Electrohydrodynamic (EHD) printing of microparticle streams for additive manufacturing

Abstract

Electrohydrodynamic (EHD) printing can be used to fabricate high resolution (~100 nm) features at high rates (~10 kHz), and is compatible with a wide range of materials. However, conventional EHD printing techniques focus only on homogeneously dispersed functional inks, including nanoparticulate materials, molecular and polymers. This thesis explores EHD printing of liquids containing microparticles. For printing, liquids containing microparticles with a diameter of ~1-10 pm are prepared, which sediment upon loading into the capillary tip. A single-tip EHD apparatus enabling pulsed delivery of kilovolt signals, high speed imaging, and measurement of charge transfer to the substrate has been constructed. Using this apparatus, it is shown that pulsed voltage signals can cause printing of liquid droplets, streams, and aggregates containing microparticles, at rates of ~10 kHz. Upon evaporation of the liquid, the particles organize into clusters that, depending on the deposition conditions, may form continuous lines or regularly spaced aggregates. By first-order modeling of the forces exerted on the particles, it is concluded that the amount of colloidal material ejected from the capillary is influenced by the packing of the particles within the meniscus, their size, the strength of electrostatic and Van der Waals interactions, and other factors. Future work should focus on the design of the colloidal solution and EHD parameters to enable controlled and consistent ejection of particles, and improvement of the accuracy of deposition. This process therefore is attractive for additive manufacturing of composite materials by direct deposition of microparticles.