Material Behavior of Magnetoresponsive Polymer Composites in Extrusion-Based Direct Writing

Abstract Direct writing (DW) is a key extrusion-based additive manufacturing (AM) technique for fabricating polymer-particle functional composites, widely used in biomedical, electronics, and energy storage applications. DW relies on controlled ink extrusion and deposition, where rheological properties play a crucial role in ensuring smooth flow, shape retention, and printing accuracy. Shear-thinning and viscoelastic behaviors are preferred, as they facilitate precise extrusion and structural integrity. However, low-viscosity and nonelastic inks pose challenges, leading to spreading, poor dimensional accuracy, and weak interlayer adhesion. To enhance control over such inks, external forces (electrical, acoustic, and magnetic fields) are integrated into DW systems. Among these, magnetic fields offer contactless control over particle orientation and ink rheology, enabling the fabrication of complex structures. The magnetorheological effect enhances viscoelasticity by forming directional magnetic particle clusters, improving deposition precision. However, nonmagnetic particles (e.g., silicon carbide (SiC)) disrupt magnetic chain formation, leading to issues like clogging, bulging, and discontinuities. This study examines the rheological behavior of polymer composites with varying nanoparticle concentrations in DW. The magnetorheological response of the composite plays an important role in controlling ink-wetting behavior and was analyzed under different magnetic field strengths. Results showed that Fe3O4 particles enhance elasticity, while SiC nanoparticles influence viscoelastic properties. Preliminary magnetowettability tests revealed an increased contact angle and smoother extrusion under a magnetic field, demonstrating improved deposition control. These findings emphasize the importance of magnetically controlled rheology in enhancing the precision and performance of DW-based AM processes.