Mechanisms of Oxygen Plasma Nanotexturing of Organic Polymer Surfaces: From Stable Super Hydrophilic to Super Hydrophobic Surfaces

Abstract

Plasma processing is used to fabricate super hydrophilic or super hydrophobic polymeric surfaces by means of O2 plasma etching of two organic polymers, namely, poly(methyl methacrylate) (PMMA) and poly(ether ether ketone) (PEEK); a C4F8 plasma deposition follows O2 plasma etching, if surface hydrophobization is desired. We demonstrate high aspect ratio pillars with height ranging from 16 nm to several micrometers depending on the processing time, and contact angle (CA) close to 0 degrees after O2-plasma treatment or CA of 153 degrees (with CA hysteresis lower than 5 degrees) after fluorocarbon deposition. Super hydrophobic surfaces are robust and stable in time; in addition, aging of super hydrophilic surfaces is significantly retarded because of the beneficial effect of the nanotextured topography. The mechanisms responsible for the plasma-induced PMMA and PEEK surface nanotexturing are unveiled through intelligent experiments involving intentional modification of the reactor wall material and X-ray photoelectron spectroscopy, which is also used to study the surface chemical modification in the plasma. We prove that control of plasma nanotexture can be achieved by carefully choosing the reactor wall material.

Oxygen and nitrogen plasma hydrophilization and hydrophobic recovery of polymers

“…Some groups have also investigated the aging behaviour of oxygen plasma treated PMMA surfaces for different periods of times. Both Schmalenberg et al 8 and Tsougeni et al 9,23 reported that the hydrophobic recovery begun almost immediately after relatively short exposure (30 s-5 min). On the other hand, longer treatments (20 min-60 min) were reported to make the surface superhydrophilic for several days.…”

“…[6][7][8][9]21,23,36 Several studies 9,21,23 have demonstrated that longer treatment times induce more hydrophilic surfaces. Similar results have been observed for higher plasma powers as compared with lower ones, 6 implicating that the higher the plasma dose the lower the measured contact angle.…”

“…[16][17][18] Typically, polymer surfaces exposed to oxygen or nitrogen plasmas become more hydrophilic due to formation of high energy surface groups in reactions between the native surface groups of the polymer and the reactive plasma species. 19,20 In addition to surface chemistry, plasma treatment also often affects the surface topography, [20][21][22][23] which further enhances the effect of the surface chemistry on the contact angle. However, the hydrophilization is typically not stable, and either a partial or complete hydrophobic recovery is usually observed.…”

Controlling roughness: from etching to nanotexturing and plasma-directed organization on organic and inorganic materials

“…Starting from a flat surface, within minutes one can get a rough surface, and finally a porous rough layer. X ray photoelectron Spectroscopy (XPS) analysis shown in figure 2b, reveals relatively large surface concentration of Aluminum present in Oxide form (35) coming from sputtering of the Alumina dielectric dome, and the anodized Aluminum clamping ring of the etch tool. This "hard" etch inhibitor creates micromasking and leads to the development of nanotexture.…”

Atmospheric Pressure Plasma Surface Treatment of Rayon Flock Synthetic Leather with Tetramethylsilane

“…Among the different methods, plasma treatment of a polymer surface is an effective technique because of its unique ability to form a thin hydrophobic film on surfaces [5]; this technique can be integrated into continuous production processes [6] also, which means a single-step method for surface modification. Plasma treatment of polymer surface is a well-established technique [7][8][9].…”