Abstract
Nature shows many examples of surfaces with extraordinary wettability, which can often be associated with particular air-trapping surface patterns. Here, robust non-wetting surfaces have been created by femtosecond laser ablation of polytetrafluoroethylene (PTFE). The laser-created surface structure resembles a forest of entangled fibers, which support structural superhydrophobicity even when the surface chemistry is changed by gold coating. SEM analysis showed that the degree of entanglement of hairs and the depth of the forest pattern correlates positively with accumulated laser fluence and can thus be influenced by altering various laser process parameters. The resulting fibrous surfaces exhibit a tremendous decrease in wettability compared to smooth PTFE surfaces; droplets impacting the virgin or gold coated PTFE forest do not wet the surface but bounce off. Exploratory bioadhesion experiments showed that the surfaces are truly air-trapping and do not support cell adhesion. Therewith, the created surfaces successfully mimic biological surfaces such as insect wings with robust anti-wetting behavior and potential for antiadhesive applications. In addition, the fabrication can be carried out in one process step, and our results clearly show the insensitivity of the resulting non-wetting behavior to variations in the process parameters, both of which make it a strong candidate for industrial applications.
Highlights
As an old Chinese proverb goes, a lotus lives in the silt but not imbrued
PTFE surfaces have been micromachined with the intention to create surface structures that robustly support air-trapping Cassie-wetting
We have shown that a PTFE surface after raster scanning under a 800 nm femtosecond laser beam shows a fibrous surface structure, which is reminiscent of the surface features found on certain insect wings and plant surfaces
Summary
As an old Chinese proverb goes, a lotus lives in the silt but not imbrued. Dirt particles are picked up by water droplets freely rolling over lotus leaves. Nature has optimized plant and animal species for their respective living environments, such as the surfaces of plants [1,2], the wings [3,4,5] and legs of insects [6,7], or the skin of marine animals [8] and reptiles [9] All of these exhibit prime examples for surfaces with specific functionalities, such as air-trapping, self-cleaning, anti-fouling and anti-bacterial characteristics. The fabrication of such surfaces is in many cases rather complicated, involving many process steps and demanding equipment that does not favor easy scale-up This project, inspired by natural superhydrophobic surfaces, had the particular goal to create a highly robust synthetic non-wetting surface through a relatively simple fabrication process for easy scaling-up and transfer to such industrial applications as outlined above. Larger surface areas of such structures are desired instead of multipulse craters to investigate the suitability of this machining process for industrial applications
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