Evaporation of Sessile Droplets

We first study the evaporation of small sessile droplets and discuss the importance of the thermal conductivity of the substrate on the evaporation process. We show how current evaporation models produce a significant error for droplet sizes below 500 µm. We developed a model that includes thermal effects, in particular, the thermal conductivity of the substrate that provides heat to the droplet to balance the latent heat of evaporation. It considers the whole time of evaporation with the pinned and the de-pinned stages by defining a virtual movement of the contact line that is related to the evolution of the contact angle and is based on experimental results. Our model is in agreement with our experimental results for droplets smaller than 500 µm with an error below 2%. Furthermore, we study the evaporation of line droplets with finite sizes and discuss the complex behavior of the contact lines during evaporation. We apply an energy formulation and show that the contact line starts receding from the two ends of line droplets with a contact angle above the receding contact angle of spherical droplets.