Numerical Simulation of Evaporation of Ethanol-Water Mixture Droplets on Isothermal and Heated Substrates

In many printing technologies involving multicomponent liquids, the deposition and printing quality depend on the small-scale transport processes present. For liquids with dispersed particles, the internal flow within the droplet and the evaporation process control the structure of the deposition pattern on the substrate. In many situations, the velocity field inside microdroplets is often subject to either thermal or solutal Marangoni convection. Therefore, to achieve more uniform material deposition, the surface tension-driven flow should be controlled and the effect of different fluid and chemical parameters should be identified. Here, we employ an axisymmetric numerical model to study droplet spreading and evaporation on isothermal and heated substrates. For ethanol-water droplets, the effects of the initial contact angle and initial ethanol concentration inside the droplet (solutal Marangoni number) have been studied. We explore the role of the initial ethanol concentration on the magnitude and structure of the internal flows for binary mixture droplets. In addition, we show that certain combinations of initial contact angle and initial ethanol concentration can lead to a more uniform deposition of dispersed particles after all of the liquid has been evaporated.