(379e) Magnetic Janus Particle Chain Length's Influence on Assembly Rate

When placed in a uniform magnetic field, magnetic Janus particles assemble into chains aligned with the magnetic field direction. The rate of this assembly process can be measured using optical microscopy. Comparison of experimental data and theory shows that the assembly rate is determined by two driving forces: particle diffusive forces and dipole-dipole forces of the chains. The diffusive forces of longer chains decrease their aggregation rates, but their stronger magnetic dipoles increase their aggregation rates. A model balancing these two facts by describing a “capture radius”, which increases with chain length, is used to predict assembly rates of each event type. Event types designate the size of the chains that are aggregating, e.g. singlet-singlet, singlet-doublet, etc. The assembly rate of each aggregation event type is determined by extracting Smoluchowski coagulation equation rate kernels from empirically observed concentration profiles of the individual chain types. These empirically determined rate kernels verify the theoretical model used to predict chain aggregation rates.