Propulsion and Assembly of Microparticles in External Fields

Colloidal particles are emerging as models for understanding the governing principles of assembly and non-equilibrium response of advanced materials. Our work focuses on understanding the universal principles governing the structure and dynamics of matter using colloids as model building blocks.  In this talk, I will present our work on the use of external fields to direct the assembly and spatial migration of colloids. First, I will introduce the principles of controlling and directing motion of metal-dielectric patchy colloids using external electric field. The electric field drives a local force imbalance around the metal patched particle, resulting into its direction motion. I will demonstrate how coupling of translation and rotational component of the energy enables programming helical motion in spherical colloids and provides an alternative mode of navigating through complex cross-linked matrices. Secondly, I will introduce our recent work which uncovers the dual nature of ferrofluids, particulate and continuous, to design a colloidal platform that couples competitive interactions with non-equilibrium dynamics. Using a binary suspension of microspheres in ferrofluid, we describe cyclical order-disorder-order transitions, and we access dynamic cluster states. I will show that crystal and fluid states represent two extremes in the competition between attraction and repulsion, while arrangement into clusters is a pseudo-equilibrium only observed from the true balance of interaction forces. Our findings establish a platform for experimental modeling of living matter with tunable competition between equilibrium and non-equilibrium forces.