Synergistic Inclusion Effects of Hard Magnetic Nanorods on the Magnetomechanical Actuation of Soft Magnetic Microsphere-Based Polymer Composites

The magnetomechanical actuation of micropillars is developed for the contactless manipulation of miniaturized actuators and microtextured surfaces. Anisotropic geometry of micropillars can significantly enhance the magnetic actuation compared with their isotropic counterparts by directional stress distributions. However, this strategy is not viable for triangular micropillars owing to insufficient anisotropy. In this study, a significant improvement in the magnetic actuation of triangular micropillars using composite magnetic particles is reported. A minute and optimal amount of hard magnetic gamma-ferrite nanorods are hybridized with soft magnetic iron microspheres to generate synergistic effects of magnetic coupling and percolation phenomenon on the magnetic actuation of polymer composites. The addition of 1 wt% face-centered cubic-phased gamma-ferrite nanorods suppresses the magnetic coupling interference of body-centered cubic-phased iron microspheres. Furthermore, the nanorods reduce the percolation threshold by participating in the percolation of the microspheres. A systematic compositional study on the magnetization and magnetorheological properties reveals that the coupling effect dominates the percolation effect at a low magnetic field, whereas the percolation effect governs the magnetic actuation at a high magnetic field. This hybrid approach can help in designing material constituents for effective magnetic actuators and robotic systems that can sensitively respond to an external magnetic field. Soft magnetic microspheres and hard magnetic nanorods are hybridized to arouse magnetic couplings and structural percolation effects within polymer matrix. Synergy from two effects enables polymer/nanorod/microsphere composites to improve magnetization values and storage modulus. The micropillars of polymer/nanorod/microsphere composites exhibit enhanced magnetomechanical bending actuation, compared to that of polymer/microsphere, although cross section geometry is triangles, unfavorable for focusing stress.image

Automated summary

In this study, a significant improvement in the magnetic actuation of triangular micropillars using composite magnetic particles is reported. A minute and optimal amount of hard magnetic gamma-ferrite nanorods are hybridized with soft magnetic iron microspheres to generate synergistic effects of magnetic coupling and percolation phenomenon on the magnetic actuation of polymer composites. This hybrid approach can help in designing material constituents for effective magnetic actuators and robotic systems that can sensitively respond to an external magnetic field.