3D Printing of Ultrahigh Viscosity Nanoparticle Suspensions via Acoustophoretic Liquefaction

In this work, we reported an acoustic liquefaction approach to enhance the flow of yield stress fluids for digital light processing (DLP) based 3D printing. This enhanced flow enables the processing of ultrahigh viscosity resins, having apparent viscosity bigger than 3,700 Pa s at 0.01 s^-1shear rates, with high silica particles loading in a silicone photopolymer. We simulated the acousto-mechanical coupling in the DLP resin feed system at different agitation frequencies to elucidate the mechanism of the enhanced flow. From the simulation, the resulting local resin flow velocities up to 112 mm s^-1 at acoustic transduction frequencies of 110 s^-1. We successfully printed complex geometries from highly loaded particle suspensions using these results. Compared to the neat photopolymer, these printed objects increase the tensile toughness by 2,000%. Beyond an increase in processible viscosities, acoustophoretic liquefaction creates a transient reduction in apparent viscosity that promotes resin recirculation to reduce "over-curing" of previously printed layers, which improves the printed feature resolution by over 25%. Also, acoustophoretic liquefaction decreases viscous adhesion to increase printable object sizes by over 5 times, increases printable object sizes more than 50 times, and can build parts more than 3 times faster when compared to conventional methods.