Solutal Marangoni stresses delay Rayleigh-Taylor instability*

Understanding the Rayleigh-Taylor instability of volatile liquid films is crucial in widespread applications like coating, wetting and painting to prevent liquid droplets from falling. To date, the thermal effects have been mainly considered for the instability of volatile liquid films, including binary mixtures, while the solutal Marangoni effects were ignored because the major assumption was the very thin film thickness and small Peclet number. In this study, we explored how the instability of the suspended binary mixture thin film under a ceiling was influenced by the solutal Marangoni effect through both numerical and experimental investigations. Here, we systematically controlled a dimensionless Marangoni number to investigate its stability. We derived simplified long-wave evolution equations for the gas-liquid interface, and performed a linear stability analysis. Furthermore, we performed a deflectometry experiments that showed that the binary mixture thin film was more unstable when the surface tension of the more volatile component was higher than that of the other component. Conversely, when the surface tension of the more volatile component was lower, the instability was either stabilized or exhibited an oscillatory mode, which delayed the exponential increase in amplitude. As a result, we propose that binary mixtures where the volatile component has lower surface tension are more effective at preventing liquid droplet falling by delaying the exponential growth of film thickness.