Aging Behavior Of Wettability Of Plasma Modified Polyethylene

Polyethylene(PE). samples were modified by oxygen radio frequency(RF) capacitively coupled plasma(CCP), and the aging behavior of their wettability were researched. Surface morphology, composition, and wettability of the plasma modified PE samples were characterized by static contact angle, attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and 3D profile, respectively. After 5 hours of aging, the PE samples modified by 25 W for 5 minutes exhibited a slightly hydrophilic loss. The macroscopic surface morphology of the post-aged PE samples preserved no obvious change compared with that of the original samples, but the micro-structures and composition of the surfaces changed such that the calcium carbonate filler particles decreased and micro-ravines developed on the modified surfaces.A new aging effect on wettability was observed for the PE samples modified by CCP 200 W plasma for 5 minutes. The contact angle of the post-aged PE samples kept on increasing with the aging time, up to a superhydrophobic value of 150.5°for 5 hours. The surface morphology of the post-aged PE samples exhibited a remarkable change in surface roughness to a value of 187 nm. The 2D profiles showed the deep ravine-like etching trace on micrometer scale. The higher-density RF plasma texturing for a long time induced the formation of micro/nanostructure surface with micro-ravines and nano-islands on the PE samples. A lot of the oxygen-containing functional groups remained on the modified PE surfaces, although the aging processes aroused a hydrophobic recovery. The oxygen containing functional groups could induce the attractive force to water droplets and lead to the high adhesion on the post-aged PE surfaces.Aging temperature plays a significant role in the wettability of the post-aged PE samples. The aging process in air at the room temperature of 20℃induced the PE samples modified by CCP 200 W for 5 minutes to exhibit a hydrophobic over-recovery. The contact angle of the post-aged PE samples were higher than those of the original PE samples. The aging process in air at an aging temperature of 60℃showed a more remarkable change on wettability. The PE samples quickly turned superhydrophobic after only 1 hour of aging. When the aging temperature was 90℃, the PE samples showed superhydrophobic even in just 0.5 hr. The PE samples modified by CCP 200 W for 1 minute also exhibited a trend of the contact angle increasing with the higher aging temperature. The PE samples modified by CCP 200 W plasma for 10 minutes, after the aging processes in air at the aging temperatures of 20℃,60°C and 90℃, exhibited hydrophobic over-recovery, generally. Under an aging temperature of 20℃, the samples turned superhydrophobic after 5 hours of aging. When the aging temperature increased to 60℃and 90℃, respectively, the samples turned superhydrophobic after the same 0.5 hours of aging.