Tetrafluoroethylene plasma-polymerized

Figure lib. Carbon 7s spectrum of tetrafluoroethylene plasma polymerized onto wool. (Reproduced, with permission, from Ref. 42. Copyright 1976, Dekker.)... 

A number of typical polymer-forming monomers have been polymerized using plasma polymerization including tetrafluoroethylene, styrene, acrylic acid, methyl methacrylate, isoprene, and ethylene. Polymerization of many nontypical monomers has also occurred including toluene, benzene, and simple hydrocarbons. 

The effects of the composite parameter WjFM on the friction coefficient of the contact lens coated by methane plasma polymer at a fixed coating thickness 31.2nm are shown in Figure 35.3. The friction coefficient, which is the tangential force divided by the normal force, was calculated from the sliding angle of a contact lens placed on a glass plate that was coated with plasma polymer of tetrafluoroethylene (TFE). The friction coefficient of the methane plasma polymerized contact lens is independent of WjFM in the range 2.6-29.1 GJ/kg. 

There has been a great deal of interest in the study of the electrical properties of plasma polymerized films. Early data on the dielectric and conductivity of the films has been reviewed by Mearns ( ). More recently, the dielectric properties of plasma polymerized styrene (69-71), acrylonitrile (72), hexamethyldisiloxane (73-75), tetrafluoroethylene... 

Plasma Polymerization of Tetrafluoroethylene in a Capacitively Coupled Discharge with Internal Electrodes... 

A capacitively coupled reactor designed to permit continuous coating of a moving substrate with plasma polymer has been described [ 1 ]. In this paper the results of a study of the plasma polymerization of tetrafluoroethylene in such a reactor presented. Plasma polymer has been deposited on aluminum electrodes as well as on an aluminum foil substrate placed midway between electrodes. The study particularly explores conditions in which deposition is minimized on the electrode. For this reason the chemical nature of the polymer formed in a low flow rate (F = 2 cm (S.T.P.)/min) and low pressure (p = 60 mlllltorr) plasma has been analyzed by the use of ESCA (electron spectroscopy for chemical analysis) and deposition rate determinations. This method combined with the unusual characteristics of TFE plasma polymerization (described below) has yielded Information concerning the distribution of power in the inter-electrode gap. The effects of frequency (13.56 MHz, 10 KHz and 60 Hz), power and magnetic field have been elucidated. The properties of the TFE plasma polymer prepared in this apparatus are compared to those of the plasma polymer deposited in an inductively coupled apparatus [2,3]. 

The plasma polymerization of tetrafluoroethylene has also been studied in a straight tube reactor. Deposition rates and ESCA results were obtained as a function of location upstream from, within, and downstream from the induction coll [ ]. It was found that fluorine poor polymer was formed downstream fr m the coil even at the relatively low power level of 1.9 x 10 Joules/kg. Fluorine poor pol3rmer was formed at all locations at 7.7 X 10 Joules/kg. 

The close similarity of the spectra for these three examples (Figure 2) suggests that in all cases, irrespective of the mechanism of removal of material from the cathode or the nature of the cathode material, the polymer matrix formed at the film forming electrode is essentially the same. Furthermore, the overall band profile of the Cis spectra and fluorine/carbon stoichiometries are strikingly similar to those which have previously been reported in the literature for the polymer produced in the plasma polymerization of tetrafluoroethylene ( ). 

Studies of the plasma polymerization of tetrafluoroethylene in such a capacltively coupled system are described in another paper presented at this symposium [ 9]. The apparatus has been used to coat polysulfone hollow fibers with pyridine and acetylene + nitrogen plasma polymer to form a composite reverse osmosis desalination membrane. Salt rejections of 90-93% have been achieved at fluxes of 1.5-2.0 g.f.d with a fiber take up rate of 50-100 cm/min. 

Because of the system dependent aspect of plasma polymerization, there is no material that can be adequately described as the plasma polymer of a particular monomer, e.g., the plasma polymer of styrene, the plasma polymer of tetrafluoroethylene, and so on. The factors that influence the system dependent aspect of plasma polymerization are operational parameters, such as flow rate, discharge power, system pressure, and substrate temperature, and the design factors of the reactor, such as its size and shape, mode of electric discharge, and location of the substrate. 

The strategy proposed by Yameen and coworkers [9] is more generally applicable as demonstrated by the successful grafting on five technologically important substrates poly(propylene) (PP), poly(ether ether ketone) (PEEK), PET, poly(tetrafluoroethylene) (FIFE), and poly(4,4 -oxydiphenylene pyromellitimide) (PI). The approach involved poly(allylamine) deposition on these substrates by pulsed plasma polymerization. The amine functionalities of the resulting adlayer were then used for the attachment of ATRP initiators. 

Fig. 22. Pull-off force histograms recorded with a SiO probe on PS, isotactic PP, PVDF, and poly-(tetrafluoroethylene-co-hexafluoropropylene) (FEP), respectively, in perfluorode-caline (left) and force titration of plasma-polymerized allylamine films as measured in buffer using hydroxyl-terminated SFM tips together with representative f-d curves (right). The f-d curves display (depending on the pH of the buffered aqueous solution) (a) exclusively repulsive (pH 4.7), (b), (c) repulsive and attractive (pH 5.3 and 6.2, respectively), or (d) exclusively adhesive interactions (pH 6.8). Reprinted in part with permission from Ref. 86 (left). Copyright (1998) American Chemical Society, and Ref 216 (right). Copyright (2000) American Chemical Society.

If a polymer is formed throu plasma-induced polymerization from tetrafluoroethylene, the ESCA Cls spectrum should be identical to that of Teflon. Therefore, the fact that the ESCA Cls peaks are significantly different from those in the spectrum of Teflon indicates that a major portion of the glow discharge polymerization is not plasma-induced polymerization. How the balance between plasma state polymerization and plasma-induced polymerization is influenced by the conditions of glow discharge and the location of polymer deposition within a reactor can be seen by comparing the ESCA Cls spectra shown in Figures 2-4. 

Besides plasma techniques, surface photopolymerization (25 31) is another versatile method for modifying a polymer or a metal surface with a thin coating (<50o2). The process involves polymerizable or nonpolymerizable compounds. Under UV radiation, tetrafluoroethylene and many vinyl monomers can be polymerized. Other compounds including imides, anhydrides, saturated hydrocarbons, and ketones can all be used for the in vacuo deposition process. 

Turmanova, S. Minchev, M. Vassilev, K. Danev, G. Surface grafting polymerization of vinyl monomers on poly(tetrafluoroethylene) films by plasma treatment. J. Polym. Res. 2008,15 (4), 309-318. 

Coulson et al. [44] report high repellence towards polar as well as non-polar liquids from micro-rough poly(tetrafluoroethylene) (PTFE) surfaces. In a first step, the samples were roughened by air plasma treatment, after which a thin-layer was polymerized from 1H,1H,2H,2H-heptadecafluorodecyl acrylate vapor in the same apparatus. 

The plasma may induce the polymerization of a constituent of the gas phase and so cause deposition of a thin polymeric film, or primer, onto the substrate. Several workers have explored this route for depositing a primer, to which another polymer is subsequently adhered, or for depositing a protective coating directly onto a metal substrate [216-223]. For example, Nichols et al. [217] have deposited polymeric primer films, about 30 nm thick, from glow-discharge polymerization of methane tetrafluoroethylene or tetramethyl-disiloxane onto platinum wires. These primers were then coated with a few-micron-thick layer of either poly(p-xylylene) or poly(chloro-p-xylylene), which are good electrical insulators in thin-film applications provided this coating... 

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