Vibrofluidized melting of geometrically cohesive granular media

Dry granular media composed of particles of special shapes (e.g. long rods or c-shaped particles) can display cohesive effects through particle geometry alone. We study the solid to gas transition in piles of c-shaped particles under vertical vibration as we vary acceleration and frequency. A cylindrical solid of particles is formed with wall angles near $90^\circ$ and is placed on a solid surface. For fixed frequency as acceleration increases, the pile undergoes two transitions. The first is from the solid-like state to a liquid-like state in which the wall angles relax but the mobile particles remain spatially localized. The second is from the liquid-like state to the gaseous state in which particles become separated (not entangled). Using video and accelerometer measurements, we record the temporal evolution of the spatial density and pile-plate collisional impulse. A critical energy scale, set by the particle geometry and gravitational potential energy, governs the liquid-gas transition.