The Effects of Substrate Temperature on the Final Shape of Evaporated Droplets of Aqueous Polymer Solution

When a drop of aqueous polymer solution dries on a solid substrate, the polymer is deposited in a coffee-ring shape on the surface of the substrate. This coffee-ring effect is due to the relatively high evaporation rate at the pinned three-phase contact line of the droplet that causes the aqueous polymer solution to move outward from the center of the drop in order to replenish the evaporated solvent at the edge. Decreasing the evaporation rate at the edge of the droplet can slow the outward flow of the fluid which then decreases the coffee-ring effect, thereby creating a more uniform polymer film on the substrate. This study investigates the effects of varying substrate temperatures on the final shape of an evaporated polymer droplet on a glass substrate. We have found that for different concentrations of the aqueous polymer solution, a decrease in substrate temperature is associated with a decrease in the coffee-ring effect and a more uniform polymer deposition.