Dynamic Surface Tensions of Fluorous Surfactant Solutions

Dynamic surface properties of aqueous solutions of cationic fluorous surfactant CF3CF2CF20(CF(CF3)CF2O)2CF(CF3)CONH(CHE)3N^+(C2H5)2CH3I^- (abbrev. FC-4 ) were reported. The critical micelle concentration (cmc)(3.6×10^-5 mol/L) and equilibdum surface tensions γeq were measured by Krtlss K12 tension apparatus. Dynamic surface tension γ(t) was measured in the range of 15 ms to 200 s using the MBP tensiometer. The surface excess Γ,as a function of concentration, was obtained from equilibrium tensiometry using the Gibbs equation. Data from these experiments were combined to analyze the γ（t) decays according to the asymptotic Ward and Tordai equation.The results show that at the initial adsorption stage, the dynamic surface tension data were all consistent with this diffusion-controlled mechanism, and at the end of the adsorption process, there were some evidences for an adsorption barrier, suggesting a mixed diffusion-controlled adsorption mechanism. Using measured quantities, the barrier strength was estimated as between 25 and 35 kJ/mol at 25℃. The surface pressure plays an important role in contributing to the barrier.