Bioinspired Further Enhanced Dry Adhesive by the Combined Effect of the Microstructure and Surface Free-Energy Increase.

Silicone elastomers are known for having low surface free energies generally leading to poor adhesive performances. This surface characteristic can be enhanced by plasma treatments. The microstructured silicone elastomer surfaces can demonstrate superior adhesive performance that is more than 10 times higher in terms of pull-off forces, compared to their unstructured counterpart. Here, we have demonstrated that the combination of these two methods further enhances adhesive performance, especially when the surfaces are biomimetic micro/nanopatterned with, e.g., beetle-inspired mushroom-shaped adhesive microstructure (MSAMS). The plasma treatment time and pressure parameters were varied for the unstructured and MSAMS poly(vinylsiloxane) surfaces to find optimum parameters for maximum adhesion performance. Air plasma treatment induced average adhesive enhancement forces up to 30% on the unstructured surface, but the MSAMS surface demonstrated an enhancement of adhesive forces up to 91% higher than that of an untreated, microstructured control, despite the plasma-treated surface area of the structured surface being only 50% of that of the unstructured surface. High-speed video-recordings of individual microstructures in contact with a glass surface shows that the origin of the adhesion enhancement is due to the special detachment mechanism of individual microstructures that allows sustaining a wider contact area at detachment. We believe that this integration of the plasma treatment with MSAMS suggests a versatile way of functionalization that can further advance the adhesive ability of low-surface-energy polymer surfaces.