Initial regime of drop coalescence

Abstract

What is the initial regime of coalescence when two drops just touch at a point? This long-standing problem has proven formidable because of the smallness of the bridge that is required to connect the drops at the initial instant in any continuum simulation. Here, initial bridge radii, heights, and radii of curvature as small as 10${}^{\ensuremath{-}6}$, 10${}^{\ensuremath{-}12}$, and 10${}^{\ensuremath{-}18}$ are achieved, showing that coalescence always begins in a Stokes regime. The inertially limited viscous regime is shown to be a Taylor-Culick-like regime seen only when drops are initially separated by a finite distance.