Fluorinated system stability

The disappearance of the sharp Verwey transition was discussed by Mott (1979), who suggested that at low temperatures the material is a Wigner glass , the electrons (Fe2 + ions) being frozen into random sites and the whole system stabilized by the fluorine. Discussion of the thermopower measurements show, according to Mott (1979), that a hopping mechanism is operative at low T. Ihle and Lorenz (1985), however, consider that the electrons in the wrong sites move by a small polaron band mechanism. 

Fluorocarbons and fluorinated amphiphiles have found a variety of applications in materials science and medicine [1-5]. As many of these applications involve colloidal systems stabilized by a monolayer of fluorinated amphiphiles, it is essential to understand the structure and properties of these interfacial films. Such knowledge can provide improved control over the engineering and properties of highly fluorinated colloids and interfaces [6]. 

Shchukin, E. D., Amelina, E. A., and A. M. Parfenova. 2008. Stability of fluorinated systems Structure-mechanical barrier as a factor of strong stabilization. In Highlights in Colloid Science, D. Platikanov and D. Exerova (Eds.), pp. 41-53. New York Wiley-VCH. 

Stability of Fluorinated Systems Structure-Mechanical Barrier as a Factor of Strong Stabilization... 

A -dien-3-ol ethers gives rise to 6-substituted A" -3-ketones. 6-Hydroxy-A" -3-ketones can be obtained also by autooxidation.Structural changes in the steroid molecule may strongly affect the stability of 3-alkyl-A -ethers. Thus 11 j5-hydroxyl and 9a-fluorine substituents greatly increase the lability of the enol ether/ while halogens at C-6 stabilize this system to autooxidation and acid hydrolysis. 

One of the most important parameters that defines the structure and stability of inorganic crystals is their stoichiometry - the quantitative relationship between the anions and the cations [134]. Oxygen and fluorine ions, O2 and F, have very similar ionic radii of 1.36 and 1.33 A, respectively. The steric similarity enables isomorphic substitution of oxygen and fluorine ions in the anionic sub-lattice as well as the combination of complex fluoride, oxyfluoride and some oxide compounds in the same system. On the other hand, tantalum or niobium, which are the central atoms in the fluoride and oxyfluoride complexes, have identical ionic radii equal to 0.66 A. Several other cations of transition metals are also sterically similar or even identical to tantalum and niobium, which allows for certain isomorphic substitutions in the cation sublattice. 

The fluorine content, density, critical surface energy, glass transitions, thermal expansion coefficient above and below the glass transition, and 300°C isothermal thermogravimetric stabilities of the fluoromethylene cyanate ester resin system with n = 3, 4, 6, 8, 10 are summarized Table 2.2. Also included for the purpose of comparison are the corresponding data for the aromatic cyanate ester resin based on the dicyanate of 6F bisphenol A (AroCy F, Ciba Geigy). 

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