Rotating Dielectric-Plasmonic Janus Particles via Electrostatic Voltages to Enable Optical Functionalities

Janus particles, characterized by their dual-sided physical properties, play a pivotal role in fields like optics, medicine, and chemistry. Their inherent asymmetry gives rise to unique light-scattering properties crucial for developing a one-way cloud. Our research focuses on a dense ensemble of optically asymmetric Janus particles, including spherical and matchstick-like hybrid dielectric-plasmonic structures, which effectively act as a synthesized bulk medium with anisotropic optical characteristics. Such synthetic material results in an asymmetric smoke, creating a clear or obscured vision based on the viewing direction. However, achieving the necessary light-scattering asymmetry hinges on the precise orientation of these particles within the cluster. Various approaches have been implemented for the mechanical manipulation of Janus particles, including electromagnetic fields, mechanical waves, and fluid flow. Despite the effectiveness of current methods, the precise alignment of particles within a random array remains a significant challenge and an active area of research. In our study, we propose using electrostatics as an accessible and reliable method to meticulously orient optically asymmetric Janus particles within a dense cloud. Our findings show that by precisely engineering the amplitude, direction, and polarization of external excitation, we can effectively manipulate the final orientation of the particles in the smoke. This approach offers a unique perspective by creating stable steady states in the orientation space, enabling control over both the short- and long-term behaviors of the particles in the cluster. We demonstrate the effectiveness of our approach by applying it to a cluster of Janus particles, successfully realizing a one-way cloud to provide coded visibility. Our analysis confirms that our method can precisely align optically asymmetric particles, creating a cloud that manipulates vision based on the observation direction.<br/>We introduce and develop a sophisticated multiphysics platform that combines electrostatics and rigid body dynamics to concurrently predict the particles' electrostatic and mechanical responses when subjected to electrostatic stimuli in an ionic medium. We use this platform to investigate the impacts of various deterministic and stochastic variables on the transient and steady-state responses of the particles. Our findings show that engineering stable steady states in the orientation space can effectively align the particles within the cluster, even amidst thermal fluctuations. Additionally, our study reveals the effects of translational and rotational Brownian motions on the performance of the one-way cloud and details how to mitigate these negative impacts by enhancing deterministic electrostatic excitation. This work offers a robust model for manipulating micro- and nanoparticles and facilitates future applications, including directional light-scattering, targeted drug delivery, self-assembly, and autonomous swimmers.