Shape oscillations of a bubble or drop attached to a capillary tip

Abstract The oscillation dynamics of bubbles and drops that are attached to the tip of a capillary are experimentally investigated to test the applicability of simplified linear analyses to real-world situations. The experiments are performed with 0.7–2.6 mm air bubbles in pure water (without surfactants) and with 0.7–1.3 mm drops of pure water. The bubbles or drops are excited by the vertical motion of the capillary. The consequent shape oscillations, which are recorded by a high-speed camera, are processed to determine the oscillation eigenmodes (their frequencies, shapes, and damping rates). If the bubbles or drops are sufficiently small to preserve the spherical static shapes, the measured characteristics of the eigenmodes will correspond to the analyses. If the bubble or drop size is sufficiently large to form a neck, the eigenmode frequency decreases and the shape oscillations will correspond to those of a free bubble. The reduction in eigenmode frequency is correlated with the ratio of the actual volume of the bubble to the detachment volume of the bubble.