When oil drops in a continuous water phase move from the hydrophilic to the hydrophobic section of a microchannel, they can be controlled to either adhere or not adhere on the channel by changing the capillary number. Using experiments and a model for the thin film flow, we show that the critical capillary number for adhesion is approximately Ca ˜ D3/4/d3/2, where D and d is the length of the droplet and the inner dimension of the microchannel, respectively. As one application of these ideas, droplet adhesion is demonstrated as a promising technology for recycling of emulsions in droplet microfluidics.