This e-mail is to announce that Nicole Devlin will be defending her dissertation, The Separation of Two Different Sized Particles Via Droplet Evaporation, on Monday, August 3rd, at 1:00 p.m. in FRNY 3062B. The dissertation is directed by Dr. Harris, and the abstract is below. All are welcome to attend. Abstract: An evaporating droplet with different sized particles was examined both computationally and experimentally. During evaporation, particles can naturally separate into concentric rings by size with one ring per particle size. The objective of this investigation was to determine factors that contribute to this separation process. Computationally, the finite element method was used to solve a transport model for the droplet fluid velocity in two directions (radial and axial), the pressure, the temperature inside the droplet, and the concentration of each particle size. Experimentally, an aqueous droplet with 1 µm and 3 µm polystyrene spheres was evaporated on a silicon substrate. It was determined that several factors contribute to particle separation. First, the surface tension driven Marangoni currents caused by evaporative cooling on the droplet surface significantly affect the separation process. The Marangoni currents keep the particles suspended in the droplet for the majority of the evaporation, which allows for separation by geometric constraints. A maximum packing concentration for the spheres was implemented in the simulations and without Marangoni currents, the maximum packing limit is reached quickly, before separation can occur. Second, gravity was determined to have a large effect on particle deposition. Pendant droplet simulations and experiments result in larger (3 µm) particles depositing in the center of the droplet and the smaller (1 µm) particles depositing on the edge of the droplet. The third investigation was a computational study on the influence of buoyancy-driven flow in an evaporation. It was determined that buoyancy-driven flow is present in the initial stages of droplet evaporation, especially when the environment is humid. And finally, an experimental investigation on the surface roughness and droplet contact line depinning on particle separation was conducted. Both high surface roughness and contact line depinning prevent the separation of particles in an evaporating droplet. Corwin Green Graduate Office Secretary School of Chemical Engineering Purdue University 480 Stadium Mall Drive West Lafayette, IN 47907 E-mail: csgreen@purdue.edu<mailto:csgreen@purdue.edu> www.engineering.purdue.edu/ChE<https://engineering.purdue.edu/ChE/index.html>