Drainage and lifetime of thin liquid films: the role of salinity and convective evaporation

TL;DR

This study experimentally examines how salinity and atmospheric humidity influence the drainage and lifetime of thin liquid films, revealing humidity's dominant role and deriving scaling laws for film lifetime based on evaporation rates.

Contribution

The paper introduces new experimental insights into the effects of salinity and humidity on film drainage and lifetime, including the derivation of scaling laws for evaporation-driven lifetime changes.

Findings

Film drainage is unaffected by humidity but depends on viscosity changes due to salinity.

Film lifetime increases significantly with humidity, from seconds to minutes.

Air mixing reduces average film lifetime and alters its distribution.

Abstract

We experimentally investigate the effect of salinity and atmospheric humidity on the drainage and lifetime of thin liquid films motivated by conditions relevant to air-sea exchanges. We show that the drainage is independent of humidity and that the effect of a change in salinity is only reflected through the associated change in viscosity. On the other hand, film lifetime displays a strong dependence on humidity, with more than a tenfold increase between low and high humidities: from a few seconds to tens of minutes. Mixing the air surrounding the film also has a very important effect on lifetime, modifying its distribution and reducing the mean lifetime of the film. From estimations of the evaporation rate, we are able to derive scaling laws that describe well the evolution of lifetime with a change of humidity. Observations of the black film, close to the top where the film ruptures, reveal that this region is very sensitive to local humidity conditions.