3D Printed Microdroplet Curing: Unravelling the Physics of On-Spot Photopolymerization

Abstract

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.

Coalescence of 3D Polymeric Drops in the Presence of In Situ Photopolymerization

“…In situ photocuring-induced chemical reactions can significantly affect the spreading dynamics of liquid drops, as elucidated by our previous paper. 25 Here, we extend that study to probe the coalescence dynamics of polymeric drops in the presence of in situ curing and associated chemical reactions.…”

“…One important aspect of polymeric drop dynamics that has received very little attention is the effect of possible photocuring (and the associated chemical reaction-driven changes in the drop properties) during the drop dynamics. To the best of our knowledge, the only study to date that has captured the physics associated with the dynamics of polymeric drops with photocuring (thereby changing the drop properties) in detail has been our numerical study 25 probing the dynamics of the spreading of a photocurable, shear-thinning polymeric drop in the presence of in situ curing (driven by UV radiation). Our model captured UV radiation-driven photocuring and the associated chemical reactions, incorporated the effect of these reactions into the unsteady and flow-driven concentration distribution of the monomers and initiators (present inside the drop), and accounted for the photocuringdriven changes in drop viscosity and drop temperature while modeling the spreading dynamics of the drop.…”

“…Accordingly, following the same procedure as that adapted to obtain the corresponding bridge-height-vs-time variation for the intermediate regime for case 1 (see eq 25b), one would expect (see eq 30b); therefore, this simultaneous presence of the inertial and viscous forces balancing the capillary forces, while determining the bridge width, can provide a possible explanation of a scaling exponent of "0.33" (i.e., in between the exponent values of 0.5 and 0.3). In our previous paper, 25 we have identified such a scenario where the bridge width is being dictated in the presence of the combined viscous and inertial forces balancing the capillary forces.…”

Physically soft magnetic films and devices: fabrication, properties, printability, and applications

“…Modeling efforts are also underway for tackling more continuum-scale issues associated with the printing of polymerbased materials: for example, in recent studies from our group we used computational fluid dynamics modeling to capture the simultaneous curing and spreading of polymeric drops and effect of impact velocity on the coalescence of the polymeric drops. 98,99 Such knowledge is essential for understanding droplet-based 3D printing (such as aerosol-jet printing or inkjet printing) of polymer-based materials. Unlike the MD simulations, such CFD systems enable tackling simulation system sizes that match realistically with the actual experimental systems.…”

Moving Towards a Finer Way of Light-Cured Resin-Based Restorative Dental Materials: Recent Advances in Photoinitiating Systems Based on Iodonium Salts

“…The dynamically developing printing industry is a different direction of the application of photopolymerization, which enables printing on plastic or metal materials. Moreover, in recent years, a particular emphasis has been put on the use of photopolymerization processes for 3D-printing technology [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ], including stereolithography in the design and formation of three-dimensional models [ 34 ].…”