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Electrophoresis in concentrated suspensions

- Leader : Peters François

- Collaborators within the LPMC : Lemaire Élisabeth, Lobry Laurent

- External collaborators : Perez Alberto T., Montoya C. (Departamento de Electromagnetismo y Electronica, University of Séville)

- Technological platforms : Center for Micro & Nanorheometry

- Description :

Electrophoresis is the motion of electrically charged colloidal particles under the influence of an electric field. This phenomenon is well understood in the case of diluted dispersions, even if a precise description of the particle surface is required, especially as for its electrochemical properties. On the other hand, in concentrated suspensions, the particles interact with each other, because of the electric field and velocity field that they produce. The strength of these interactions is stronger if the diffuse charge layer around the particles is thick. In that case, the influence on the electrophoretic mobility of the particle concentration, of their charge, of the solvent properties (permittivity, conductivity) is not clearly understood yet. Moreover, the optical mobility measurement techniques (microelectrophoresis, dynamic light scattering), that are classical in diluted suspensions, are made difficult for such high solid concentrations that the suspension becomes turbid.

We have performed electrophoretic light scattering measurements in silica particles suspensions, 80nm in particle diameter, up to solid volume fraction of \phi=5.4%. The suspending liquid, a mixture of toluene (70%) and ethanol (30%) has been chosen as to match the refractive index of the particles, in order to avoid multiple light scattering.

An approximately linear dependence of the mobility on the particle concentration has been found, \mu_E=\mu_0(1+S\phi), with a relative slope S= 8, together with a strong polydispersity of the mobility (\sim 0.6\mu_S). The later property has been seldom studied up to now, but it may provide information on the mechanisms that are responsible for the dependence of the mobility on the solid volume fraction.

In the system that we are interested in, the double layer is very thick (around the particles diameter) due to the low electric polarizability of the solvent. Our experimental measurements are in quite good agreement with models that take account of electric and hydrodynamic interactions between particles due to double layer overlapping.

This project has now shown real progress and is no longer part of our main priorities. However, we wish to carry out complementary experiments by further augmenting the volume fraction of the particles towards increasing the influence of the interactions, and by working with a better control on the physicochemical properties of the surface.


Fluides & Matériaux Complexes, Rhéologie des Suspensions