Angle of repose of a frictionless pile of microscopic, cohesive oil droplets

The angle of repose is a familiar feature in piles of granular materials like grain and sand. While interparticle forces and particle packing determine how granular systems spread, frictional particles often form conical piles with a characteristic angle of repose. Here, we investigate the angle of repose formed by microscopic, frictionless, cohesive oil droplets. In our experiments, a continuous flow of monodisperse oil droplets feeds a growing pile confined within a cylindrical silo. By systematically varying the cohesion strength and droplet size, we investigate the role of these parameters on the angle of repose and present a theory that explains the results.