Light-induced Convective Segregation of Different Sized Particles

By heating an aqueous solution of gold nanoparticles by light, this solution and the suspended microparticles can be driven to flow within the confines of a microchamber. The convective flows are generated by thermal buoyancy effects and can be controlled by varying the intensity of imposed light and the concentration of the nanoparticles in the solution. Using computer simulations, we focus on a microchamber that is inclined at an angle with respect to the horizontal direction and demonstrate that the thermally-driven convective flows in this chamber can be harnessed to separate micrometer-sized particles along the bottom, inclined wall. A competition between the drag force imposed by the fluid flows and forces from gravity acting on the different sized particles gives rise to this particle separation. Furthermore, we show that the magnitude of the separation between the different particles increases with the increase of the inclined angle and the relative difference in the particle sizes. The separation of particles can also be tuned by changing the intensity of light. Our simulation results are supported by experimental observations. The behavior of the systems is highly robust and controllable and thus allows it to be used to a wide range of particle sorting applications.