The Diffusion‐reaction Model on the Wettability Gradient Created by SF₆ Plasma

Abstract

Previously a model was reported on the simulation of a SF6 plasma generated wettability gradient by considering only the diffusion of the reactive species in plasma. This study proposed a modified model to describe the wettability gradient created by SF6 plasma by further considering the chemical reactions between the plasma species and the substrate. The wettability gradient was prepared by applying SF6 plasma on the O2 plasma pretreated polypropylene film that was covered with a mask. Experimentally, the chemical composition and surface wettability along the gradient was characterized by electron spectroscopy for chemical analysis, contact angle measurements and atomic force microscopy. For the mathematical model, two main assumptions were made for the formation of gradient on the surface of substrate: (i) the dissociation and ionization of SF6 plasma in the vacuum chamber followed the diffusion‐adsorption‐reaction processes and (ii) the fluorine radicals were the principle reactive species. The computation of the numerical solutions was facilitated by the finite element method. The simulated surface fluorine content and surface wettability matched exceptionally (≈95%) with the experimental results. The numerical evaluation of the spatial distribution of plasma reactive species in the mask in y‐ and z‐directions and t‐domain also assisted the understanding of the surface interactions on the gradients.

Impurity Removal of Waste Cooking Oil Using Hydrophobic Polypropylene Hollow Fiber Membrane

“…The water contact angle (WCA) and oil contact angle (OCA) indicate the hydrophobic and oleophilic properties of the membrane, respectively [38][39][40]. Membrane surface wettability was determined by measuring the static contact angles of liquid droplets [41,42]. In this study, the contact angles were determined by dropping 1 μL of deionized water and fresh oil, respectively, onto the membrane surface.…”

Comparison of SF6 and CF4 Plasma Treatment for Surface Hydrophobization of PET Polymer

“…Fluorine-containing plasmas are often used for the surface hydrophobization of polymer materials [1,2,3,4,5,6,7,8] and for dry-etching in the semiconducting industry [9,10,11,12]. In the latter, the addition of oxygen is used to enhance the etching rate [11].…”

“…SF 6 is rarely used, and therefore, literature is scarce. SF 6 plasma has been used to treat polyethylene terephthalate PET (fabric [1], fibres [7] or film [5]), cotton fibres [7], polypropylene (PP) [3,4], polyethylene (PE) [5], polyvinyl chloride (PVC) [5] and polymethyl methacrylate [2]. The authors reported increased hydrophobicity; however, different authors reported different stabilities of the hydrophobic surface.…”

“…Mangindaan et al prepared gradient PP surfaces with wettability between 20° and 135° by applying an O 2 pretreatment followed by SF 6 plasma treatment under a specially designed mask with an open end and a closed end, which allowed the diffusion of reactive fluorine species [3,4]. The highest fluorine content of 44 at % was found at the open end, and only 3 at % was found at the close end of the mask.…”

Formation of lateral chemical gradients in plasma polymer films shielded by an inclined mask

“…When a substrate is covered with a one‐end open mask, a constant diffusion rate of the plasma reactive species is obtained . Mangindaan et al started to determine the mechanism related to the production of lateral gradients onto polypropylene substrates using such a mask in the static configuration. A model consisting of three sub‐processes was proposed: 1) bulk diffusion of the plasma reactive species; 2) interfacial adsorption/desorption; and 3) surface chemical reactions.…”