Magnetophoretic Assembly of Anisotropic Colloids for Spatial Control of Reinforcement in Composites

Anisotropic particles have attracted interest for decades and have been studied for many aspects, ranging from fundamental phase behavior to photonic properties. In addition, magnetic fields have been heavily used for external manipulation of colloidal particles for separation, for assembly, and even for photonic applications. Here we use magnetic field microgradients established in a paramagnetic fluid to act as templates for the assembly of both nonmagnetic and magnetic anisotropic colloidal particles. We embed the assembled structure in a polymer matrix in order to obtain a composite where the spatial distribution of the reinforcing particles are preprogrammed. By using a mixture of paramagnetic and diamagnetic particles with different mechanical strengths, a periodical modulation of reinforcement by the variation of the particle type at different locations is achieved. Furthermore, we introduce a similar method for assembly of paramagnetic particles, where we use magnetic gradients of permanent magnet arrays to obtain field gradients and modulate spatially the particle concentration, and thus reinforcement, through the macroscopic samples in three dimensions.