On the Stability of Electrohydrodynamic Jet Printing Using Poly(ethylene oxide) Solvent-Based Inks

Abstract

Electrohydrodynamic (EHD) jet printing of solvent-based inks or melts allows for the producing of polymeric fiber-based two- and three-dimensional structures with sub-micrometer features, with or without conductive nanoparticles or functional materials. While solvent-based inks possess great material versatility, the stability of the EHD jetting process using such inks remains a major challenge that must be overcome before this technology can be deployed beyond research laboratories. Herein, we study the parameters that affect the stability of the EHD jet printing of polyethylene oxide (PEO) patterns using solvent-based inks. To gain insights into the evolution of the printing process, we simultaneously monitor the drop size, the jet ejection point, and the jet speed, determined by superimposing a periodic electrostatic deflection. We observe printing instabilities to be associated with changes in drop size and composition and in the jet’s ejection point and speed, which are related to the evaporation of the solvent and the resulting drying of the drop surface. Thus, stabilizing the printing process and, particularly, the drop size and its surface composition require minimizing or controlling the solvent evaporation rate from the drop surface by using appropriate solvents and by controlling the printing ambient. For stable printing and improved jet stability, it is essential to use polymers with a high molecular weight and select solvents that slow down the surface drying of the droplets. Additionally, adjusting the needle voltages is crucial to prevent instabilities in the jet ejection mode. Although this study primarily utilized PEO, the general trends observed are applicable to other polymers that exhibit similar interactions between solvent and polymer.

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“…9 Higher viscosity (non-Newtonian) inks, on the other hand, have been shown to lead to more stable jets in the EHD process. 10 Given that EHD is a newer, less utilized technique, there is currently a very limited selection of commercial inks that have been designed or optimized for high-resolution EHD printing. The advantages of EHD printing also enable its use for precise fabrication in distinctive scenarios, such as manufacturing in space, where gravity is absent.…”

“…Additionally, such small nozzles are more difficult and costly to produce and tend to be more fragile and likely to clog during printing . Higher viscosity (non-Newtonian) inks, on the other hand, have been shown to lead to more stable jets in the EHD process . Given that EHD is a newer, less utilized technique, there is currently a very limited selection of commercial inks that have been designed or optimized for high-resolution EHD printing.…”