(182h) Moving Past Simple Shapes: Engineered Active Particle Spinners and Motors Powered By AC Electric Fields

Authors: 
Shields, C. W. IV, Duke University
Han, K., NC State University
Ma, F., NC State University
Velev, O. D., North Carolina State University
Active particles have gained tremendous attention in recent years due to their ability to harvest energy and autonomously power their movement, organization and reconfiguration. Ranging from molecular motors on the nanoscale to living organisms on the macroscale, active particles exist outside of equilibrium to convert energy into motion. The underlying mechanism driving their movement is in their design, as they asymmetrically draw and expel energy, thus creating local gradients of force for propulsion. While nature provides abundant examples of active particles that display highly advanced locomotive behaviors, progress in the lab has been limited by constraints in particle fabrication, such that most active particles developed insofar are simple Janus spheres. This bottleneck has restricted the potential for realizing new types of active particles with advanced properties for executing complex and intricate tasks. In this talk, we will show that the design and movement of active particles can be advanced through leveraging concepts in monolithic fabrication. We will show that a rich variety of particle designs with complex geometries (i.e., well-defined, non-spherical shapes) and polarizabilities can be achieved by top-down approaches (e.g., multi-layered lithography and metal evaporation). This results in the formation of millions of monodisperse, polymeric particles comprising a rich variety of shapes and metallic patches that give rise to a number of interesting and programmable field-particle and particle-particle interactions. Inspired by natural systems, we will show how this new class of “engineered active particles” can be designed in a variety of ways to swim, spin and freeze/melt on demand and in a tunable fashion. We will focus on the influence of shape and polarizability on the motile responses of the particles in an applied AC electric field. We will also investigate the collective behaviors of some of these particles, and we will provide descriptive physical explanations for their locomotion based on the interplay and coupling of electrohydrodynamic flows and induced charged electro-osmotic flows. Finally, building off of this understanding, we will show how the responses of the engineered particles can be enhanced or more finely controlled by leveraging the metallic patches along specific regions of the particles. Together, this work may provide a foundation for the next generation of active particles with engineered properties to execute a wide range of tasks, including remotely powered vehicles for targeted drug delivery, reconfiguring particle assemblies for microsurgical devices and swarms of particles for the next generation of self-healing materials.