Superwetting antibacterial copper oxide nanoflake foil substrates generated by thermal oxidation

A facile one-step method of roughened copper foils of 0.0076 ​mm thickness heated on the open flame for 15 ​s produced superhydrophilic surfaces that exhibited superwetting at average radial growths of 10.8 ​mm/s following drop dispensation. Superhydrophilicity was found to deteriorate over time and XRD analysis ruled out compositional change as the cause of this behaviour. Instead, SEM imaging revealed wrinkled 20–30 ​nm-thick nanoflakes that were predominantly stretched out initially to engender superwetting properties via Wenzel wetting. These extended microstructures folded up with time due to relaxation of the residual stresses from the thermal oxidation process, resulting in temporal reduction in superhydrophilicity, which can be restored by reapplying thermal oxidation. The impingement of air with 80 psi pressure on the substrate also caused similar deterioration. The superwetting characteristic also endowed these substrates with anti-bacterial properties where a 56% reduction in bacteria count with Staphylococcus epidermidis was found.