Liquid Surfaces with Chaotic Capillary Waves Exhibit an Effective Surface Tension

The influence of chaotic capillary waves on the time-averaged shape of a liquid volume is studied experimentally and theoretically. In that context, a liquid film containing a stable hole is subjected to Faraday waves. The waves induce a shrinkage of the hole compared to the static film, which can be described using the Young-Laplace equation by incorporating an effective capillary length. In the regime of chaotic Faraday waves, the presented theoretical model explains the hole shrinkage quantitatively, linking the effective capillary length to the wave energy. The effect of chaotic Faraday waves can be interpreted as a dynamic surface force that acts against surface tension.