Design principles in continuous inkjet electrohydrodynamic printing from discretized modeling and image analysis

Abstract

Electrohydrodynamic jet printing is a low cost, non-contact, direct-write and efficient process in obtaining high resolution prints for micro and nanofabrication. In electrically driven jets, the whipping motion, in particular, will lead to uncontrolled deposition of the jet in the printing process. In this work, we study the onset of the whipping motion at different applied voltage and nozzle to substrate distances for three different fluids. The model fluids for the study are chosen based on the viscoelasticity and electrical conductivity properties: i) polyisobutylene in polybutene (low conductivity and high viscoelasticity), ii) silver ink (high conductivity and low viscoelasticity), and iii) polyethylene oxide in water (high conductivity and high viscoelasticity). The radius profile of the jet and the onset of the whipping motion are obtained from the bead-spring model (simulations) and favorably compared with the high-speed images of the experiments. The onset position of whipping motion, and thus maximum stable jet length for electrohydrodynamic printing is obtained at different electric field conditions, and the trendline from the plot can be used as a guideline to design the printing length. In addition, a general correlation between electrostatic force parameter and Péclet number for electric field is obtained for all three model fluids when the electric field in the Debye length of the jet and convection length along the stable jet are applied in those dimensionless parameters. The correlation can be used as a predictive tool to obtain the stable jet length, which in turn can be used to set up the printing distance based on the printing conditions and printing solution.