Two-step ion beam treatment for superhydrophilic fluorinated polymers

Plasma treatment is a widely used simple and ecofriendly method to improve the surface wettability of polymers. However, this is challenging for fluorinated polymers because of their robust CF bonds with low surface energies. Here, we demonstrated a simple approach, involving Ar-H-2 and O-2-H-2 two-step ion beam treatments, to achieve superhydrophilic fluorinated polymer surfaces. The effects of surface roughness and chemical composition on the water contact angle (WCA) were studied using X-ray photoelectron spectroscopy, scanning electron microscopy, and atomic force microscopy. After the single H-2 ion beam treatment on fluorinated ethylene propylene films, the WCA decreased from 110.2 degrees to 35.2 degrees due to defluorination and oxidation effects. However, the H-2 ion beam treatment alone has a limited effect on the root-mean-square (RMS) roughness, which hinders achieving superhydrophilicity. In contrast, the WCA significantly decreased to 1.3 degrees and 1.2 degrees, respectively after the Ar-H-2 and O-2-H-2 two-step ion beam treatments. Although the chemical composition after these treatments was similar to that after the single H-2 ion beam treatment, the RMS roughness increased upon the Ar and O-2 ion beam treatments because of the formation of nanostructures. Our results show that nanostructures with abundant polar oxygen bonds are required to obtain superhydrophilic surfaces in fluorinated polymers.