2008 NSTI Nanotechnology Conference and Trade Show - Nanotech 2008 - 11th Annual

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Clean Technology 2008

Generalized model for the aggregation rate of colloidal nanoparticles and clusters induced by shear in the presence of repulsive interactions

M. Lattuada, M. Morbidelli
ETH Zurich, CH

Keywords:
nanoparticles, fractal clusters, coagulation, aggregation rate, shear

Abstract:
Coagulation of colloidal nanoparticles in the presence of shear is a key step in processing of many particulate materials, polymeric nanoparticles, food products etc. In the case of charged nanoparticles, coagulation is usually carried out by completely screening all electrostatic interactions and simultaneously shearing the suspension. However, for certain applications, the addition of large amounts of electrolytes is not beneficial for subsequent processing of the material and its removal might be necessary. In order to be able to operate under low electrolyte concentrations the still poorly understood mechanism of shear induced aggregation in the presence of repusive barrier needs to be understood. In this work, we have performed detailed simulations of the aggregation rate of both colloidal nanoparticles and fractal clusters in the presence of both linear shear flow and repulsive interactions, by numerical solution of the convection-diffusion equation for the pair probability function, from which aggregation rates are computed. Using a simplified model we have interpreted the results of the rigorous calculation and provided a simple criterion to determine the relative importance of all mechanisms involved in the aggregation. It is found that sufficiently high shear can lead to the same aggregation rates found in fully destabilized suspensions.


Nanotech 2008 Conference Program Abstract