Study on Interaction of Carboxylic Acid Gemini Surfactant with Cocamidopropyl Betaine in Aqueous Solution

The interaction of carboxylic acid gemini surfactant 4,8-didodecyl-3,9-dioxo-6-hydroxy-4,8-diaza-1,11-undecanedicarboxylic acid (CGS12) with amphoteric surfactant cocamidopropyl betaine (CAPB) at 25 degrees C and pH 7.0 has been investigated using pH titration, surface tension, dynamic light scattering (DLS) and cryogenic transmission electron microscopy (Cryo-TEM) measurements. The pH titration results show that CGS12 exhibits anionic surfactant properties and CAPB exists as a zwitterionic form at pH 7.0. The surface tension results show that the critical micelle concentration (CMC) values of the CAPB/CGS12 mixture are low, and basically exhibit a decreasing trend with decreasing molar ratio of CAPB (X-CAPB). The variation of the CMC of the mixture reveals that the mixing is close to ideal. The DLS results indicate that the CAPB/CGS12 mixture mainly forms the larger aggregates with the hydrate radii approximately 70-145 nm at various X-CAPB. The Cryo-TEM images further demonstrate the CAPB/CGS12 mixtures mainly form vesicles. The results indicate that the aggregate size and microstructure of the mixture change little with the variation of X-CAPB.