Surfactant-laden bubble dynamics under porous polymer films.

The dynamics of air bubbles spreading on the underside of solid substrates is an important scientific problem with numerous applications. This work explores the spreading of bubbles against an ultra-thin, porous ultra-high-molecular-weight polyethylene (UHMWPE) film. This polymer film can be used in applications where a solid-liquid-gas interface is involved, like froth flotation for mineral processing, underwater methane capture, to prevent foaming in bioreactors, and in degassing in microfluidics. When an air bubble is released underneath such a film, the bubble bounces against the film, makes contact after the liquid film dewets, spreads against the film and shrinks in size as the gas within the bubble permeates through the pores of the film. In our work, these events were recorded using a high-speed camera. The effect of different surface-active species like surfactants, which exhibit interfacial mobility and proteins, which form a viscoelastic interfacial network, was also studied. The adsorption of these surface-active molecules led to profound differences in the interaction of the bubbles and their ultimate removal through the film. Importantly, the permeation flux of the bubbles was lower in the presence of these molecules, affected in part by a lower capillary driving force and also because of the decreased film permeability. This ultra-thin film offers a high permeation flux, which makes it a promising candidate for the aforementioned applications. Furthermore, the effect of surface-active species such as surfactants and proteins encountered in these environments is elucidated.