Fluorocarbon, surface energy

Aliphatic dissolution inhibitors, low molecular weight, 15 177 Aliphatic endoperoxides, 18 442, 443 Aliphatic fluorocarbon production Europe, 11 870-871 Pacific Rim/India, 11 871 United States, 11 869-870 Aliphatic fluorocarbons, surface energy of, 21 604... 

There are several compilations and reviews of fluorocarbon physical properties [4, 5, 6 9, 10, II 12], and only the boihng points, surface energies and activities, and solvent properties are discussed in this section to illustrate the characteristic fluonne substituent effects... 

The frictional properties of PTFE are unique Its unusually low static coefficient of fnction decreases with mcreasing load and is lower than the dynamic coefficient of fnction. This precludes stick-shp behavior. The low surface energy also prevents wetting by liquids other than low-surface-tension fluids Like fluorocarbons. 

One type of R substituent that features only briefly in these reviews but which is growing in importance is the fluoroalkyl-containing group. There is renewed interest in fluorosilicone materials of all types including silanes. In line with the well-recognized low surface tension of aliphatic fluorocarbon-containing species, the prime interest is in the area of surface energy control. Examples of such silanes of all three types (n = 1, 2 and 3) have been reported and the purpose of this review is to summarize recent (last decade) developments in this topic. 

This chapter identifies and discusses various epoxy adhesives and the processes that have been used to successfully bond or seal specific substrates. There are only a few materials that epoxy adhesives will not bond well. These uncooperative substrates are most notably low-surface-energy plastics, such as the polyolefins, fluorocarbons, and silicones. However, even these materials can be bonded effectively with epoxy adhesives if a prebond surface treating process is used to change the nature of the substrate surface. Of the other substrate materials, there are some that epoxy adhesives will bond more effectively than others. Table 16.1 lists substrates that generally provide excellent epoxy adhesive joints. 

Because of their high thermal stability and excellent resistance to solvent, fluorocarbons cannot be joined by solvent cementing, and they are very difficult to join by thermal welding methods. Because of their inertness and low surface energy, they also tend to be difficult materials to join by adhesive bonding. Surface treatment is necessary for any practical bond strength to the fluorocarbon parts. 

Recent experimental data [28] indeed show that a weak interface can be created by lowering the surface energy with an fluorocarbon elastomer coating. On such a weakly adsorbing die wall, a macroscopic slip occurs in linear polyeth-ylenes during capillary die extrusion. However, the same surface fails to produce any observable wall slip at low stresses that can be reliably generated in a parallel-plate flow cell. This contrast emphasizes that massive polymer desorption and interfacial slip occur only beyond a critical wall stress. 

Mesophase pitch, derived from coal tar, reacts smoothly with fluorine to give pitch fluoride [147, 148] with a composition between CFi 3 and CFi 6, as a yellowish white solid which differs from graphite fluoride in that it is soluble in some fluorocarbon solvents. Consequently, thin films of pitch fluoride may be deposited on materials and the resulting surfaces have been claimed to have even lower surface energies than PTFE. 

When an insoluble substance of lower surface energy is placed on the surface of another substance of higher surface energy, it will spread until it covers the whole surface provided that the solid-solid interfacial energy is sufficiently low. We can coat a metal pan or a cotton fabric with fluorocarbons to make them non-sticky. 

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