Abstract: By using drop-volume method, the surface tension of disodium hexadecyl diphenyl ether disulfonate (C₁₆-MADS) was measured in different NaCl concentrations (0～0.50 mol•L^-1 NaCl) at different temperatures (298.0～318.0 K). The results show that with the increase of temperature, the critical micelle concentration (cmc) of C₁₆-MADS slightly increases, but the maximum surface excess concentration at the air/water interface (Γ_∞) decreases. The cmc of C₁₆-MADS decreases from 1.45×10^-4 mol•L^-1 down to 4.10×10^-5 mol•L^-1 as the concentration of NaCl increases from 0 to 0.50 mol•L^-1, but the corresponding surface tension at the concentration (γ_cmc) shows no variation. As the increase of NaCl concentration, Γ_∞ of C₁₆-MADS increases as the increase of temperature in the range of 298.0～303.0 K, but abnormally decreases from 2.27 μmol•m^-2 down to 1.41 μmol•m^-2 in the range of 308.0～318.0 K. The micellization free energies (ΔG_m⁰) are in the range －63.98～－76.20 kJ•mol^-1 in the studied ranges of temperature and NaCl concentration. The process of micellization of C₁₆-MADS in aqueous solution is mainly driven by the entropy.

Key words: Disodium hexadecyl diphenyl ether disulfonate, Surface tension, Critical micelle concentration