Thermophoretic nanomotors: towards 3D active fluids

In nature, living systems are driven from the bottom up. For example, molecular motors act collectively to enable cell motion and functionality despite a riotous environment induced by thermal fluctuations. Understanding how to generate work at small scale with artificial systems is now a fundamental research objective. To this end, we study the non-equilibrium dynamics of synthetic nanomotors self-propelled by thermophoresis. We activate them by laser-induced photothermal heating. We use confocal microscopy and nano-optical correlation techniques to probe their dynamics. We quantify collective heating and convective effects, enabling us to faithfully extract the active component from the measured dynamics. We demonstrate self-thermophoric propulsion at speeds up to 200µm/s, set by the light intensity. Our work further highlights the ability of our nanomotors to form 3D active baths, with potential to generate work at larger scale.