Fluoropolymers moduli

FIG. 12 Radius, r(t), of dry patches growing in an unstable TCP fihn on silicone mbber (RTV 615, General Electric Co.), of different shear modulus, p,. Teflon PFA is a hard fluoropolymer of similar surface free energy (y = 20 mJ-m ). 

The carbon chain is in a planar zigzag orientation and forms an orthorhombic lattice with interpenetration of adjacent chains.61 As a result of this structure, ETFE has an exceptionally low creep, high tensile strength, and high modulus compared to other thermoplastic fluoropolymers. Interchain forces hold this matrix until the alpha transition occurs at about 110°C (230°F), where the physical properties of ETFE begin to decline and more closely resemble perfluoropolymers properties at the same temperature. Other transitions occur at -120°C (-184°F) (gamma) and about -25°C (-13°F) (beta).62... 

FIGURE 3.4 Flexural modulus values (ASTM D790). (From Scheirs, J., Ed., Modem Fluoropolymers, John Wiley Sons, Ltd., 1997. With permission.)... 

The moduli of fluoropolymers are a function of a number of variables, most important of which is the composition of the polymer and, more specifically, the presence or absence of hydrogen in the polymer. Other variables are those affecting the other mechanical properties of these plastics. They include testing temperature, molecular weight, and crystallinity, which affect the modulus of these plastics independently of the regime/tyqie of measurements. Perfluo-ropolymiers have lower moduli than partially fluori-nated fiuoropiastics. An increase in the fluorine content of the fluoroplastic increases the modulus. 

Linear elasticity is the most basic of all material models. Only two material parameters need to be experimentally determined the Young s modulus and the Poisson s ratio. The Young s modulus can be directly obtained from uniaxial tension or compression experiments, and typical values for a few select fluoropolymers at room temperature are presented in Table 11.2. 

Table 11.2. Representative Values of the Young s Modulus at Room Temperature for a Few Select Fluoropolymers...

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. 

Here, (pi is the volume fraction of droplets with radius i ,. The volume-averaged radius can be used instead of the distribution if the polydispersity is less than 2.3. The fit to G data for a 6.5% dispersion of poly(ethylene terephthalate) in a linear fluoropolymer at 300 °C, with an average droplet radius of 5.4 /rm, is shown in Figure 14.4, where the data are plotted as the ratio of the storage modulus of the blend to that of the matrix polymer. The peak reflects the frequency regime where the interfacial dynamical response is sensitive to interfacial tension. Interfacial tension acts like an elastic stress, so the major contribution of the interface is in G . The interfacial tension of the blend estimated from standard equations is about... 

To avoid the negative properties of PDMS and variations of PDMS, researchers have investigated the use of fluoropolymers as mold materials in soft lithography. Fluoropolymer elastomeric moltb have lowered surface energies, tunable modulus, chemical stability, transparency to visible light, and solvent resistance. Rolland et have developed photocurable... 

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