Synergistic Effect Of Cocamidopropyl Betaine And Sodium Lauroyl Sarcosinate

Surfactant mixtures can spontaneously form various ordered aggregates in the solvent,which may lead better surface activity than single surfactant due to synergistic effect.Thus surfactant combination has important applications in pharmaceuticals,oilfield fracturing,household detergents.In this study,the surface activity,rheological properties and the interaction with proteins of zwitterionic surfactant（cocamidopropyl betaine,CAPB）,amino acid surfactant（sodium lauroyl sarcosinate,SLS）,and their mixed systems were investigated.First,the critical micelle concentration（CMC）,surface activity parameters and thermodynamic parameters of CAPB,SLS and CAPB/SLS mixed systems were determined by surface tension method.The results prove that the mixed systems have better surface activity and the lowest CMC is 0.134 mmol·L^-1.The interaction parameters were calculated to evaluate the synergistic effect between CAPB and SLS.The size and morphology of aggregation were characterized by dynamic light scattering（DLS）and transmission electron microscopy（TEM）,and the formation of 200–300nm wormlike micelles was observed.The foam properties of the mixed systems were also measured.Then,stable and dynamic viscoelastic measurements of the CAPB/SLS system were obtained.The surfactant mixtures with viscoelasticity exhibited typical non-Newtonian fluid behavior.The rheological results showed that wormlike micelles were formed and the effects of mole ratio,pH,temperature and concentration on the rheological properties of micelles were further investigated.The results indicate that the strongest wormlike structure formed under the condition of X₁=0.5,pH=4.7,and C_T=600 mmol·L^-1.Last,the polarity of the microenvironment of CAPB,SLS and CAPB/SLS were determined by steady-state fluorescence technique using pyrene as the probe.The solubility of stearic acid with surfactants was measured by UV-visible absorption spectroscopy.The fluorescence quenching of surfactants with BSA was studied by fluorescence method.The fluorescence intensity of BSA decreased and a blue shift was observed in the maximum emission peak with addition of surfactants.In addition,the synchronous fluorescence results revealed the conformational change of BSA.This work provides necessary guidance for the development of the formulations and rheological properties of amino acid-based cleaning products,as well as the irritating evaluation of surfactants at the protein level.It is of great significance for cosmetic,biological,pharmaceutical and other fields.