Daryl W. Yee | Searcharxiv

arXiv2026

Magnetically Responsive Microprintable Soft Nanocomposites with Tunable Nanoparticle Loading

Magnetic remote actuation of soft materials is attractive for applications such as transforming materials and medical robots. However, due to manufacturing limitations, microscale magnetoactive devices are scarce -- light-based additive manufacturing methods, despite achieving microscale resolution, struggle with particle-induced light scattering. Moreover, large hard-magnetic microparticles restrict ultimate feature sizes, and deformation of soft-magnetic nanoparticle composites requires impractically high loading and field gradients. Among successfully fabricated microscale soft-magnetic composites, limited control over particle loading, distribution, and matrix-phase stiffness has hindered their functionality. Here, we combine two-photon polymerization with iron oxide nanoparticle coprecipitation to fabricate 3D-printed microscale nanocomposites with spatially tunable nanoparticle distribution. We control nanoparticle content by locally modulating the two-photon dose, imbuing parts with varied magnetic functionality and achieving millimeter-scale elastic deformations, demonstrated by a soft robotic gripper and a bistable bit register and sensor. Our approach enables precise control of mechanical and magnetic properties towards microscale metamaterial and robotics applications.

cond-mat.soft↗

arXiv2022

Chemically-adhesive particles form stronger and stiffer magnetorheological fluids

Magnetorheological fluids (MRF) are suspensions of magnetic particles that solidify in the presence of magnetic fields due to the particles forming chains along field lines. The magnetic forces between particles dominate the solidification process and determine the yield stress of the material. Here, we investigate how reversible chemical links between particles influence MRF yield stress and stiffness through rheological testing in flow and oscillation mode. First, we functionalize particles with phosphonate groups that are expected to link through hydrogen bonding and find that this MRF exhibits up to 40% higher yield stress and 100% higher stiffness than an MRF composed of unfunctionalized particles. To explain this, we model the chemical attraction as an adhesion that supplements dipole-dipole interactions between particles. Interestingly, we find that the increase in yield stress is largest for dilute suspensions that are expected to solidify into isolated chains, while the proportional increase in yield stress is less for MRF with higher concentrations. This is explained by the higher concentration MRF forming a body-centered tetragonal (BCT) lattice in which interparticle adhesion forces are no longer aligned with the field. To explore the possibility of dynamically tuning interparticle interactions, we functionalize particles with polystyrene polymers with thymine terminal groups that will only exhibit interparticle hydrogen bonding in the presence of a linking molecule, namely melamine. We find that MRF formed with these particles also exhibit up to a 40% increase in yield stress and ~100% increase in stiffness, but only in the presence of melamine. In addition to confirming the role of hydrogen bonding in increasing MRF performance, these results highlight the possibility of dynamically tuning MRF performance using magnetic fields and chemical modifications.

cond-mat.soft↗