Drop formation instabilities induced by entrapped gas bubbles

During the formation of a liquid drop out of a capillary tube, instabilities can appear which cause an "instantaneous" variation in the drop volume. An analytical treatment of this phenomenon, which takes into account the presence of entrapped gas bubbles to explain the experimental observations is presented. A nondimensional number (called the Bubble Stability Number) has been derived, describing the influence of different experimental parameters (surface tension, radius of the capillary tube, external pressure, and volume of the entrapped gas) in determining the region of stable growth. Applications of this theory to systems which can present this type of instability are also discussed.