Abstract
Active colloids are an emergent class of out-of-equilibrium materials demonstrating complex collective phases and tunable functionalities. Microscopic particles energized by external fields exhibit a plethora of fascinating collective phenomena, yet mechanisms of control and manipulation of active phases often remains lacking. Here we report the emergence of unconfined macroscopic vortices in a system of ferromagnetic rollers energized by a vertical alternating magnetic field and elucidate the complex nature of a magnetic roller-vortex interactions with inert scatterers. We demonstrate that active self-organized vortices have an ability to spontaneously switch the direction of rotation and move across the surface. We reveal the capability of certain non-active particles to pin the vortex and manipulate its dynamics. Building on our findings, we demonstrate the potential of magnetic roller vortices to effectively capture and transport inert particles at the microscale.
Highlights
Active colloids are an emergent class of out-of-equilibrium materials demonstrating complex collective phases and tunable functionalities
Out of equilibrium ensembles of colloidal particles powered by external energy input often demonstrate remarkable level of complexity when driven out of equilibrium
Active systems, composed of colloidal particles, transduce the energy stored in the environment or delivered by an external field into mechanical motion
Summary
Active colloids are an emergent class of out-of-equilibrium materials demonstrating complex collective phases and tunable functionalities. Active systems, composed of colloidal particles, transduce the energy stored in the environment or delivered by an external field into mechanical motion They represent a convenient platform that allows investigating in detail the onset of coherent motion and self-organization in out-of-equilibrium multi-particle ensembles. It is largely because of their controllability, size, diverse range of tunable interactions and the absence of complex biochemical factors obscuring studies in biological systems. An active roller vortex can spontaneously switch the direction of rotation We further use these self-assembled roller vortices to explore their complex interactions with inert scatterers and reveal the ability of passive particles with sizes above a certain limit to effectively trap the active vortex core and manipulate its dynamics. Our work provides new fundamental insights into behavior of a broad class of active systems where collective motion is caused by a fine interplay between rotational and translational degrees of freedom, and suggest new techniques of control and transport of active colloids in general
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