Electrostatic Orientation of Optically Asymmetric Janus Particles

Janus micro- and nanoparticles, featuring unique dual-interface designs, are at the forefront of rapidly advancing fields such as optics, medicine, and chemistry. Accessible control over the position and orientation of Janus particles within a cluster is crucial for unlocking versatile applications, including targeted drug delivery, self-assembly, micro- and nanomotors, and asymmetric imaging. Nevertheless, precise mechanical manipulation of Janus particles remains a significant practical challenge across these fields. The current predominant methods, based on fluid flow, thermal gradients, or chemical reactions, have their precision and applicability limited by the properties of their background fluids. Therefore, this study proposes electrostatics to deliberately control the local orientation of optically asymmetric Janus particles (spherical and matchstick-like hybrid metal-dielectric objects) within a cluster to overcome the aforementioned restraints. We introduce a sophisticated multiphysics platform and employ it to explore and unveil the infrastructural physics behind the mechanical behavior of the particles when subjected to electrostatic stimuli in an ionic environment. We investigate how different deterministic and stochastic variables affect the particles' short- and long-term responses. By judicious engineering of amplitude, direction, and polarization of the external excitation, we demonstrate that the particles tend to undergo the desired rotational motion and converge to favorable orientations. The functionality of our approach is showcased in the context of an asymmetric imaging system based on optically asymmetric Janus particles. Our findings suggest a viable platform for adequate mechanical manipulation of Janus particles and pave the way for enabling numerous state-of-the-art applications in various fields.