Complex formation between cationic gemini surfactant and sodium carboxymethylcellulose in the absence and presence of organic salt

Abstract

Complex formation between cationic gemini surfactant 12-6-12 and anionic polyelectrolyte sodium carboxymethylcellulose (NaCMC) has been investigated in the absence and presence of organic salt sodium benzoate (NaBz) by turbidity, conductivity, isothermal titration microcalorimetry (ITC), ζ potential, light microscopy and SEM measurements. In the absence of salt, the NaCMC/12-6-12 system experiences the aggregate transitions from fibrous structure of the polymer NaCMC to soluble beaded structured NaCMC/12-6-12 aggregates and then to precipitated networklike cross-linked structured NaCMC/12-6-12 aggregates with increasing 12-6-12 concentration. The addition of salt is found to markedly influence the formation of NaCMC/12-6-12 complexes. When the NaBz concnetration is less than or equal to 0.10M, the phase behavior of the NaCMC/12-6-12/NaBz system is similar to that of NaCMC/12-6-12 in the absence of salt, but the lower 12-6-12 concentration is needed for the formation of precipitation. When the NaBz concnetration is greater than or equal to 0.15M, the phase behavior include no NaCMC/12-6-12/NaBz complex formation, soluble long and dense threadlike micelles, coacervate with a structure of the three-dimensional connected network by entanglement of threadlike micelles, and precipitate with a structure of mat by entanglement of threadlike micelles with increasing 12-6-12 concentration. The salt effect on NaCMC/12-6-12 complex formation is mainly explained as the result of the salt on the gemini surfactant 12-6-12. However, the presence of polymer significantly enlarges the limits of coacervation, especially at higher salt concentration.