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

Hypothesis: 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.

Experiments: 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.

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.