ИСТИНА

We investigate the changes in the tensile properties of air/ water interfaces in presence of a volatile surfactant, so that continuous evaporation is taking place simultaneously with the adsorption or desorption. The study is performed with linalool, benzyl acetate, and citronellol. The adsorption is quantified by measuring the kinetics of surface tension, σ(t); drop shape analysis was carried out, with sessile and pendant drops – σ(t) is found to increase (see Fig. 1). This dependence is explained in the frames of a proposed theoretical model, taking into account the balance of fluxes at the interface. The adsorbed amount [Γ(t)], the surface tension [σ(t)], and the sub-surface concentration [cs (t)] are connected by an equilibrium isotherm – it is determined separately, in absence of evaporation, by measurements using the Maximum Bubble Pressure Method. The data are fitted with the van der Waals equation of state. The obtained σ(cs ) dependence is combined with the mass transport kinetics, to yield a prediction for σ(t). We achieve good agreement between theory and experiment (Fig. 1). One adjustable parameter (material constant) is determined – the mass transfer coefficient of the volatile amphiphile (VA) across the A/W boundary. Results for different VA are presented.