Evaporation-Driven Transport in Inkjet Printing Droplets

The wayaprinted ink droplet dries is just as important as how it is deposited. During evaporation, the liquid inside the droplet circulates, the interface cools, and the solvent composition changes. These coupled processes control where non-volatile solutes and particles accumulate, which ultimately affects the uniformity, microstructure, and electrical performance of printed metallic features. In this work, we present a time-dependent multiphysics model of a sessile reactive silver-ink droplet composed of a binary solvent mixture (water and ethylene glycol) on a heated substrate. A two-dimensional axisymmetric model is implemented in COMSOL Multiphysics by coupling Laminar Flow (Navier Stokes), Heat Transfer in Fluids, and Transport of Concentrated Species (Maxwell–Stefan diffusion), along with a moving interface representation to account for evaporation-driven shrinkage. The formulation captures evaporation-driven capillary flow, thermocapillary Marangoni stresses caused by evaporative cooling, and solutal Marangoni stresses caused by preferential evaporation and solvent segregation. The simulations predict (i) strong, transient internal circulation; (ii) spatially non-uniform temperature fields; and (iii) progressive enrichment of ethylene glycol near the liquid–vapor interface and especially near the contact line. These results provide a practical, physics-based framework to interpret common drying outcomes such as ring-like deposition versus more uniform coatings, and they offer guidance for optimizing solvent ratios and substrate temperature in inkjet printing.