Abstract: Methods of determining a first position at which a dispersed phase droplet wets a surface of a channel are provided herein. The methods include immersing the dispersed phase droplet in a continuous phase fluid, wherein the continuous phase fluid is immiscible with the dispersed phase droplet, subsequently flowing the dispersed phase droplet in the continuous phase through the channel at a dispersed phase droplet velocity, wherein the dispersed phase droplet is separated from the surface by a film of the continuous phase fluid having a film thickness, and reducing the film thickness to rupture the film at the first position, wherein the droplet wets the surface at the first position.