Influence of substrate elasticity on particle deposition patterns from evaporating water-silica suspension droplets

We investigated the evaporation of sessile droplets of water-silica suspensions on deformable polydimethylsiloxane substrates with Young's moduli ranging from 0.2 to 1.5 MPa. We show that substrate elasticity can be employed to control the evaporation patterns and reduce the so-called coffee-staining. The presented method, unlike previously investigated methods, requires no modification of the liquid or the particles. The ratio between deposit height in the center and at the rim of the pattern - which is an important characterizing parameter of a coffee stain - decreases with decreasing Young's modulus. This is due to the smaller receding contact angle and the higher contact line velocity of a droplet on a softer substrate. These experimental findings are reproduced by a model for the contact line speed that considers capillary forces, viscoelastic dissipation, and contact line friction.