Synthesis of transparent superhydrophobic polyethylene surfaces

Abstract

Superhydrophobic surfaces, already present in the nature as observed with leaves of plants (lotus) or feathers of some birds, correspond to hydrophobic surface whose water contact angle is higher than 150°. Before running the synthesis of such surface, one must understand the corresponding phenomenon and define the pertinent characteristics. Most of the techniques already developed lead to surfaces with weak physical properties such as optical and mechanical ones. Here, the synthesis in dry medium (plasma) is proposed leading to stable and transparent polymeric superhydrophobic surfaces. Two routes are possible; the first one corresponds to the one-step synthesis (CF 4 plasma modification of low density polyethylene (LDPE)), the second one to the two steps (O 2 plasma treatment followed by CF 4 plasma onto LDPE). The plasma parameters are defined to optimize the degradation and/or the functionalization and the obtained surface structures are characterized. The O 2 plasma allows to create a variable roughness while CF 4 plasma emphasizes this roughness and creates the apolar layer. By the two-step treatments, several plasma parameters were found to elaborate stable transparent superhydrophobic surfaces with a controlled roughness and whose chemical structure is close to a Teflon-like structure. It has been shown that superhydrophobic surface can be obtained even with a low roughness, around 20 nm.