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By using a solvent counterflow (i.e., fluidization) to prevent sedimentation of charged silica spheres, we have established a steady state polycrystalline colloidal suspension of uniform concentration. With this technique we varied the steady state concentration of a single sample by simply changing the flow rate. Bragg scattering from the fluidized bed allowed for direct investigation of its crystal structure, stability, uniformity, and volume fraction, while the interparticle interactions were directly measured from shear resonances of the bulk. For strongly repulsive interactions we found that the particles formed an fcc lattice and sedimented considerably more slowly than when in a highly disordered state.
Rutgers et al. (Mon,) studied this question.