The micelle thermodynamics and mixed properties of sulfobetaine-type zwitterionic Gemini surfactant with nonionic and anionic surfactants

The surface tension curves of three zwitterionic Gemini surfactants (GCS12, GCS14, and GCS16) were measured at different temperatures. According to the values of critical micelle concentration (cmc) and γcmc, the thermodynamic parameters of these surfactants were calculated. As temperature increases, the cmc values decrease, and the surface activities increase. The thermodynamic parameters indicate that the micellization and adsorption of these surfactants are spontaneous, endothermic and entropy-driven. The process of micellization and adsorption features an enthalpy-entropy compensation phenomenon. The compensation temperatures of micellization are in the range of 311.2~312.8 K, while those of adsorption are between 310.2 K and 312.2 K. Among these surfactants, GCS14 aggregates most easily into micelles, and the micelles of GCS14 are the most stable. Moreover, the mixed properties of GCS14 with anionic surfactant (SDS) and nonionic surfactant (CDA) were investigated, respectively. The GCS14/SDS mixtures exhibit excellent surface activities, and GCS14 plays an essential role in the mixtures. At αGCS14 = 0.8, the cmc and γcmc values reach a minimum. According to the regular solution theory, the great absolute values of βσ (for mixed monolayer formation at the aqueous solution/air interface) and βm (for mixed micelle formation in aqueous solution) indicate the strong attraction between GCS14 and SDS. The GCS14/SDS mixtures show synergistic effects in three properties, including the efficiency in surface tension reduction, the ability of micelle formation, and the ability of surface tension reduction. Also, the mixtures of GCS14 and CDA feature excellent surface activities. At αGCS14 = 0.8, the cmc and γcmc values reach a minimum. For the GCS14/CDA mixtures, the great absolute values of βσ and βm suggest these mixtures exhibit the synergistic effect in the surface tension reduction and the formation of the micelles. Zwitterionic Gemini surfactant GCS14 reveals stronger synergistic effects in the formation of mixed micelle and mixed monolayers with anionic surfactant (SDS) than with the nonionic surfactant (CDA). The molecule attraction between GCS14 and SDS or CDA in the mixed films is stronger than in the micelles.