Magnetic field-induced particle assembly and jamming

Ferromagnetic materials possess the ability to undergo magnetization in the presence of an external magnetic field and exhibit rapid responsiveness to magnetic field stimuli, rendering them highly suitable as carriers for stimuli-responsive materials. Furthermore, the assembly of ferromagnetic particles under the influence of a magnetic field allows for the design of assembled superstructures with diverse properties, enabling the fulfillment of specific application requirements. In this thesis, ferromagnetic cobalt (Co) and nickel (Ni) particles with various surface roughness were synthesized utilizing the polyol method. These particles were employed as building blocks for magnetic fieldinduced assembly, resulting in the formation of assembled superstructures with distinct properties. The unique characteristics of these superstructures were systematically characterized, followed by an exploration of their potential applications. Publication I utilizes a relatively smooth-surfaced ferromagnetic Co particles as building blocks enabled the assembly of weakly jammed superstructures under the influence of a magnetic field. The shape of these assembled superstructures could be controlled by adjusting the magnetic field strength, imparting tunable sensitivity in response to pressure stimuli. Publication II employs ferromagnetic Ni particles with comparatively rougher surfaces as building blocks, the heightened interparticle friction reduced the critical packing density required for achieving jamming. Consequently, strongly jammed superstructures were formed under the influence of a magnetic field. The pronounced jamming effect induced structural memory in the assembled superstructures, enabling tunable of jamming through magnetic field application kinetics and ultimately yielding broad tunability in response to stimuli. Publication III demonstrates the transfer of jamming-induced structural memory to electrical signals, which could be further transformed into visible light signals. Additionally, pulsed magnetic fields were employed to modulate the system's responsiveness.