(594c) Separation of Particles during Drop Evaporation

Authors: 
Devlin, N. R., Purdue University
Harris, M. T., Purdue University

In this work, an evaporating droplet with two different sized colloidal particles is studied. During the evaporation process, the particles can be separated by their size into different rings. The finite element method was used to solve the governing equations. The fluid is assumed to be Newtonian and the droplet is assumed to be axisymmetric. The full momentum equations and continuity equation govern the fluid velocity and pressure within the droplet. The liquid evaporates and diffuses in the vapor space. The particle concentration inside the droplet is governed by the convection-diffusion equation.  Using this model, particle separation and deposition onto the substrate is analyzed throughout the evaporation process. In addition to the model, experiments have been performed to confirm the ring separation using a water droplet containing 1 μm and 3 μm polystyrene spheres.