As a class of novel surfactants, Gemini surfactants usually exhibit fairly excellent interfacial properties in aqueous solutions on account of the unique structure. They have significant application and development potential for industrial production. However, the mixing properties of Gemini surfactants with conventional surfactants are the key to their application. The equilibrium surface tension curves of anionic/nonionic surfactant mixtures based on the sulfonate Gemini surfactant (SGS‐12) were measured using the Wilhelmy Plate method. The parameters of surface adsorption, the interaction parameters between anionic and nonionic surfactants, and the thermodynamic parameters of micelle formation were calculated from the corresponding equations. In addition, the dynamic surface tension (DST) curves of anionic/nonionic surfactant mixtures were examined through bubble profile analysis, and the diffusion performance parameters were acquired from empirical formulas. The solubilization of pyrene in micelle solutions was studied using UV–vis absorption spectroscopy. The results show that the interaction parameters of all anionic/nonionic surfactants are negative, indicating that there is a synergistic effect on reducing the surface tension. For the SGS‐12/OP‐10, SGS‐12/Tween 80, SGS‐12/AEO9, and SGS‐12/APG0810 mixtures, the optimum mixing ratios are 6:4, 7:3, 7:3, and 8:2, respectively. The thermodynamic data of micelles show that the formation of mixed micelles for SGS‐12/APG0810 mixtures is an enthalpy‐driven process. The tendency of DST curves of the SGS‐12/APG0810 mixture is similar to that of SGS‐12. In comparison with single‐surfactant solutions, the anionic/nonionic surfactant mixtures show stronger solubilization capacity toward pyrene.
The interaction mechanism of multiple quaternary ammonium salts (MQAS) with bovine serum albumin (BSA) was examined by the fluorescence quenching method and circular dichroism (CD) spectra. Moreover, the effects of MQAS on the dynamic properties of BSA adsorption layers at different pH values were investigated using dilational interfacial rheology. Results show that the quenching constants increase with an increase in pH values and decrease with an increase in the experiment temperature at pH 5.3. The quenching mechanism is static quenching, and the electrostatic force dominates the interaction between MQAS and BSA at pH 5.3. Due to three positive head groups, MQAS can significantly affect the dynamic interfacial activity of BSA molecules at a relatively low concentration. At pH 4.3, the electrostatic repulsion is unfavorable for the formation of MQAS/BSA complexes. Consequently, MQAS molecules will replace BSA molecules from the interface by competitive adsorption. At the pH value above the isoelectric point of BSA, the electrostatic attraction is better for the formation of MQAS/BSA complexes, which exhibit a rapid adsorption rate and an enhanced interfacial activity. Moreover, the kinetic dependencies of interfacial dilational elasticity for the MQAS/BSA mixtures become nonmonotonous. The appearance of the maximum interfacial elasticity values can be attributed to the formation of tails and loops, which suggests that the addition of MQAS destroys the secondary and tertiary structure of protein in the bulk phase. In addition, the effects of MQAS on the secondary structure of protein were demonstrated by CD spectra.
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