Experimental investigations of air-cavity formation in viscous and viscoelastic liquids

This study delves into the phenomenon of air cavity formation resulting from sphere-liquid impacts, a subject of enduring scientific interest with broad interdisciplinary applications. The actual cavity and air bubble volumes following cavity rupture are for the first time measured and analyzed, in correlation with the thinning of the air filament. Utilizing direct visualization and an original image processing technique, we introduce a method for these precise measurements. We have explored the dynamics of this phenomenon across various fluids, including sunflower oil, glycerin, and polyethylene oxide (PEO) viscoelastic solutions. Impact velocity and fluid properties dictate not only the topology of the air cavity but also the volume dynamics and the evolution of the air thread near cavity rupture. Experiments with PEO solutions show that increasing polymer concentration influences elasticity, resulting in narrower cavity interfaces and reduced air volume attached to the sphere after cavity rupture. The asymmetry of the air cavity is diminished with increasing viscosity and is amplified in the presence of fluid elasticity. Insights into cavity shapes generated by the impact of a spherical body in a liquid, and correlating cavity dynamics with fluid properties, contribute to advancing knowledge in various fields, from solid–fluid interaction and rheology to biomechanics and biology.