(363d) Dynamic Magnetochromatic Response of Concentrated Suspensions of Janus Particles

The promise of Janus particles as bulk additives for responsive complex fluids has been limited by the inability to scale up Janus particle functionalization. Particles having the high fidelity and monodispersity in both size and surface functionalization are fabricated utilizing particle monolayer formation and physical vapor deposition (PVD). Using Automated Langmuir Blodgett deposition, particle monolayers are fabricated on roll-to-roll substrates at meter per minute rates, overcoming the typical rate-limiting step for functionalization. Light transmittance of suspensions of Janus particles ranging from 1 - 50 microns in diameter subjected to both uniform and non-uniform oscillatory magnetic fields is measured. While larger Janus particles have faster response due to a larger magnetic force and slower relaxation due to Brownian rotation, smaller particles assembled into chains of particles give a significantly larger change in contrast due to their larger change in projected area along the light path. Their combined gravity-driven motion gives even more complexity to their orientation response. Janus particles dispersed in thermoreversible yield stress fluids also results in hysteresis response that suggests new modes of engineering of magnetically responsive complex fluids.