Atmospheric pressure plasma enhanced chemical vapor deposition of hydrophobic coatings using fluorine-based liquid precursors

Abstract

In this work, an atmospheric pressure plasma jet (APPJ) was investigated for developing hydrophobic thin film coatings on ultra-high molecular weight polyethylene (UHMWPE) films. Fluoroalkyl silanes, (CH3CH2O)3SiCH2CH2(CF2)7CF3 and (CH3O)3SiCH2CH2CF3 and fluoroaryl silane, F5ArSi(OCH2CH3)3 monomers with different fluorocarbon chain lengths were polymerized via plasma enhanced chemical vapor deposition (PECVD). These precursors in addition to other deposition processing conditions such as electrode-substrate gap distance and deposition time were investigated to understand the influence these parameters have on the overall deposition characteristics and hydrophobic behavior of the as-deposited thin film coatings. Attenuated total reflectance–Fourier transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) techniques revealed that the chemical composition of the coatings retained a bulk of the monomer chemistry, signifying a low degree of fragmentation of the precursor in the plasma. This was particularly demonstrated by the coatings obtained with the fluoroaryl silane precursor, where the aromatic structure was kept intact. The hydrophobicity of the coatings was assessed using water contact angle (WCA) measurements and the thickness and morphology were examined using profilometry, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Variations in the composition of fluorocarbon coatings were observed as a result of deposition conditions, however the dominant parameter was found to be the monomer precursor. Optimal hydrophobic behavior was observed from coatings derived from the monomer with the longest fluorocarbon chain, as demonstrated from trends seen in WCA and CFn group concentrations.