Effects of O₂Plasma Treatment on the Hydrophilic/hydrophobic Contrast of Film Substrates

Abstract

We studied the effects of O 2 plasma on the hydrophilic/hydrophobic contrast of film substrates. PET (polyethylene terephthalate) and FEP (fluorinated ethylene propylene) films were treated by O 2 plasma, and the surface of the films was investigated using atomic force microscopy(AFM), X-ray photoelectron spectroscopy (XPS), and contact-angle and surface energy measurements. Surface energies were calculated from the measured contact angles between several solutions and the films based on the geometric mean and Lewis acid-base method. The contact angle of PET films treated by O 2 plasma decreased with increasing treatment time in water and surfactant solution, and surface energy increased with increasing polar component of surface tension of the film. In contrast, the contact angle of the O 2 plasma-treated FEP film decreased, and surface energy decreased with decreasing nonpolar component of surface tension of the film.

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“…Contrary to that, the FEP material showed no significant changes in the calculated polar component of the surface tension due to marginal changes in the measured water contact angles. As the latter was also observed by Kang 31 for short times of an O 2plasma-etching process, we expect that no oxygenated species were grafted on the surface.…”

Contribution of surface energy and roughness to the wettability of polyamide 6 and polypropylene film in the plasma-induced process

“…Plasma etching induces chain scission at the polymer surface, breaking the chemical bonds and removing a weak boundary layer of polymer chains, producing nano-textured surfaces. 10–12 The plasma etching process by itself has often been used to fabricate superhydrophilic surfaces, 6,13,14 and the enhanced wettability is generally attributed to the combined effect of surface oxidation and increased surface roughness. 13 However, the enhanced wettability obtained by O 2 plasma etching is not permanently maintained compared to that initially attained; a hydrophobic recovery is often encountered with time, through the reorientation of polar surface groups toward the bulk.…”

“…Efforts have been made to estimate the dispersive and polar components of surface energy for roughened surfaces with nano-scale features. 14,27 However, this approach is controversial because in this case the surface roughness additionally contributes to the wetting parameter, where the assumption of the Owens–Wendt model is not strictly met. 26 The roughened surface would rather follow the Wenzel or the Cassie–Baxter models, 25,28 where the roughness factors are considered.…”