Buckling-induced jamming in channel flow of particle rafts

We report on observations of the flow of plastic particles floating on the surface of water in a rectangular channel. The system is driven by moving one wall of the channel at a constant velocity. The opposite side of the channel is open, and the particles are pushed into a region free of material. During the flow, video of the particle motions is captured, and the average force on the pushing wall is measured. We have studied particle shapes that are both circular disks and rectangular bars. We find that when the rectangular bars form a layer at the side walls of the channel (whether or not the central region is filled with disks or additional rectangular bars), the system exhibits sudden increases and decreases in the average force on the driving wall. This behavior is consistent with the existence of jamming in the system. We report on the shape and velocity dependence of these force fluctuations, and the evidence that buckling of the rectangular blocks at the wall is responsible for generating the jamming dynamics.