Fractal Characteristics of Disordered Microstructure on the Laser-Textured Silicone Rubber Surface in Wettability Transition

In this paper, hydrophobic/superhydrophobic silicone rubber surfaces with disordered structures were prepared with a nanosecond laser. The fractal characteristic of the surfaces was also investigated. The results show that the fractal structures on the processed silicone rubber surface can roughly reflect the increasing trend of its hydrophobicity. More specifically, the air content in the liquid-solid contact area was found to be related to the surface superhydrophobicity. The solid fraction of superhydrophobic surfaces at close to 0.22 produced with different laser pulse widths can be used to identify whether such surfaces are in the superhydrophobic state after the laser treatment. In addition, the fractal parameters and gas/solid fraction could be used to predict the contact angles of surfaces in Wenzel and Cassie-Baxter states based on the fractal wetting equations. However, it is noted that with the increase of the laser fluence, the silicone rubber surfaces enter into a mixed state where the Wenzel and Cassie-Baxter states coexist. This paper provides a new method to characterize the wettability of the surfaces with the disordered microstructures.