Interaction of laser-produced Cavitation bubbles with elastic boundaries

The behavior of a laser-produced cavitation bubble near an elastic boundary as well as the deformation of the boundary induced by bubble motion are investigated by means of high-speed photography. The elastic boundary, used as a tissue phantom, consists of a polyacrylamide (PAA) gel whose elastic properties can be controlled by modifying the water content of the sample. The bubble dynamics is strongly dependent on the dimensionless distance γ= s/R_max between bubble and boundary and on the elastic properties of the boundary. The jetting behavior varies between unidirectional jets towards or away from the boundary, and formation of an annular jet which results in bubble splitting and subsequent formation of two very fast axial jets flowing simultaneously towards the boundary and away from it. The peak jet velocities near an elastic material are > 800 m/s, 6 times higher than close to a rigid boundary. The liquid jet penetrates PAA samples with an elastic modulus in the intermediate range. In this same range of elastic moduli and for small γ-values, PAA material is ejected into the surrounding liquid due to the elastic rebound of the sample surface. For softer samples, material is tom off the PAA sample during bubble collapse, if the bubble is produced close to the boundary.