Optical properties polytetrafluoroethylene

For the analysis of optical properties, films of all nanostructured systems were prepared by spin-coating from 5 wt% solutions in dichloroethane in a similar way as described above. However, for the morphological study, the solutions were drop cast into polytetrafluoroethylene moulds of 4 cm X 4 cm X 1 cm and the solvent was removed by evaporation at room temperature. All samples were then cured at 140 °C during 24 h and post-cured at 165 °C for 2 h. 

The general structure of this class of materials can, therefore, be summarized as a fine dispersion of metal oxide in a polymer matrix very similar to plasma polytetrafluoroethylene and in principle any metal should be able to be incorporated. Clearly, if the films are protected from the atmosphere, for metals which form involatile fluorides having a relatively weak metal-fluorine bond strength, it should be possible to produce films having metal atoms dispersed in the matrix. It is expected that these films will have many interesting chemical, optical, electrical and magnetic properties., ... 

Since the discovery of Teflon by Roy Plunkett in 1937 a number of fluorinated plastics have reached commercial status. These plastics, exemplified by polytetrafluoroethylene (PIPE), have outstanding electrical, chemical, and thermal properties. AU these commercial materials are either crystaUine or semicrystalline. Teflon AF is a family of amorphous copolymers that retain the desirable electrical, chemical, and thermal properties of semicrystalline fluorinated plastics and also have such properties associated with amorphous materials as optical clarity, improved physical properties, and solubility in selected fluorinated solvents. 

In addition to the standard model systems described above, more exotic particles have been prepared with certain unusual properties, of which we will mention a few. For instance, using seeded growth techniques, particles have been developed with a silica shell which sttrrotmds a core of a different composition, such as particles with magnetic [12], fluorescent [13] or gold cores [14]. Another example is that of spheres of polytetrafluoroethylene (PTFE), which are optically anisotropic because the core is crystalline [15]. 

Hyflon AD amorphous fluoropolymer is used in optical devices, pellicles in semiconductor manufacture, as a dielectric and as a separation membrane. Small amounts of TDD have been used as a modifier in ethylene-chlorotrifluoroethylene polymers to increase stress crack resistance. Minute amounts of TDD are used also as a modifier in polytetrafluoroethylene to improve elastic modulus, reduce creep and permeability and increase transparency. It has been suggested that the much higher reactivity of TDD and other fluorinated dioxoles relative to other modifiers gives a more uniform distribution of the modifier in the polymer chain that results in a greater increase in the desired properties at lower concentration of modifier in the polymer. 

Grum, F., and Saltzman, M. (1976). A New White Standard of Reflectance. Proceedings of the 18th Session C.I.E., C.I.E. Publication No. 18, p. 91. First description of the use of packed PTFE powder as a tranter and working standard for VV-VIS-NIR diffuse reflectance. Weider, V. R., and Hsia, J. J. (1981). Reflection properties of pressed polytetrafluoroethylene powder. J. Opt. Soc. Am. 71, 856 and Weider, V. R., Hsia, J. J., and Adams, B. (1985). Laboratory intercompaiison study of pressed poly-tetrafluoroethylene powder reflectance standards. Appl. Optics 24, 2225. Along with Grum and Saltzman, the definitive works on PTFE as diffuse reflectance standard. 

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