Vishal Sankar Sivasankar 1, Harnoor Singh Sachar 1, Shayandev Sinha 2, Daniel R. Hines 3, and Siddhartha Das1
1 CALCE, Center for Advanced Life Cycle Engineering, Department of Mechanical Engineering, University of Maryland, College Park, Maryland 20742, USA
2 The Rowland Institute at Harvard, Harvard University, Cambridge, Massachusetts 02142, USA
3 Laboratory for Physical Sciences, College Park, Maryland 20740, USA
Droplet-based direct-write printing (one form of 3D printing) methods, like inkjet printing, aerosol jet printing (AJP), etc., have changed our ideas about bottom-up additive manufacturing. AJP is capable of 3D printing by depositing microdroplets that lead to certain benefits in 3D printing of microscale structures. Here, we study the in situ photopolymerization-based curing of a microdroplet. The droplet is simultaneously spreading and curing, which leads to the rise of two time scales, the spreading time scale (τs) and the photopolymerization time scale (τp). When τs ≪ τp, the spreading occurs very fast and is independent of polymerization. If the time scales are of the same order (τs ∼ τp), the spreading is significantly affected by the polymerization. For this case, a progressive increase in the viscosity of the drop during the spreading ensures a much slower spreading and also a much weaker extent of spreading (i.e., the spreading ceases at a much smaller spreading radius of the drop). This complex thermofluidics is eventually manifested as distinct differences in the time-dependent velocity, temperature, and curing (or equivalently, monomer concentration) profiles within the drop between the two cases.