Colloidal assembly under orthogonally applied electric and magnetic fields: chains, chiral clusters, and quasicrystals

Colloidal particles have been used either as model systems for materials science or as building blocks for making functional materials. Previous work primarily focused on assembling colloids under a single external field, where controlling particle-particle interaction is often limited. This talk will present results under a combination of electric and magnetic fields. When these two fields are orthogonally applied, we can independently tune the nature, magnitude, direction, and effective range of interparticle interactions. As a result, we can obtain well-aligned, highly dense, but individually separated linear chains at intermediate particle concentrations for isotropic microspheres or chiral colloidal clusters with tunable handedness when the building blocks are anisotropic colloidal dimers. Furthermore, we will present our recent results of dodecagonal quasicrystals assembled from one-component microspheres. We will report our experimental observations, underlying mechanisms, and tunability of the assembled structures. In addition, we have also performed Monte Carlo and Brownian Dynamics simulations in which the electric and magnetic dipolar interactions and electrohydrodynamic interactions are involved to gain a more fundamental understanding of our experimental results. Our method provides a convenient route for producing complex and hierarchical structures that are challenging to make using one field only.