Robust Hierarchical Porous PTFE Film Fabricated via Femtosecond Laser for Self-Cleaning Passive Cooling.

Passive cooling materials that spontaneously cool an object are promising choices for mitigating the global energy crisis. However, these cooling effects are usually weakened or lost when dust contaminates the surface structure, greatly restricting their applications. In this work, a robust hierarchical porous polytetrafluoroethylene (PTFE) film with coral-like micro/nanostructures is generated by a facile and efficient femtosecond laser ablation technique. Owing to its unique micro/nanostructures, the as-prepared surface exhibits an outstanding self-cleaning function for various liquids with ultralow adhesion. This self-cleaning characteristic enhances the durability of its passive cooling effect. It is demonstrated that the titanium (Ti) sheet covered with laser-ablated PTFE film can realize a maximum temperature decrease of 4 and 10 °C compared to the Ti sheet covered with pristine PTFE film and uncovered, respectively. This study reveals that femtosecond laser micromachining is a facile and feasible avenue to produce robust self-cleaning passive cooling devices.