Laboratory Study of Surfactant Film Compression and Boundary Transformation under the Action of Surface Waves

Abstract

In this paper we present the results of a laboratory experiment simulating the mechanisms of a surfactant film localization under the action of periodic surface waves. It is shown that the film compressed by a surface wave, can be conditionally divided into three sections — the dense film region as the most distant from the wave source, the area of a diluted film and the region of relatively clean water. The paper is focused on the processes occurring in the diluted film region characterized by the transition from clean water to the dense film, where horizontal circulation currents are registered. The character of currents is varying depending on the wave amplitude so that the divergent circulation cells occur at small and large wave amplitudes, but at medium amplitudes the roller currents forming a convergence zone on the basin axis are observed. The experimentally obtained stationary distribution of surfactant concentration is compared with the previously developed model of film compression due to surface tension induced by waves. The comparison shows good agreement between the theory and the experimental results at small and large wave amplitudes. Their discrepancy at medium wave amplitudes in the diluted film region is presumably related to the presence of convergent cells which are not considered in the model.