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Sedimentation and electrophoresis of a porous floc and a colloidal particle coated with polyelectrolytes
Institution:1. Department of Mathematics, Indian Institute of Technology Kharagpur, Kharagpur 721302, India;2. Advanced Technology Development Centre, Indian Institute of Technology Kharagpur, Kharagpur 721302, India;3. Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India;1. Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba-shi, Ibaraki 305-8572, Japan;2. Laboratory of Physical Chemistry and Colloid Science, Wageningen University, Dreijenplein 6, 6307 HB Wageningen, The Netherlands;3. School of Water Conservancy, North China University of Water Resources and Electric Power, No. 36, Beihuan Road, Zhengzhou, China
Abstract:Sedimentation and electrophoresis of porous colloid complex; a colloidal floc and a colloidal particle covered with adsorbed polyelectrolytes are visited to examine the characteristic length of the transport phenomena. In the sedimentation, the overall size of a floc is dominative in the determination of Stokes drag, while the permeability is determined by the largest pore in the floc. This picture is important when break-up of flocs in a turbulent flow is considered. When a colloidal particles is coated with polyelectrolytes, the characteristic length for diffusion is that of the diameter of colloidal particle plus protruding part of polymer chain adsorbed onto the particle. On the other hand, when the porous colloid complex is placed in the electric field, fluid surrounding the complex can easily penetrate into the complex by means of electro-osmosis. The diffusive part of electric double layer located inside of the complex is the source of strong driving force of this osmotic flow. Flow generated in this regime can be treated as a sort of shear driven. The characteristic length scale for transport phenomena is the Debye length or the distance between charged segments. These lengths are much shorter than the case of sedimentation and Brownian diffusion.
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