(407a) The Effect of Bubbles On Liquid Transfer During Printing

The transfer of liquid from one surface to another is a key stage in industrial printing processes. A potential complication is the entrapment of air bubbles, which can alter the amount of liquid transferred to the substrate, and can produce defects if the bubble does not burst before drying. To better understand this effect, we use flow visualization to study the stretching of liquid bridges with a single bubble over a range of capillary numbers. If the two solid surfaces bounding the liquid bridge are made of the same material, then the dynamics of the gas-liquid interface between the drop and the surrounding air are found to be the same during stretching both with and without a bubble; thus, the volume of fluid (liquid or liquid plus bubble) transferred to the moving surface is the same in both cases, regardless of the dynamics of the bubble. Therefore the surface to which the bubble transfers will receive less liquid than if no bubble were present. If the two surfaces bounding the liquid bridge are made of different materials, a wettability difference will drive the liquid towards the more wettable surface. However, the dynamics of the bubble depend on the choice of surfaces and the capillary number.