Morphological dynamics of thin liquid films formed by bubbles oscillating near a free surface: Experimental and...

Bubbles oscillating near a free surface are common across numerous systems. Thin liquid films (TLFs) formed between an oscillating bubble and a free surface can exhibit distinct morphological features influenced by interfacial properties, evaporation, and deformation history. We hypothesize that a continuous film presence throughout oscillation results in a wimple morphology, whereas intermittent film presence leads to a dimple formation. Additionally, we propose that the thickness of a wimpled film depends solely on the capillary number Ca, whether the bubble oscillates toward and away from the free surface or is pressed against it in two consecutive motions.

Using dynamic film interferometry, we investigate the morphology and drainage of TLFs formed with BSA and SDS surfactants. Controlled bubble oscillations allow us to test various deformation histories, and a lubrication theory-based model aids in interpreting the experimental findings.

Experiments confirm that film morphology is heavily influenced by deformation history, with continuous film presence throughout the entire deformation process leading to wimple formation. A modified lubrication-theory-based scaling captures the universal behavior of film thickness as a function of the capillary number across different morphologies. Our model aligns well with observed transitions between wimple and dimple shapes, offering valuable insights for the design of nanostructured surfaces.