Teflon amorphous fluoropolymer

Very saline samples and/or the addition of organic solvents to the samples were used in early applications in order to provide high refractive indices [88], but the applicability of the LCW flow cell was limited because, in general, only dilute aqueous samples with low refractive indices have been analysed. The development of different kinds of amorphous fluoropolymers (Teflon AFs) with refractive indices lower than that of pure water enabled the design and overall acceptance of flow cells relying on LCWs [89,90]. 

All three commercial amorphous fluoropolymers. Teflon AF, Hyflon AD, and Cytop posses a unique set of properties. All dissolve in fluorinated solvents and thus may be spin coated to produce thin hlms and coatings. The polymers may also be extruded and molded using traditional polymer processing techniques. Note that the polymers are not soluble in hydrocarbon solvents or water and retain the chemical and thermal stability of perfluorinated polymers such as Teflon . These polymers have lower density than the well-known semicrystalline perfluorinated polymers such as pTFE that results in lower refractive index, lower thermal conductivity, higher gas permeability, and lower dielectric constant. The polymers are transparent and have excellent mechanical properties below their Tg due to their amorphous character. The presence of a heterocyclic ring in the polymer backbone of these materials is key... 

Fig. 3.8 Flow inside evaporating droplets with different NaCl concentrations (a) 0.01 wt% (evaporation time (ET) 39 min) (b) 0.1 wt% (ET 45.7 min) (c) 1 wt% (ET 50.5 min) and (d) 10 wt% (ET 63 min). Exposure time was 20 s fin (a), (b), and (c) and 2 s for (d). The substrate was placed on a glass substrate coated with the amorphous fluoropolymer Teflon [76]. Adapted with permission from ref. [76], Copyright 2013 American Institute of Physics...

Table 13.3 Typical properties of Teflon AF amorphous fluoropolymers...

Teflon AF A Family of Amorphous Fluoropolymers with Extraordinary Properties... 

Teflon AF is truly a family of amorphous fluoropolymers with an extraordinary combination of properties. All of the excellent properties of die existing fluoropolymers have either been retained or improved upon and properties arising from the amorphous nature and the presence of microvoids in the AF family of polymers have been added. The similarities and differences of AF and other Teflon polymers are summarized in Table 2.3. This unique combination of properties of Teflon AF amorphous fluoropolymers makes them well suited for applications that had previously precluded polymeric materials,... 

FEP and PFA despite being melt-processible are crystalline (between 50 and 70%). The crystallinity results in poor optical properties (low clarity) and a very poor solubility in organic solvents. The latter makes the preparation of thin optical coatings exceedingly difficult.10 TEFLON AF, an amorphous fluoropolymer, contains in its molecule a bulky dioxole ring, which hinders crystallization. As a result, the polymer has an exceptionally high clarity and excellent optical properties. Its refractive index is the lowest of any plastic.11... 

Resnick, P. R. and Buck, W. H., Teflon AF Amorphous Fluoropolymers, in Modem Fluoropolymers (Scheirs, J., Ed.) John Wiley Sons, New York, Chapter 22 (1997). 

Teflon AF Teflon amorphous fluoropolymer - Dupont trademark... 

Perfluorinated dioxole monomers have been used to prepare a series of amorphous fluoropolymers such as Teflon AF and Hyflon AD. A third amorphous fluoropo-lymer, Cytop contains perfluorotetrahydrofuran and perfluorotetrahydropyran rings, but is prepared in a cyclopolymerization process from an acyclic monomer. These amorphous fluoropolymers retain the outstanding chemical, thermal, and surface properties associated with perfluorinated polymers while also having unique electrical, optical, and solubility characteristics. 

A perfluorinated polymer made by DuPont called Teflon AF breaks down the crystallinity completely, hence its designation amorphous fluoropolymer (AF). It is a copolymer made from 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole (PDD) and TFE. The structure of Teflon AF is shown in Figure 9.170. 

DuPont Teflon AF amorphous fluoropolymers, product information. DuPont, H44587-4 2010. 

Copolymers of tetrafluoroethylene and 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole (PDD) are perfluorinated amorphous polymers and possess unusual combination of properties. They retain the outstanding chemical, thermal, and surface properties of perfluorinated polymers in addition to having excellent electrical and optical properties and have solubility at ambient temperature in a normal fluorosolvent. This family of copolymers is manufactured by DuPont and sold under the trade name of Teflon AF, amorphous fluoropolymers. 

A number of fluoropolymers have been extensively investigated since Roy Plunkett discovered Teflon in 1937. Polytetrafluoroethylene (PTFE) exhibits remarkable electric, chemical, thermal, and mechaiucal properties. Most PTFE-based fluoropolymers arc either crystalline or semicrystalline. However, the Teflon AF series is a family of amorphous polymers that was reported in the literature (Resnick, 1976) because these polymers also showed the desirable electric, chemical, thermal, and mecharucal properties similar to semicrystaUine fluoropolymers. These amorphous fluoropolymers have uruque physical properties such as high... 

Several recent studies report gas permeation, sorption, and free volume characteristics of these two amorphous fluoropolymers. Nemser and Roman (1991 Nemser, 1993) reported permeability properties of Teflon AF polymer membranes prepared by a melt-press method. Similar to PTMSP, these polymers are permeable to permanent gases. For example, oxygen... 

Two major families of amorphous fluoropolymers have been developed. Both rely on in-ehain rings to reduce aystaUinity in flie hcmopo er and in copotymers wifli a-olefins such as tetrafluoroefliylene and chlorotrifluoroethyl-ene. One incorporates 2,2-bis-trifluoromethyl-4,5-difluoro-1,3-dioxole (PDD) in copolymers with tetrafluoroethylene or chlorotrifluoroefc.ylene (TEFLON AF) and flie other is based oi monomas such as 5-oxaperfluoro-l,6-heptadiene, which when polymerized, produce the structure below (CYTOP ). Amorphous fluoropolymers are soluble in a... 

Teflon AF Amorphous Fluoropolymer Product Information product brochure 2041038, Dupont Company, 10/92. 

Amorphous polymers characteristically possess excellent optical properties. Unlike all the other commercially available fluoropolymers, which are semicrystalline, Teflon AF is quite clear and has optical transmission greater than 90% throughout most of the UV, visible, and near-IR spectrum. A spectrum of a 2.77-mm-thick slab of AF-1600 is shown in Figure 2.5. Note the absence of any absorption peak. Thin films of Teflon AF have UV transmission greater Ilian 95% at 200 mm and are unaffected by radiation from UV lasers. The refractive indexes of Teflon AF copolymers are shown in Figure 2.6 and decrease with increasing FDD content. These are the lowest refractive indexes of any polymer family. It should be noted that the abscissa could also be labeled as glass transition temperature, Tg, since Tg is a function of the FDD content of the AF copolymer. Abbe numbers are low 92 and 113 for AF-1600 and AF-2400. 

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