Experimental and computational study of the effect of the system size on rough surfaces formed by sedimenting particles in quasi-two-dimensions

The roughness exponent of surfaces obtained by dispersing silica spheres through a viscous fluid in a quasi-two-dimensional cell is examined using experimental and computational methods. The cell consists of two glass plates separated by a gap which is comparable in size to the diameter of the beads. We have studied the effect of changing the gap between the plates to a limit of about twice the diameter of the beads. If a conventional scaling analysis is performed, the roughness exponent is found to be robust against changes in the gap between the plates. The surfaces formed have two roughness exponents in two length scales, which have a crossover length of about 1 cm.; however, the computational results do not show the same crossover behavior. The single exponent obtained from the simulations stays between the two roughness exponents obtained in the experiments.