Effects of surface oxides and nanostructures on the spontaneous wettability transition of laser-textured copper surfaces

Highlights: • Cu wicks spontaneously become superhydrophobic due to VOC adsorption. • Surface oxides enhance surface hydrophilicity and delay wettability transition. • Capillary pumping performance deteriorates after wettability transition. • The adsorbed organics can be partly removed under continuous boiling. • Surface nanoparticles remarkably enhance the stability of surface hydrophilicity. The spontaneous wettability transition of metal and metal oxide surfaces caused by the adsorption of airborne volatile organic compounds (VOCs) has been frequently reported. In this study, we examine the effects of surface oxides and nanostructures on the wettability transition as well as the stability of the acquired hydrophobicity under boiling conditions. The results demonstrate that the presence of a thin oxide layer enhances the surface hydrophilicity and slightly delays the spontaneous wettability transition. Short-term exposure of the prepared samples to atmospheric air does not affect the boiling performance, but long-term exposure results in a dramatic decrease of the critical heat flux (CHF). The adsorped organics can be partly removed under continuous boiling, resulting in the partly recovery of the CHF after the first boiling test as well as the partly recovery of the surface hydrophilicity after the entire boiling tests. The presence of abundant surface oxide nanoparticles can markedly enhance the stability of the original hydrophilicity, which may result from the huge specific surface area of the nanostructured surfaces. Our results help a better understanding of the spontaneous wettability transition phenomenon, benefiting the manufacturing of high-performance heat transfer devices.