(144f) Bubble Spreading on Porous, Aerophilic Polymer Films

The spreading of water droplets on hydrophilic and hydrophobic solid substrates is a well-studied problem. The analogous problem of an air bubble spreading on the underside of an immersed substrate is not well understood. This work explores the spreading of bubbles against an ultra-high-molecular-weight polyethylene (UHMWPE) film, which is porous and hydrophobic (aerophilic). This can be used to prevent foaming in applications where a solid-liquid-gas interface is involved, like froth flotation for mineral processing, carbon dioxide/methane capture, and this film can be used as a foam prevention lid in bio-reactors for cell culture. When an air bubble is released underneath this film floating on water, the bubble rises up, bounces against the film, spreads and eventually shrinks in size as the gases within the bubble diffuse out through the pores. These events were recorded using a high-speed camera and the radius of the bubble and the radius of spread onto the film were monitored. Interestingly, after the bubble reached its maximum spread area on the film, the three-phase contact line of the bubble was pinned, with a constant spread radius, as the bubble shrunk and diffused out. The effect of different surface-active species like proteins and surfactants present in the solution, more relevant to aforementioned applications, was also studied. With these species adsorbed onto the bubble and the film surface, the bubbles spread less and diffused out slower. It is important to decouple the effect of these proteins/surfactants in modifying the polymer film properties (like membrane stiffness) and in affecting the rising bubble's dynamics (like deformation prior to impact). Towards this, the kinetics of interfacial adsorption onto the bubble and the film were studied by controlling the adsorption state of the dynamic adsorption layer as the bubble is released and rises up onto the film.