SEDIMENTATION TO FORM ROUGH, QUASI-ONE-DIMENSIONAL INTERFACES

The quasi-two-dimensional sedimentation of silica particles in viscous fluids results in quasi-one-dimensional rough surfaces. These surface s are rough on all length scales between the particle size and the cel l size, but different roughness exponents are observed in two well def ined length-scale regimes. The range of hydrodynamic forces should pla y an important role in determining which, if either, length-scale regi me shows universal properties. The strong similarity between the heigh t-height correlations of the surface and the density-density correlati ons inside the flow at longer length scales suggests that the roughnes s at longer length scales is very closely tied to the hydrodynamic int eractions in the fluid. Measurements have been performed at three diff erent cell aspect ratios and at three different fluid viscosities and in no case is there an observable change in the crossover length scale of the system.