  We report a new mechanism for nucleation in a monolayer of hexagonally packed
monodisperse droplet arrays. Upon cooling, we observe solidified droplets to
nucleate their supercooled neighbors giving rise to an autocatalytic-like
mechanism for accelerated crystallization. This collective mode of nucleation
depends on the strength and nature of droplet contacts. Intriguingly, the
statistical distribution of the solidified droplet clusters is found to be
independent of emulsion characteristics except surfactant. In contrast to
classical nucleation theory, our work highlights the need to consider
collective effects of nucleation in supercooled concentrated emulsions where
droplet crowding is inevitable.
