Scaling relationships for direct ink writing with acoustic focusing

Abstract

Novel methods to control the microstructures of multiphase extruded materials are needed to control spatial variations in structural and functional properties in additively manufactured components. One promising method is acoustic focusing, wherein microparticles suspended in fluids flowing through a silicon microfluidic channel are manipulated by establishing an acoustic wave in the channel. Acoustic focusing quality depends on factors including nozzle and particle geometries, acoustic pressure, matrix rheology, and flow characteristics. Using these factors, we experimentally verified scaling relationships governing acoustic focusing based on classical acoustic forces, using ceramic microspheres in epoxy resin. Further experiments characterized focusing behavior in more complex shear-thinning matrices composed of epoxy resin, fumed silica, and acetone. We designed image processing methods to quantify particle focusing and form holding (the ink’s ability to maintain shapes), and we used those methods to identify the trade-offs associated with matrix formulation, printing speed, and acoustic pressure.