Interactions between cavitation bubbles and free surfaces of non-Newtonian polymer solutions

The interaction between cavitation bubbles and free surfaces in non-Newtonian biological fluid holds significant importance for biomedical fields like drug delivery and disease treatment. This paper investigates the influences of elasticity and shear-thinning of non-Newtonian fluid on the interaction between cavitation bubbles and free surfaces by performing visualization experiments on the laser-induced cavitation bubbles near the free surfaces of the water and carboxymethyl cellulose and polyacrylamide solutions with the concentrations of 500–5000 ppm at different dimensionless standoff distances. The results show that the evolutions of free surface in all solutions can be divided into six patterns of water mounds. The elasticity and shear-thinning exhibit significant effects on the four patterns at smaller dimensionless standoff distances (breaking wrinkles, spraying water film, crown, and swallowed water spike) and the evolutions of cavitation bubbles in the corresponding cases. The resultant differences lie in the morphology and migration of bubbles and the stability and morphology of the water spike and water skirt. Combining with the quantitative analyses, it can be concluded that elasticity inhibits the movement and pinch-off of water spike, water skirt expansion, bubble jet motion, and bubble growth and migration within its second period. Conversely, shear-thinning could counteract the inhibitory effects of elasticity in the solutions with lower concentrations, promoting the rise in water spike, water skirt expansion, and bubble jet motion. Finally, the influence mechanisms of elasticity and shear-thinning on the evolution of free surface and cavitation bubble dynamics are revealed from the perspective of the deformation of polymer molecular chains.