Surface properties, micellar molecular interaction, and physical properties for binary systems of sodium oleate with three anionic surfactants

AbstractThe mixed micellization of the anionic surfactant sodium oleate (NaOL) and three anionic surfactants (NaDC, AOT, SDS) of different structures in 0.01 mol/L NaCl solution were investigated by surface tension measurement at different temperatures. All the investigated mixtures exhibited nonideal behaviors as the experimental CMC values are less than the CMC12ideal values calculated by using of Clint's equation. Negative βm values calculated by using of Rubingh's equation and |ln(CMC1/CMC2)| < |βm| proved synergism in the three systems of higher αNaOL or lower αNaOL. An interesting phenomenon of double inflection points were observed for pure NaOL and mixtures of high αNaOL. The negative ΔGm0 values for the mixed systems imply that the micelle formations are spontaneous process. The NaOL/NaDC system was also studied in buffer solution (pH 8, 12) at 30°C which also exhibited nonideal behavior. Synergism existed at pH 12 but not at pH 8 for NaOL/NaDC system. It is noteworthy that there were not double ...