Bifurcations in droplet collisions

We study bifurcations in the collision dynamics of micron-sized water droplets in air. Collisions are caused either by differential settling under gravity in a quiescent fluid, electrostatic attractions, or by a straining flow that brings the droplets together. We take into account hydrodynamic interactions between the droplets and the breakdown of the continuum approximation at short distances. We show how bifurcations of equilibria and grazing bifurcations explain the parameter dependence of the collision cross section.