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Abstract Direct ink writing (DIW) process is a facile additive manufacturing technology to fabricate three-dimensional (3D) objects with various materials. Its versatility has attracted considerable interest in academia and industry in recent years. As such, upsurging endeavors are invested in advancing the ink flow behaviors in order to optimize the process resolution and the printing quality. However, so far, the physical phenomena during the DIW process are not revealed in detail, leaving a research gap between the physical experiments and its underlying theories. Here, we present a comprehensive analytical study of non-Newtonian ink flow behavior during the DIW process. Different syringe-nozzle geometries are modeled for the comparative case studies. By using the computational fluid dynamics (CFD) simulation method, we reveal the shear-thinning property during the ink extrusion process. Besides, we study the viscosity, shear stress, and velocity fields, and analyze the advantages and drawbacks of each syringe-nozzle model. On the basis of these investigations and analyses, we propose an improved syringe-nozzle geometry for stable extrusion and high printing quality. A set of DIW printing experiments and rheological characterizations are carried out to verify the simulation studies. The results developed in this work offer an in-depth understanding of the ink flow behavior in the DIW process, providing valuable guidelines for optimizing the physical DIW configuration toward high-resolution printing and, consequently, improving the performance of DIW-printed objects.
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This content will become publicly available on October 1, 2026
Effects of Electrostatic Force on Conducting Polymer Jets in Electric Field-Assisted Direct Ink Writing
Abstract 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).
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- Award ID(s):
- 2224749
- PAR ID:
- 10643591
- Publisher / Repository:
- ASME
- Date Published:
- Journal Name:
- Journal of Manufacturing Science and Engineering
- Volume:
- 147
- Issue:
- 10
- ISSN:
- 1087-1357
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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