Auto-oscillation of surface tension: heptanol in water and water/ethanol systems

The dynamic processes which occur as a result of dissolution of a surfactant droplet under the air/solution interface are affected by the presence of a limited (heptanol) and an unlimited (ethanol) soluble surfactant in the aqueous immersion medium. In the considered system, the dissolution of a heptanol droplet causes auto-oscillations of the surface tension, as previously observed at dissolution in pure water. It is demonstrated by the experimental results that the oscillations characteristics are strongly influenced by the composition of the immersion medium. The experimental data are discussed and compared with the results of numerical simulation of the behaviour of a model system with a heptanol droplet immersed in an aqueous heptanol solution. Good qualitative agreement between theory and experiment is shown.