Accurate Rheological Characterization of Highly-Filled Direct-Ink Write Pastes

Direct-ink write is an additive manufacturing technique that enables the creation of reproducible and complex hardware by depositing a viscous, shear-thinning liquid onto a substrate in a custom-pattern via extrusion through a syringe. The rheology of these inks is tailored through the addition of various filler materials. To successfully print highly-filled inks, we need to understand the effect of filler morphology, size, loading, and packing fraction on the ink rheology and corresponding printability. More importantly, characterization methods that accurately capture the ink’s rheological properties that correlate to resin printability is imperative. Various filler particles and volume loadings of particles were dispersed in Polydimethylsiloxane (PDMS, Sylgard® 182) to investigate the change in zero-shear viscosity, shear- thinning behavior, and plateau modulus. Comparisons between capillary rheometer measurements versus parallel plate rheometer measurements were made. The extrusion force was measured at several volume loadings determine the highest attainable volume loading for printable resins as a function of different filler morphologies. The goal of this work is to understand effects of filler morphology on ink printability while determining adequate characterization techniques that accurately capture the rheological behavior.<br/><br/><br/>Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.