Sticky bubbles

We discuss the physical forces that are required to remove an air bubble immersed in a liquid from a corner. This is relevant for inkjet printing technology, as the presence of air bubbles in the channels of a printhead perturbs the jetting of droplets. A simple strategy to remove the bubble is to ush the ink past the bubble by providing a high pressure pulse. In this report we rst compute the viscous drag forces that such a ow exerts on the bubble. Then, we compare this to the \sticking forces" on the bubble, due to the capillary interaction with the wall. From this we can estimate the required ow velocities for bubble removal, as a function of channel geometry, contact angle and ink properties. Finally, we investigate other ways to exert a force on a trapped bubble. In particular we focus on forces induced by electric elds which can alter the contact angle of the drop, or by locally applying thermal gradients. Once again, these forces are compared to the sticking forces to identify the parameters where the bubble can be removed.