Coalescence of droplets due to a constant force interaction in a quiescent viscous fluid

Acantilevered-capillary force apparatus is used to study the time scale for the coalescence of two droplets compressed together with a constant force. Power-law trends for the coalescence time as a function of droplet radius and compression force are experimentally measured. The measurements are compared against several different scaling theories from the literature. One of the existing theories is found to correctly predict the dependence on the droplet radius, but all of the theories overpredict the dependence on the force. A transition is also observed in the measured drainage time from a small variation around a single deterministic value for droplets with a radius of 125 mu m or less to a broad distribution of drainage times for droplets with a radius of 150 mu m. A qualitative explanation for this transition is provided via scaling arguments.