Effects of Electrostatic Force on Conducting Polymer Jets in Electric Field-Assisted Direct Ink Writing

The electronics industry is rapidly advancing toward the development of highly miniaturized sensors and circuits, driving an increasing demand for precise, localized manufacturing techniques. Extrusion-based additive manufacturing—particularly direct ink writing—has emerged as a promising method for fabricating microscale electronic components. Recent efforts have focused on producing fine-resolution structures capable of conformal deposition on complex or uneven surfaces. While prior studies have established theoretical models for the trajectory of non-conductive material jets under electric fields—demonstrating feasibility in printing high-resolution features—a theoretical framework for conductive ink behavior under similar conditions remains lacking. This study introduces a theoretical model to describe the behavior of conductive jet extrusion under varying electrostatic forces. The model is validated through high-speed physical and manufacturing experiments using poly(3,4-ethylene-dioxythiophene)-based ink. The results demonstrate that the application of an external electric field significantly broadens the printable window, enabling: (i) high-speed printing up to 1.7 m/s with successful deposition on rough textile substrates (average surface roughness Ra = 8 µm), and (ii) the formation of micro-sized lines with widths as small as ∼60% of the nozzle's inner diameter (e.g., 300 µm-wide lines printed using a 500 µm diameter nozzle).