Soap Film Drainage Using a Centrifugal Thin Film Balance

TL;DR

This study explores soap film drainage and stability under varying gravity conditions using a centrifugal thin-film balance, revealing the dominant drainage mechanisms and effects of gravity on film dynamics.

Contribution

It introduces a novel experimental setup to analyze soap film drainage under extreme gravity, demonstrating the robustness of marginal regeneration and capillary-driven drainage mechanisms.

Findings

Drainage governed by capillary suction and marginal regeneration.

Effective gravity influences film stretching, meniscus size, and TFE dynamics.

Measured thinning rates follow predicted scaling laws.

Abstract

Surface bubbles are an abundant source of aerosols, with important implications for climate processes. In this context, we investigate the stability and thinning dynamics of soap films under effective gravity fields. Experiments are performed using a centrifugal thin-film balance capable of generating accelerations from 0.2 up to 100 times standard gravity, combined with thin-film interferometry to obtain time-resolved thickness maps. Across all experimental conditions, the drainage dynamics are shown to be governed by capillary suction and marginal regeneration-a mechanism in which thick regions of the film are continuously replaced by thin film elements (TFEs) formed at the meniscus. We consistently recover a thickness ratio of 0.8-0.9 between the TFEs and the adjacent film, in agreement with previous observations under standard gravity. The measured thinning rates also follow the predicted scaling laws. We identified that effective gravity has three distinct effects: (i) it induces a strong stretching of the initial film, extending well beyond the linear-elastic regime; (ii) it controls the meniscus size, and thereby the amplitude of the capillary suction and the drainage rate; and (iii) it reveals an inertia-to-viscous transition in the motion of TFEs within the film. These results are supported by theoretical modeling and highlight the robustness of marginal regeneration and capillary-driven drainage under extreme gravity conditions.