Water Droplet Impacting On Superhydrophobic Polyethylene Surfaces By Plasma Nanotexturing

Polyethylene samples are modified by oxygen and C4F8 radio frequency (RF) capacitively coupled plasma, the nanotexture of PE samples are presented by transferring the oxygen plasma treatment time. Surface morphology, functional groups, wettabiliby and drop impact property of the plasma modified PE samples are characterized by scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, contact angle measurement and high-speed camera. Surface roughness and aspect ratio increases with the increasing oxygen plasma treatment time. The widely stretch vibration peak of fluorine-containing groups at 950-1400cm-1 can be observed from the modified samples, the intensity of the peak retains stable with the increasing oxygen plasma etching time. Deposited 1 minute by C4F8 plasma, the water contact angle of modified substrate increases from 150.4 to 155.1 degree, the oil contact angle from 112.2 to 136.7 degree, the hysteresis decreased from 5.2 to 1.6 degree more than 5 minutes oxygen plasma eching, water sliding angle decreases from 59.3 to 3.2 degree and oil sliding angle from 5.8 to 0.9 degree, respectively with the increasing oxygen plasma treatment time from 1 minute to 60 minutes, which represents that hydrophobic property of the samples keep better with the increasing plasma treatment time. The result of droplet impact on treated surface can be analyzed that coefficient restitution keeps constant highly when We=1, decreases exponentially with the increasing We during We=5-30, and decreases faster when We more than 30. Increasing the We, the volume of secondary droplet which has extreme kinetic energy split by droplet is larger, and the more loss of energy are dissipated. The contact diameter of droplet with proceeding time during impact process are investigated, surface treated by oxygen plasma for 10,20 and 45 minutes, the critical Weber number presents 16,19 and 58 respectively, the 60 minutes treated surface shows splash phenomenon instead of stick on it even droplet impact behavior which the Weber number is more than 130. The treated surface has a high aspect ratio nanowire structure keeps the stable superhydrophobic property.