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Accueil du site > Séminaires > Archives > Archives 2016 > Watching paint dry

Watching paint dry

Lucas Goehring, Max Planck Institute, Göttingen, Germany

25 avril 2016

Colloidal dispersions, such as those used in paints, ceramics, or in the production of photonic crystals, undergo a series of dramatic instabilities as they change from a liquid to a solid. A drying film may crystallize into beautiful artificial opals, or buckle, curl, crack, and deform into a shattered mess, all in response to capillary forces that may reach several atmospheres in pressure. We study the liquid-solid transition of a drying colloidal dispersion of charged latex spheres - paint. We show how solidification occurs in stages, as the material orders by long range forces, forming a glass, then aggregates into a solid film. For example, one can infer the nanoscopic response of the colloidal dispersion, by watching the colours change under the microscope. The flow of water during such a process breaks the symmetry of the film, and causes a series of unexpected, yet robust, features of drying, including a structural anisotropy of the dry film, birefringence, shear banding, and a preferred orientation of any paint cracks.