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Joseph Paulsen

University of Chicago
Ultrafast Experiments on Liquid Drop Coalescence
During coalescence, two drops first touch and then merge, as a liquid bridge grows from initially microscopic scales to a macroscopic size comparable to the drop diameter. The initial dynamics of coalescence are expected to be universal, owing to a singularity in the Laplace pressure, which diverges when the curvature of the liquid interface is infinite at the point where the drops first touch. Conventionally, this process has been thought to have just two regimes: a highly viscous one dominated by macroscopic flows pulling the two drops together and an inertial one described by local deformations near the growing neck. We use a combination of high-speed imaging and electrical measurements to reveal three main surprises: a late viscous-to-inertial crossover, a new dynamical regime, and the meager effect of an ambient fluid.
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