Separation of Colloidal Particles in a Packed Column using Depletion Forces
Guzman, Francisco J.
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Depletion forces were used to separate an equinumber density binary dispersion of 1.5 and 0.82 Âµm polystyrene sulfate (PS) particles. Experiments consisted of injecting a pulse of a binary dispersion of PS particles into the inlet of a packed bed of 0.5 mm silica collector beads. Prior to injection, a carrier fluid of either KCl and KOH electrolyte or a silica nanoparticle dispersion was flowing through the column at steady state. When the carrier fluid was a dispersion of silica nanoparticles, the ratio of PS particles in the column outlet would change from 1:1 big to small particles to slightly over 2:1. This implies that more of the smaller 0.82 Âµm particles were being trapped on the surface of the collector beads due to depletion forces. Experiments with a single particle type (either 1.5 or 0.82 Âµm PS particle) were also done and correlated with the binary dispersion measurements. Potential energy profiles between a PS particle and a flat silica plate were calculated. The secondary energy barrier for the 1.5 Âµm particles was two times greater than for the 0.82 Âµm particles. Hence, the 0.82 Âµm particles were more likely to overcome the energy barrier and get trapped on the surface of the collector beads. Although the potential energy profiles were calculated at equilibrium, they can be used as a tool in finding the optimal conditions for separation.
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