Visualize the drying stress of a drop containing colloidal particules with a deformable surface
When you paint a surface, the drying can cause delamination or cracks in the coating. These forces come from the material contraction when the solvant evaporates. By using deformable surfaces, we visualize the drying stress development. Here, we use thin membranes floating on a liquid bath. A drop containing colloidal silica nanoparticles is deposited in the center. As the evaporation proceeds, the membrane wrinkles and their length teaches us about the drying stress in the drop.
These suspensions are usually polydisperse and we studied the effect of polydispersity on the drying stress. Interestingly, the stress is dominated by the largest particles of the distribution. Thus, adding large particles, even at low number, decreases the drying stress and can limit phenomena such as delamination.
How to peel an elastic sheet with nanoparticles
When a water droplet is left on a flexible sheet, the sheet can bend due to the capillary forces as shown Charlotte Py in the group of Benoît Roman et José Bico. This leads to capillary origami. However, if adhesion between the substrate and the sheet are too strong, these capillary forces may not be sufficient. Thus, we need to find another way to peel the sheet. If we cover this sheet with a drying solution of nanoparticles, large stresses build up which leads to the bending and the peeling of the sheet without any human action!