Probing The Essence Of The Performance Improvement In Mixing Surfactants And Deducing The Mixing Rule Of Ionic/Nonionic Surfactant Mixtures Of Best Performance Using~1H-NMR

Critical micelle concentration(CMC)is an important physicochemical property of surfactants because it is a signal that micelles start to form,and surfactants take on characteristics of detergency,moist,emulsification and solubilization.Surfactant mixtures with proper additives can make CMCs decrease and improve the performances.So,it is meaningful to explore the mixing rule of surfactant mixtures for better performance.The classical theory of Synergistic effect in mixed surfactants is inaccurate for it is based on "the CMC of the mixed surfactant solution",however,each component in the mixture exhibits its own separately behavior.Nuclear magnetic resonance(NMR)spectroscopy has some advantages of not only providing information at micro level but also giving a chance to observe separately behaviors of each individual surfactant in the mixtures at the same time,without disturbing the sample.In this work,we applied 1H-NMR method to measure the CMCs of a series of surfactants in the mixed state,probing the essence and affecting factors of the synergy in mixing two surfactants,and did some experiments on more complex ternary surfactant systems.The results are listed as follow:1.The essence of the synergism in mixtures of two surfactants:In dilute solutions of surfactants,the concentration of the first surfactant adsorbed on the interface will be decreased if a second one is added.It is also true for the second surfactant.According to the adsor:ption equilibrium,the concentrations of the corresponding surfactants in the solution phase should be lower than that of the single surfactant state,so the excess molecules in the bulk solution are caused to aggregate forming micelles.And the result is that mixed surfactants aggregate forming micelles in a concentration lower than their CMCs.2.Electrostatic interaction is the main affecting factor of the synergism in mixing two surfactants,two mixed surfactants of similarly charged show greater synergic effect than that of oppositely charged ones.Steric effect also play an important role,both hydrophobic length and hydrophilic size can have influence on synergy.3.When the proportion of cationic and anionic surfactants is dramatic,the interaction between them could first happened,and the ternary system’s behavior is just alike the binary one that nonionic surfactant in mixing with the excessive ion,and the effect on nonionic component is little.If there is a great difference between the cross sectional area of cationic and anionic surfactants,the one with smaller cross sectional area will be more easily influenced.