  We investigate experimentally and theoretically the interactions between a
cavitation bubble and a hemispherical pendant oil droplet immersed in water. In
experiments, the cavitation bubble is generated by a focused laser pulse right
below the pendant droplet with well-controlled bubble-wall distances and
bubble-droplet size ratios. By high-speed imaging, four typical interactions
are observed, namely, oil droplet rupture, water droplet entrapment, oil
droplet large deformation, and oil droplet mild deformation. The bubble jetting
at the end of collapse and the migration of the bubble centroid are
particularly different in each bubble-droplet interaction. We propose
theoretical models based on the method of images for calculating the Kelvin
impulse and the anisotropy parameter which quantitatively reflects the
migration of the bubble centroid at the end of the collapse. Finally, we
explain that a combination of the Weber number and the anisotropy parameter
determines the regimes of the bubble-droplet interactions.
