree of nonionic surfactant. The reason is that the gemini surfactant’ oxyethyl chains interact with the sodium cation of sodium lauryl sulfate like crown ethers and transformation of the nonionic surfactant into the associated cationic one which is capable to electrostatic interaction with the anionic surfactant followed by molecules mutual attraction. It is also a fact that the gemini surfactants studied have a specific molecular structure. They have a short rigid spacer which sets a limit on the mutual disposition of the oxyethyl chains.