We discuss a procedure for interpretation of experimental results for dynamic interfacial tension, at O/W or A/W boundaries. Based on a previous theory [T. Gurkov, Colloid Polym. Sci. 289 (2011) 1905], data points for the surface pressure Π, measured vs. time and at different surfactant concentrations, can be represented in the form of a "master curve". The latter is fitted with an appropriate surface equation of state, which takes into account the lateral interactions and the sizes of surfactant and solvent molecules [T. Gurkov et al., Colloids Surf. A 87 (1994) 81]. This method is applicable at Π smaller than about 18, 14, or 9 mN/m - depending on the system. The good agreement between theory and experiment allows one to quantify the adsorbed amount per unit area, and its time evolution, Γ(t). The interaction parameter (β) in the equation of state is also determined. For the anionic surfactant Na-laurate at A/W interface, the electrostatic contribution to Π is included; the results for Γ(t) reveal a barrier mechanism for adsorption, with the characteristic time of ~150 min. In addition, β=6.5, which indicates a significant lateral attraction. The cationic surfactant cetyl trimethylammonium bromide on hexadecane/ water boundary, in the presence of salt, shows β=0 and diffusion-controlled adsorption, possibly affected by pre-micellar aggregates. For the non-ionic surfactant C10EO4 at A/W, the analysis of literature data demonstrates purely diffusional mechanism of adsorption. Interesting is the fact that β=-8.9; the observed repulsion of considerable magnitude is probably due to the extending polar headgroups. Our calculations can be useful for analysis of measured data for adsorption dynamics in undersaturated surfactant layers (at degree of coverage below ~0.5-0.6).
tg@dce.uni-sofia.bg
