Numerical Modeling of In-Situ Curing of a Photopolymerizing and Spreading Drop with Applications in 3D-Printing*

The key to understand droplet-based direct writing (DW) printing processes like Aerosol Jet Printing (AJP), Ink-jet printing, syringe printing, etc. is to quantify the behavior of ink droplets during deposition. For instance, the resolution of the print depends on minimum drop radius and also to the extent of the droplet spread (spreading radius). In this study, we investigate the spreading behavior of a polymer drop in conditions similar to that of the Aerosol Jet Printing (AJP) process. Here, the drop is undergoing simultaneous spreading and photopolymerization with timescales of τ_s and τ_p respectively. We conduct a comparative study of the droplet behavior for two cases, τ_s << τ_p , where the spreading is much faster than polymerization and τ_s ~ τ_p, where the spreading and polymerization have similar timescales. Droplet spreading is unaffected by the polymerization process in the former case. However, in the latter case the spreading of the droplet is hindered by the polymerization process due to a tremendous increase in viscosity. We further study this complex thermo-fluid-solutal dynamics by comparing the time dependent curing profiles for the two cases.