A Quantitative Theory of Magnetic Janus Particle Assembly

Under a magnetic field, Janus particles with magnetic caps (magJP) assemble into 2D chains. These chains give the fluid they are immersed in interesting rheological properties. More specifically, the longer the chains, the greater the viscosity. The rate of the magJP assembly is dependent on the dipole strength of the particles and is studied in this project. Predicting and controlling the magJP assembly rate will enable the engineering of materials that have desirable properties.

We have carried out experiments that measure the assembly rate of the magJP chains. The particles are synthesized, confined to a 2D environment, placed in a magnetic field, and tracked as they assemble. Particle tracking software has been developed for the project, and has been used to collect information from the videos including: chain concentrations vs time, particle trajectories, and dipole-dipole interaction energy. The results are fit to the Smoluchowski coagulation equations to obtain rate constants for chain aggregation.

The talk will discuss the relevance of these rate equations. A theory is proposed for prediction of the magJP rate constants when varying: concentration, dipole strength, dipole shift, viscosity, and particle size. The theory is shown to predict the magJP rate constants and future experiments are proposed to further test the theory.