In the current work, we discuss the mixed micelles and thermodynamic micellization of aqueous binary mixture of polyoxyethylene - 20 sorbitan-monododecanoate (Tween 20) as nonionic surfactant and Benzyldimethylhexadecyl ammonium chloride (HDBAC) as cationic surfactant using conductivity and surface tension (γ) estimations in the temperatures range (288 -318K). Critical micelle concentration (CMC) and variables of micellization, like the standard thermodynamic functions: Gibbs free energy (Δ𝐺𝑚 ⁰ ), enthalpyΔ𝐻𝑚 ⁰ ) and entropy (Δ𝑆𝑚 ⁰ ) were calculated using the variation of conductivity and γ with molar concentration and the variation of ln XCMC with temperature. The experimental CMC values were applied to calculate the mole fractions of surfactant in the mixed micelle (𝑋1 𝑚 ), the β parameter and the coefficient of activity f1and f2, using the equations proposed by Clint and Rubingh, which indicate the β parameter, is always negative. In addition, the results of thermodynamic parameters show that ΔG⁰m are negative for both individual and mixture of HDBAC-Tween20 surfactants and the values negatively increased with increasing temperature while its negative values decreasing with decreasing initial mole fraction of HDBAC.
