Selective Etching of Semicrystalline Polymers:  CF₄ Gas Plasma Treatment of Poly(ethylene)

Abstract

A series of poly(ethylene) (PE) films with different degrees of crystallinity was treated with a radio-frequency tetrafluoromethane (CF4) gas plasma (48−49 W, 0.06−0.07 mbar, and continuous vs pulsed treatment). The etching behavior and surface chemical and structural changes of the PE films were studied by weight measurements, X-ray photoelectron spectroscopy (XPS), static and dynamic water contact angle measurements, scanning electron microscopy (SEM), and atomic force microscopy (AFM). With increasing crystallinity (14−59%) of PE, a significant and almost linear decrease of the etching rate was found, ranging from 50 Å/min for linear low-density poly(ethylene) (LLDPE) to 35 Å/min for high-density poly(ethylene) (HDPE). XPS analysis revealed that after CF4 plasma treatment the PE surfaces were highly fluorinated up to F/C ratios of 1.6. Moreover, CF4 plasma treatment of PE resulted in extremely hydrophobic surfaces. Advancing water contact angles up to 150° were measured for treated LDPE films. Both SEM and AFM analysis revealed that pronounced surface restructuring took place during prolonged continuous plasma treatment (≥15 min). The lamellar surface structure of LDPE changed into a nanoporous-like structure with uniform pores and grains on the order of tens of nanometers. This phenomenon was not observed during plasma treatment of HDPE films. Apart from surface roughening due to selective etching, pulsed plasma treatment did not result in significant surface structural changes either. Therefore, the restructuring of continuously plasma-treated surfaces was attributed to a combined effect of etching and an increase of the surface temperature, resulting in phase separation of PE-like and poly(tetrafluoroethylene)-like material, of which the latter is surface oriented.

Tailoring the Properties of Asymmetric Cellulose Acetate Membranes by Gas Plasma Etching

“…At the surface of CF 4 pulse-treated CTA the amount of fluorine was lower than that for continuously treated membranes. Results from a previous paper on CF 4 plasma treatment of low-density poly(ethylene) (LDPE) films confirm that pulsed-treatment causes somewhat less fluorination (26). Also, some silicium was exposed at the surface of the pulse treated CTA membrane, which is similar to the values found for untreated or short CO 2 plasma-treated membranes (<2 min).…”

“…No significant differences of surface structure could be found between pulse-treated (900 × 1 s) and continuously treated (15 min) CTA membranes. This indicates that, the actual plasma time of both treatments being the same (900 s), the total etch effect on the surface structure is also similar, despite the fact that the conditions for pulsed treatment were much milder (26). Figure 3 shows that CF 4 plasma treatment had a completely different effect on the surface structure of the membrane's top layer.…”

“…Perhaps the most plausible reason for the lack of silicium at the treated membrane's surface is found in surface restructuring during CF 4 plasma-treatment. The surface nanopores could fuse together due to a local temperature rise caused by etching and fluorination (exothermic) (26). Thus, the silica particles remain covered by a thin, restructured, and fluorinated polymer layer.…”

“…Carbon dioxide (CO 2 ) and tetrafluoromethane (CF 4 ) are used as discharge gas. The former is an oxidative etchant (2), while the latter is known as a mild, highly fluorinizing etchant (26). After gas plasma etching the top layer structure of the membranes is analyzed by scanning electron microscopy (SEM).…”

Improved adhesion of TiO2‐based multilayer coating on HDPE and characterization of photocatalysis

“…The plasma treatment of the HDPE roughens the surface because of selective etching in which amorphous phase is being etched faster than the crystalline phase. 44 The plasma interacts with HDPE leading to carbon-carbon bond scissions and creates oxygen-containing hydrophilic functional groups (e.g., C¼ ¼O and COOH) on the HDPE surface. 45 Plasma treated (30 s at 200 W) surface of HDPE becomes hydrophilic observed as a decrease in water contact angle from 97 (S1) to 50 (S4) ( Table II).…”