Composite Ink Extrusion Behaviors in Direct Ink Writing with Acoustic Focusing

Intra-nozzle microparticle positioning methods can impose structural and functional gradients in 3D printed components. One such method is direct ink writing with acoustic focusing (DIWA), wherein a polymer fluid with suspended microparticles flows through a microfluidics channel. A piezoelectric actuator establishes a standing wave in the channel, which co-orients and directs particles to the wave nodes. Using the channel as a direct-write nozzle, we can print filaments with controlled spatial particle distributions. Because drag inhibits acoustic focusing, DIWA inks must be less viscous than conventional direct write inks. In this previously unexplored viscosity domain, we experimentally characterize how surface energies and viscous dissipation influence internal and external filament deformation, which indicate the quality and reliability of DIWA extrusion. Using digital image analysis to measure dynamic contact line positions, filament curvatures, and particle movement, we quantify nozzle wetting, filament stability, and maintenance of spatial particle distributions. By mapping these metrics across extrusion and raster speeds, we measure how the boundaries of the printable region vary in terms of ink composition, nozzle and substrate surface energies, and process parameters.