Plasma-Treated Superhydrophobic Polyethylene Surfaces: Fabrication, Wetting and Dewetting Properties

Superhydrophobic surfaces correspond to hydrophobic surfaces whose water contact angle is higher than 150 degrees. Two new routes involving plasma technique are proposed to prepare such surfaces: the first one is a one-step process (CF4 plasma modification of low density polyethylene), and the second involves two steps (O-2 plasma treatment followed by CF4 plasma treatment). The plasma parameters are defined to optimize the degradation and/or the functionalization. The O-2 plasma allows to create a variable roughness while CF4 plasma accentuates this roughness and creates a non-polar layer. With the two-step treatment, plasma parameters were found which produced superhydrophobic surfaces with a controlled roughness and whose chemical structure was close to a Teflon-like structure. The wetting and dewetting of these superhydrophobic surfaces are compared to those of only hydrophobic polyethylene. The behavior of surfaces, whether dry or prewetted with water vapor, is found to be different. The dewetting of the dried surface previously prewetted is found to be discontinuous, and slower than that of the dry one. This specific behavior is interpreted as a roughness effect on trapped water. However, its dewetting is still faster than that of the corresponding hydrophobic surface such as PTFE. (c) Koninklijke Brill NV, Leiden, 2009