Hydrodynamic flux-induced clustering of Janus particles in optical potential

Self-organisation is one of the most important strategies used by many biological systems, such as bacteria growth colonies, for the development of functional and complex patterned structures. Biological systems inspired self-organisation offers opportunities to simplify processes and to develop next generation materials and devices for molecular electronics, photonics and nanotechnology. The ability of organisation is mainly driven by the mutual interactions of the individual components and highly mediated by the environment features. In this work, we demonstrate experimentally that a system of Janus particles (half gold coated silica particles) experiences an unusual clustering in presence of a smooth Gaussian optical potential and an immediate release when the optical potential is switched off. Through numerical simulations we show that the key ingredient of the underlying mechanism is the existence of a hydrodynamic flow induced by a temperature gradient generated by the light absorption of the Janus particles. The proposed model is further applied to the case of non-Janus particles (non-coated silica particles) and of mixed Janus and non-Janus particles and well agrees with experiments in both cases.