Observations on single drop formation from a capillary tube at low flow rates

The formation of organic drops from a capillary into a static water phase is studied experimentally at low flow rates (50–500 μl/min) using a high-speed video camera. Four different stages of the drop formation are identified and various geometric parameters, such as current contact angle (angle of the interface with the top capillary wall), drop height, neck length, mean drop growth velocity and drop wetted diameter on the top capillary wall are measured. It is found that the changes in current contact angle during the formation process follow different trends which coincide with different stages of drop formation. The attaching and detaching forces which act on the drop during formation are calculated based on the experimentally measured parameters. It is found that by using the current contact angle on the interfacial tension force calculation, the forces balance for most of the period of drop formation until the drop detachment stage.