Polytetrafluoroethylene surface properties

Surface Protection. The surface properties of fluorosihcones have been studied over a number of years. The CF group has the lowest known intermolecular force of polymer substituents. A study (6) of liquid and solid forms of fluorosihcones has included a comparison to fluorocarbon polymers. The low surface tensions for poly(3,3,3-trifluoropropyl)methylsiloxane and poly(3,3,4,4,5,5,6,6,6-nonafluorohexyl)methylsiloxane both resemble some of the lowest tensions for fluorocarbon polymers, eg, polytetrafluoroethylene. 

Early in the history of polytetrafluoroethylene, W. A. Zisman recognized its unusual surface properties, and the polymer now finds many uses because its low coefficient of friction eliminates the need for lubrication (Fitzsimmons and Zisman). Shooter and Thomas called attention to the remarkable resistance of polytetrafluoroethylene to seizure, and Bowden (1950) described use of composite structures. These and other investigations have been reviewed and summarized by Allan (1958) (also Allan and Chapman), who showed that the dependence of the coefficient of kinetic friction, fk, on the load in grams, W, is given by the following equation ... 

Surface treatments involving alkali metals are sometimes used to eliminate the characteristic surface properties and promote the adhesion between polytetrafluoroethylene and other substances (Doban Nelson, Kilduff, and Benderly Purvis and Beck Rappaport). It has been shown that these treatments produce a marked increase in the polarity of the surface as measured by the contact angle with various liquids (Allan, 1957). They also increase the coefficient of friction. One interesting application of surface properties of polytetrafluoroethylene was reported by Bowden (1953, 1955) who applied the polymer to the bottoms of his skiis and thereby reduced the friction between the skiis and the snow. 

Where impurities are present as microparticulate material filtration affords a convenient technique for solvent purification. The mobile phase containing added buffers or reagents may be filtered through a 0.5 pm or smaller filter to remove particulate matter that can damage the analytical system. The equipment for filtration is simple. Usually, it consists of an Elenmayer flask connected to vacuum and a reservoir in which a porous filter disk or membrane is placed. The porous disk is usually made from nonporous spherical glass beads (1-2 pm) and/or polytetrafluoroethylene (PTEE). Membrane materials are usually made from PTEE, cellulose, or nylon. To improve the efficiency of the separation process, the surface of the filter disks or membrane surface are often modified chemically, similar to that used for chemically bonded packing materials in RP-HPLC and/or SPE. In this case, the surface properties (hydrophobic or hydrophilic) of filters and/or membranes determine the extent of purification possible. 

Our studies showed that the inner surface of the cardiovascular System was hydrophobic surface with Yc(Zis.)=29 dyne/cm. We could easily select polytetrafluoroethylene as the material with a smaller critical surface tension than 29 dyne/cm to make test materials. Figure-3 shows the surface properties of the inner surface of the cardiovascular system and polytetrafluoroethylene in relation to wetting properties viewed from Zisman s plots. How should we treat polytetrafluoroethylene to minimize the difference in wetting properties between the surface of polytetrafluoroethylene and the inner surface of the cardiovascular system. We tried to improve the surface properties of polytetrafluoroethylene by using the graft copolymerization method and expansion method. 

Matsumoto, H., Kimura, T., Fuse, K., Yamamoto, M., Saigusa, M., Takamatsu, T., and Fiokada, E. Studies on expanded polytetrafluoroethylene as the vascular prosthesis ( the third report) its antithrombogenicity, surface properties and porosity. Artificial Organs. 3 3379197. ... 

Lubricants are added to most polymers at low levels to increase the overall rate of processing or to improve surface properties [1-4], They have been used in the past to facilitate extrusion, injection, compression, etc., of many polymers, mainly PVC, acrylonitrile-butadiene-styrene terpolymer (ABS), PS, PMMA, cellulose acetate (CA), polytetrafluoroethylene (PTFE), and so on. Figure 2.1 shows the relative importance of these polymers as far as the use of lubricants is concerned [5]. The most used lubricants and their relative importance in the United States in 1978 were [6] ... 

Particles of various shapes (particulates and fibers) are produced to be used as additives for many polymers. " Incorporation of polytetrafluoroethylene has little influence on the mechanical properties of the host polymer, but substantial impact on its surface properties and coefficient of friction. Polytetrafluoroethylene is also used as mold coating. Polytetrafluoroethylene-coated molds have excellent release properties, and permit production without external or internal release agents. 

This first systematic XPS analysis has shown that it is possible to sputter-deposit compounds whose surface properties (fluorine to carbon ratio, cross-linking and branching) can be varied over a large range of values, as it has already been observed for polymer films prepared by plasma polymerization. We note here that a film very similar to polytetrafluoroethylene... 

Some authors have suggested the use of fluorene polymers for this kind of chromatography. Fluorinated polymers have attracted attention due to their unique adsorption properties. Polytetrafluoroethylene (PTFE) is antiadhesive, thus adsorption of hydrophobic as well as hydrophilic molecules is low. Such adsorbents possess extremely low adsorption activity and nonspecific sorption towards many compounds [109 111]. Fluorene polymers as sorbents were first suggested by Hjerten [112] in 1978 and were tested by desalting and concentration of tRN A [113]. Recently Williams et al. [114] presented a new fluorocarbon sorbent (Poly F Column, Du Pont, USA) for reversed-phase HPLC of peptides and proteins. The sorbent has 20 pm in diameter particles (pore size 30 nm, specific surface area 5 m2/g) and withstands pressure of eluent up to 135 bar. There is no limitation of pH range, however, low specific area and capacity (1.1 mg tRNA/g) and relatively low limits of working pressure do not allow the use of this sorbent for preparative chromatography. 

Another field of application of fluorinated biomaterials is connected to lesions or evolving disease pathology of blood vessels. In particular, arteries may become unable to insure an adequate transport of the blood to organs and tissues. Polytetrafluoroethylene (PTFE) and expanded e-PTFE are the preferred materials for vascular prostheses. The interactions of blood cells and blood plasma macromolecules with both natural and artificial vessel walls are discussed in terms of the mechanical properties of the vascular conduit, the morphology, and the physical and chemical characteristics of the blood contacting surface. 

In starting a residue analysis in foods, the choice of proper vials for sample preparation is very important. Available vials are made of either glass or polymeric materials such as polyethylene, polypropylene, or polytetrafluoroethylene. The choice of the proper material depends strongly on the physicochemical properties of the analyte. For a number of compounds that have the tendency to irreversible adsorption onto glass surfaces, the polymer-based vials are obviously the best choice. However, the surface of the polymer-based vials may contain phthalates or plasticizers that can dissolve in certain solvents and may interfere with the identification of analytes. When using dichloromethane, for example, phthalates may be the reason for the appearance of a series of unexpected peaks in the mass spectra of the samples. Plasticizers, on the other hand, fluoresce and may interfere with the detection of fluorescence analytes. Thus, for handling of troublesome analytes, use of vials made of polytetrafluoroethylene is recommended. This material does not contain any plasticizers or organic acids, can withstand temperatures up to 500 K, and lacks active sites that could adsorb polar compounds on its surface. 

The volume resistivity of polytetrafluoroethylene remains unchanged even after a prolonged soaking in water, because it does not absorb water. The surface arc-resistance of PTFE resins is high and is not affected by heat aging. They do not track or form a carbonized path when subjected to a surface arc in air [39]. The electrical properties of PTFE are summarized in Table 3.6. 

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