Adsorption kinetics of 1-dodecanol at an air-water interface

The adsorbed monolayer of the soluble surfactant 1-dodecanol at the air-water interface has been demonstrated to have two phase transitions, G-LE and LE-LC [6]. Two constant surface tension regions were observed in the dynamic surface tension γ(t) profiles at 20°C and both the generalized Frumkin (GF) model and the phase transition (PT) model described well the equilibrium surface tension, γ(C). In this work, we examined whether the GF or PT model could describe the adsorption kinetics of 1-dodecanol onto a freshly created air-water interface. The equilibrium and dynamic surface tension data (γ(C) and γ(t) for γ>55mN/m as reported by Tsay et al. [6]) were used for this examination. It was concluded that (i) the classic Frumkin model describes poorly both the γ(C) and γ(t) behavior; (ii) although the GF model predicts well the γ(C) data, it predicts γ(t) profiles poorly; (iii) the PT model describes both γ(C) and γ(t) well; and (iv) the adsorption of 1-dodecanol onto a clean air-water interface is controlled by diffusion. An average diffusivity of (8.1±2.6)×10^-6cm²/s resulted from the fit between the phase transition model and the γ(t) data.