Vanillin based cationic surfactants mixed systems: Micellization and interfacial interaction behaviors in presence of nonionic conventional surfactant

• Mixing of cationic and nonionic improves surface activity.
• Large contribution of cationics in micellar form was observed than the expected.
• Synergistic interaction appeared for the mixed micelles due to negative βm.
• Low ΔGex values indicated the stability of the formed mixed micelles.

The micellization and interfacial interaction behaviors of two cationic vanillin-based surfactants in presence of cetyl dimethyl phosphinate (CDP) were investigated at various molar ratios. Surface tension measurements were used to obtain the critical micelle concentration (CMC) values of the studied surfactants, these CMC values were obtained as functions of the composition. The mixed systems data were analyzed according to the regular solution model developed by Rubingh for mixed micelles. Two interaction parameters were obtained for each system, the interaction at the interface, and in the micellar phase. The properties of the mixed systems at interface and in bulk of the solutions were correlated to the individual surface properties of each surfactant. Results showed that the chemical structure and initial molar ratio of the cationic surfactants in the mixed systems affect their partitioning in the mixed micelles and adsorbed mixed monolayers. Negative interaction parameters of the systems in the bulk (mixed micelles) and at the interface (mixed adsorbed monolayer) indicate the synergism of the mixing process.

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