Teflon molecular structure

Nearly all of the commercially available membranes are based on Nafion. Nafion also has the largest body of literature devoted to its study because of its demonstrated industrial importance and availability. Nafion composite systems also have already become significant in both industrial and academic research. In composite structures, Nafion can be impregnated into an inert Teflon-like matrix (i.e. W. L. Gore membranes ), or inorganic additives can be added to a supporting Nafion matrix for improved physical or electrochemical properties (i.e. lon-omem °). Some critical aspects of Nation s molecular structure and physical properties will be briefly highlighted to provide a baseline for comparison with the other alternative materials discussed in this review. 

FIGURE 23.7 A model of the molecular structure of Teflon shows that the fluorine atoms shield the carbon chain very effectively. Note that the chain must twist to accommodate the bulk of the fluorine atoms, completing a full spiral every 26 C atoms along the chain. 

Polytetrafluoroethylene is a completely fluorinated polymer manufactured by free-radical polymerization of tetrafluoroethylene. With a linear molecular structure of repeating -CF2—CF2- units, PTFE is a crystalline polymer with a melting point of 326.7°C. Its specific gravity is 2.13—2.19. Polytetrafluoroethylene has exceptional resistance to chemicals. Its dielectric constant (2.1) and loss factor are low and stable across a wide range of temperature. It has useful mechanical properties from myogenic temperatures to 260°C. In the United States, PTFE is sold as Halon, Algoflon, Teflon, Fluon, Hostaflon, and Polyflon. ... 

Polytetrafluoroethylene (PTFE), also known by its generic DuPont tradename of Teflon, is a linear polymer that has a molecular structure similar to PE, but with all the hydrogen-atoms replaced by fluorine atoms (CE2-CE2) . Since fluorine-atoms prefer contact with fluorine-atoms, while repelling all others, this repulsion reduces the friction coefficient of the system and produces a non-adhesive surface (with self-lubricating properties). The strong C-C and C-F bonds make PTFE chemically inert, with excellent chemical resistance. 

Physical Properties and Molecular Structure 77 THE CHEMISTRY OF... Fluorocarbons and Teflon 82... 

Tensile specimens of polypropylene, polycarbonate. Mylar (polyester), Nomex (nylon paper), and Kapton (polyimide) had dimensions of 3 mm in width and 10 mm in guage length. The specimen thicknesses were 65 ym for polypropylene, 75 ]lm for polycarbonate, 85 ym for Mylar, 200 ym for Nomex, and 50 ym for Kapton. Their tensile axes were perpendicular to the rolling direction of the sheets. The molecular structures of these specimens are shown in Table I. Epoxy resins were tested by compression. The specimens of epoxy resin were made of Epikote 828 (bisphenol A type) hardened by K61B (tridimethylaminophenol) or polyamide in a teflon mold of 2 mm in diameter and about 6 mm in height. 

Basic research is carried out for the sake of increasing knowledge, such as how and why a specific reaction occurs and what the properties of a substance are. Chance discoveries can be the result of basic research. The properties of Teflon", for example, were first discovered by accident. A researcher named Roy Plunkett was puzzled by the fact that a gas cylinder used for an experiment appeared to be empty even though the measured mass of the cylinder clearly indicated there was something inside. Plunkett cut the cylinder open and found a white solid. Through basic research, Plunkett s research team determined the nonstick properties, molecular structure, and chemical composition of the new material. 

The final mixture was loaded into a 50 mL Teflon-lined stainless steel autoclave and heated at 180 °C for 40 h without agitation. The solid product was filtered off, washed with distilled water, and dried at 105 °C. The product was uniform small crystals with a size of 6 pm. Powder XRD pattern characterization of the solid product showed a fully crystalline MFI structure. Elemental analysis gave an Si/Al ratio of 12-13.5, which is tunable by adjusting the ratio of source materials in the precursor gel. The absence of A1 species in the present synthetic system leads to the formation of the high-quality all-silica ZSM-5-type molecular sieve termed silicalite-I. Moreover, high-quality [B]-ZSM-5, [Fe]-ZSM-5, or [Ti]-ZSM-5-type molecular sieves could be obtained by the addition of B203, Fe2(S04)3, or Ti(OC2H5)4 to the synthetic system of silicalite-I and crystallization at 200, 180, or 175 °C for several days, respectively. 

It seems likely that the free siloxane polymers deposited on teflon surfaces are different in structure from the relatively thin films deposited on the glass surface when using siloxanes as coupling agents. However, it is likely that they have many features in common, including the effect of silane solution concentration on the relative molecular weight of the cured siloxane coating, as evidenced by the DMA studies. 

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