  Self-organisation is driven by the interactions between the individual
components of a system mediated by the environment, and is one of the most
important strategies used by many biological systems to develop complex and
functional structures. Furthermore, biologically-inspired self-organisation
offers opportunities to develop the next generation of materials and devices
for electronics, photonics and nanotechnology. In this work, we demonstrate
experimentally that a system of Janus particles (silica microspheres
half-coated with gold) aggregates into clusters in the presence of a Gaussian
optical potential and disaggregates when the optical potential is switched off.
We show that the underlying mechanism is the existence of a hydrodynamic flow
induced by a temperature gradient generated by the light absorption at the
metallic patches on the Janus particles. We also perform simulations, which
agree well with the experiments and whose results permit us to clarify the
underlying mechanism. The possibility of hydrodynamic-flux-induced reversible
clustering may have applications in the fields of drug delivery, cargo
transport, bioremediation and biopatterning.
