The stability of a paper coating filtercake and the influence of Brownian motion relative to absorption flow can be described using a particle dynamics model. For such a study, we assumed that the stability of a filtercake depends on the interrelation between particle diffusion and the hydrodynamic drag force caused by the absorption flow of liquid. We simulated particle diffusion using a Brownian motion model. Our investigation included monodisperse and polydisperse particle systems of electrostatically stabilized rigid spheres. We also varied system temperatures in some of the simulations. Results characterize the stability, microstructure, density profiles, and thicknesses of the filtercake. We concluded that particle diffusion disrupted the filtercake if the size of the particles was small or the temperature high. For dewatering rates typical of paper coating processes, the simulations show that only particles less than 0.2 μm are able to diffuse sufficiently to result in a solids density gradient over the thickness of the filtercake. In the polydisperse system, small particles can migrate within the filtercake at low dewatering rates. The solids concentration gradient observed in some cases appeared to be the result of filtercake surface roughness, partly caused by a size segregation effect rather than of the proposed thickening mechanism.
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