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JSM-Seminar: Drying of colloidal suspensions in confined geometries

Jean-Baptiste Salmon, LOF, Pessac, France, (ICS-3)

16.Feb.2012 11:00
Lecture Hall, PGI/ICS, on Thursday


We investigated the drying of binary mixtures (colloidal suspensions, solutions,…) in a confined geometry: a droplet squashed between two circular plates. This axis-symmetrical confined geometry allows a neat control of the vapor removal from the edge of the droplet toward the edge of the wafers and therefore provides a simple way to tune the drying. I will present a model, based on simple transport equations for binary mixtures, that describes the concentration process of the solute inside the droplet. We show that it is possible to estimate both the collective diffusion coefficient and the activity of the drying mixture, from the combined measurement of the evaporation kinetics and of the concentration field of solute within the droplet [1].

 I will then discuss briefly experiments performed on “Hard-Sphere” suspensions in such a geometry, and its comparison with our model []. I will also present in more details recent experiments performed on bloc copolymer solutions. Thanks to original Raman imaging experiments, we are able to access to the polymer concentration field within the droplet during drying, and we thus estimate the phase diagram of the complex fluid, its activity and its mutual diffusion coefficient [3].

 Finally, such drying experiments generate buyoancy-induced flows due to unavoidable concentration gradients that develop within the confined geometry. In a more general context and thanks to original experiments (microfluidic flows, etc…), I will demonstrate that this natural convection has a negligible influence on the gradient of concentration that generate them, but can disperse very efficiently colloidal species [4].

[1] Evaporation of solutions and colloidal dispersions in confined droplets
L. Daubersies, J.-B. Salmon, Phys. Rev. E 84, 031406 (2011)

 [2] Drying of a colloidal suspension in confined geometry
J. Leng, Phys. Rev. E 82, 021405 (2010)

 [3] Confined drying of a drop of a complex fluid: estimation of phase diagram, activity, and mutual diffusion coefficient
L. Daubersies, J. Leng, J.-B. Salmon (submitted 2012)

 [4] Solutal convection in confined geometries: enhancement of colloidal transport
B. Selva, L. Daubersies, J.-B. Salmon (submitted 2012)





Prof. Dr. M.P. Lettinga
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