When a suspension drop evaporates, it leaves behind a drying stain. Examples of these drying stains encountered in daily life are coffee or tea stains on a table top, mineral rings on glassware that comes out of the dishwasher, or the salt deposits on the streets in winter. Drying stains are also present in industrial processes, for example in the printing and coating industry, where the non-uniform drying of drops can be a problem. Pattern formation by evaporation of colloidal suspension drops can however also be used as a tool to manufacture tiny structures on a scale where direct manipulation is not possible. In order to either prevent ring-stain formation or control the type of stains that are formed, one needs to understand the basic physics of evaporating drops and their internal fluid flow. In this thesis we focused on the fundamentals of drop evaporation, evaporation-driven flow in drying drops, and the subsequent particle transport and deposition. We used a simple model system: a macroscopic sessile water drop that evaporates under atmospheric conditions and contains spherical polystyrene particles. By evaporation of these colloidal suspension drops remarkable, highly-ordered drying patterns were obtained. The particle arrangement inside these patterns originates from a competition between particle diffusion and convection and therefore depends on the evaporation rate of the drop and the particle size.
|Award date||19 Apr 2013|
|Place of Publication||Enschede|
|Publication status||Published - 19 Apr 2013|