Photothermal Marangoni convection on nanostructured surfaces

In this study, we investigated the influence of nanoscale structures on the channel walls on photothermally induced Marangoni convection within a droplet. SiO₂nanocolumns with varying densities and heights were fabricated on an FeSi₂thin film with photothermal conversion properties, onto which a water droplet was placed. A laser was then used to irradiate the FeSi₂thin film, thereby heating the vicinity of the gas-liquid interface of the droplet. The resulting Marangoni flow in the droplet was visualized using tracer particles. Compared with flat films, nanostructured surfaces exhibited both faster onset and a higher magnitude of convection, with significant flow maintained even when the laser was distant from the gas-liquid interface. This enhancement was attributed to the capillary-driven replenishment of water in the nanocolumns and efficient heat transfer via phase change, which rapidly establishes a temperature gradient at the interface. Variations in nanocolumn height and density were found to affect the initial evaporation rate and convection response. These findings suggest that the surface nanostructure can efficiently modulate the temperature gradients on the droplet surface and enhance the Marangoni flow, which is valuable for microfluidic applications.