Liquid Pool Lift-Off and Sound

The impact and rebound of droplets from solid surfaces has important engineering applications including painting, fluid injection and printing.  To reduce the contact time with the surface, patterning and hydrophobic coatings have been used.  With these coatings, the wetting is reduced such that the drop rebounds similar to a spring.  However, residual liquid pools may still occur on treated surfaces.  Research by Dr. John Allen and international collaborators published in Communications Physics (December 22, 2022) highlights a novel method using hydrogel spheres to remove residual liquids such as oil and contaminants in emptied storage tanks  During a complete lift-off of the liquid pool, entrained air coalesce into collapsing air bubbles which produces a characteristic sound upon rebound.