Electrostatic Orientation of Optically Asymmetric\nJanus Particles

Janus micro- and\nnanoparticles, featuring unique dual-interface\ndesigns, are at the forefront of rapidly advancing fields such as\noptics, medicine, and chemistry. Accessible control over the position\nand orientation of Janus particles within a cluster is crucial for\nunlocking versatile applications, including targeted drug delivery,\nself-assembly, micro- and nanomotors, and asymmetric imaging. Nevertheless,\nprecise mechanical manipulation of Janus particles remains a significant\npractical challenge across these fields. The current predominant methods,\nbased on fluid flow, thermal gradients, or chemical reactions, have\ntheir precision and applicability limited by the properties of their\nbackground fluids. Therefore, this study proposes electrostatics to\ndeliberately control the local orientation of optically asymmetric\nJanus particles (spherical and matchstick-like hybrid metal–dielectric\nobjects) within a cluster to overcome the aforementioned restraints.\nWe introduce a sophisticated multiphysics platform and employ it to\nexplore and unveil the infrastructural physics behind the mechanical\nbehavior of the particles when subjected to electrostatic stimuli\nin an ionic environment. We investigate how different deterministic\nand stochastic variables affect the particles’ short- and long-term\nresponses. By judicious engineering of amplitude, direction, and polarization\nof the external excitation, we demonstrate that the particles tend\nto undergo the desired rotational motion and converge to favorable\norientations. The functionality of our approach is showcased in the\ncontext of an asymmetric imaging system based on optically asymmetric\nJanus particles. Our findings suggest a viable platform for adequate\nmechanical manipulation of Janus particles and pave the way for enabling\nnumerous state-of-the-art applications in various fields.