Perfluorinated coatings

Because It Is resistant to chemical attack, even by strong oxidants at elevated temperature, perfluorinated coatings on electrodes offer a stable environment for attaching reactants. 

Fluoropolymers of different types are commercially available as coating resins [96]. Methods to fabricate perfluorinated coatings and films to impart the desirable properties of perfluorocarbons where they are most needed, without the disadvantages of handling and applying bulk perfluorinated materials are described in the literature [97]. 

Limited solubility in selected perfluorinated solvents (unique amongst commercial fluoropolymers), enabling solution-cast ultra-thin coatings in the submicrometre thickness range. 

Perfluorinated chemicals such as PFOS and perfluorooctanoic acid (PFOA) are usually restricted by brands and eco-labels. Furthermore, the EU regulates the content of PFOS in consumer products on the market. The use of PFOS and PFOA is also restricted by the Stockholm Convention on POPs although some exemptions exist. PFOS are still produced and used in several countries and can be used in the coating of leather. 

Poly(phenylene sulfide-phenyleneamine-phenyleneamine) (PPSAA), 23 709 Poly(phenylene sulfide) (PPS), 10 201-202 23 639, 702, 704 highly sulfonated, 23 719-720 high molecular weight, 23 714 linear perfluorinated, 23 706 powder coatings, 7 41 Poly(phenylene sulfide) composites, 26 764... 

In an attempt to combine band-Uke charge carrier motion realized in an -inevitably fragile - crystalline FET structure with structural robustness and flexibility, Sakanoue and Sirringhaus [167] prepared FETs using spin coated films of 6,13-bis(triisopropylsilylethynyl)(TIPS)-pentacene films in contact with a perfluorinated, low dielectric-constant polymer gate electrode. The (linear) hole mobility at room temperature is 0.8 cm /V s with tendency of an apparent band-like negative temperature coefficient of the mobility (d/i/dT < 0). 

Nafion (17) is a perfluorinated polymer related to teflon (polytetrafluoroethylene). An electrode is conveniently coated by allowing an ethanolic solution of the polymer to evaporate. The film produced is stable, rather more so in fact than other polymer films, e.g. polyvinylpyridine (see Section 57.3.2.2). At the microscopic level the polymer separates into two phases, the bulk polymer and the lower density ionic cluster phase. Diffusion of ions can occur quite freely for example, the diffusion coefficient of Na+ in Nafion (MW 1200) is only slightly less than in water.44... 

Although PDMS is swollen by many organic solvents, it is unaffected by water, polar solvents (e.g., ethylene glycol), and perfluorinated compounds [367]. A detailed study of solvent compatibility of PDMS has been reported. It was found that non-swelling solvents include water, nitromethane, DMSO, ethylene glycol, acetonitrile, perfluorotributylamine, perfluorodecalin, and propylene carbonate [251]. The compatibility of PDMS to other organic solvents can be improved by coating the PDMS surface by sodium silicate [261]. 

Teflon (polytetrafluoroethylene) is a chemically inert polymer used to create nonstick frying pans. Polytetrafluoroethylene can be modified to form a coating, Gore-Tex, which allows the passage of water vapor, but not liquid water, and is used in many articles of clothing. Polymeric perfluorinated ethers are widely used as high performance oils and lubricants. 

Substrates may be dip-coated in solutions or melts of the solid of interest. The technique has been applied, for example, to perfluorinated acids on platinum foil [175], to fluorosurfactants on glass, mica, or silicon wafer [69-72.166.172], and to the production of elastomeric films of butyl rubber [176], The properties of the resulting film are dependent on the concentration of the solution, which is usually low, and on the speed at which the substrate is withdrawn from the liquid. The latter is best controlled by attaching the substrate to an electric motor with a withdrawal speed of between 0.2 and 10 mm/s. 

Curran and co-workers have introduced a promising approach to separation and purification procedures by using fluorocarbon-coated solid phases for liquid-phase chromatography. This approach depends on attaching a variety of perfluorocarbon tags to functional compounds which render the eventual substrate mixture separable over the perfluorinated stationary phase [27, 28] (Figure 7.8). 

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