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

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) zeta 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 0.10 M, 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 0.15 M, 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. (C) 2016 Elsevier B.V. All rights reserved.