Droplets of Polymers
Résumé
Drying of a sessile drop of polymer solutions results in intriguing complex shapes. Due to the nonuniform evaporative flux from the surface of the sessile drop, the evaporation-driven flow inside the drop may distribute the polymers in an irregular and undesirable manner. A modification of the rheological properties of the system and the occurrence of instabilities take place. As a result, a nonuniform deposit is left. Understanding the broad variety of final morphologies is highly relevant to coating processes or biointerface mechanics, for instance. They represent also a particularly spectacular example in the growing field of surface instabilities. Coupling the flow of a liquid phase and the mechanical instabilities of elastic material governs the final morphology of the sessile drop. Indeed, under solvent loss, polymer accumulates, resulting in the formation of an elastic skin. Depending on the experimental conditions (drying conditions, contact angle and polymer concentration), different modes of deformation can take place: axisymmetric or secondary instabilities that break the axisymmetry can be observed.