Visualization of the breakdown of dilute particles gels during steady-shear |
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Authors: | R Folkersma Alois J G van Diemen Jozua Laven Gert A J van der Plas Hans N Stein |
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Institution: | (1) Laboratory of Colloid Chemistry Department of Chemical Engineering Eindhoven University of Technology P.O. Box 513 NL-5600 MB Eindhoven The Netherlands E-mail: r.folkersma@tue.nl, NL;(2) Fluid Dynamics Laboratory Energy Technology Division Department of Mechanical Engineering Eindhoven University of Technology P.O. Box 513 NL-5600 MB Eindhoven The Netherlands, NL |
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Abstract: | A feature of models concerning the rheology of coagulated suspensions is the development of shear planes. An experimental
set-up was developed in which we investigated, by visual analysis, whether shear planes really develop in such systems during
steady-shear. A transparent coagulated PTFE dispersion was used, in which the refractive indices of the continuous and dispersed
phases were matched, for the formation of a gel. Coagulation was effected by adding NaCl to a concentration of 0.5 M. Polystyrene
particles were built into the gel structure as tracer particles. During steady-shear the velocities and trajectories of the
tracer particles were analyzed by Particle Tracking Velocimetry (PTV). Indeed layers with approximately the same velocity
were observed for a coagulated PTFE-gel, during steady-shear. Deviations from rectilinear motion of the tracer particles were
observed. These observations correspond with the assumptions of the giant floc model in which the shear is not distributed
homogeneously, but limited to certain shear planes. Deviations from rectilinear motion of the tracer particles in a dilute
gel correspond with the results found by Folkersma et al. (1998) in which the distance by which a moving particle entrains
its neighbours was assumed to be larger at low volume fractions (≈0.1) than at high volume fractions (≈0.4).
Received: 7 May 1998 Accepted: 31 August 1998 |
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Keywords: | Gels steady-shear PTV tracer particles |
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