The pendant drop experiment for aggregates of cohesive granular particles†

Abstract

The pendant drop experiment can be used to study the interfacial tension of a liquid. Here we perform a similar experiment for a granular system. When a dense aggregate of cohesive particles extrudes from an orifice, a cluster of particles detaches, similar to the detachment of a liquid drop. We investigate the volume of the clusters formed from close-packed cohesive oil droplets in an aqueous solution. Our findings reveal that the volume of the clusters depends on the size of the orifice as well as the cohesion strength. Interestingly, we observe that the droplet size does not significantly impact the average cluster volume. We establish a simple scaling law that governs the size of a granular cluster which differs from that of a classic pendant drop. We propose that the key difference between continuum and granular systems is the constraints on rearrangements within the cohesive particles that prevent the clusters from adopting a minimal surface structure, as is the case for a classic pendant drop.