ISSN:
0449-2951
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The dielectric constant of a crosslinked sheet of Viton was measured at two frequencies, 200 cycles/sec. and 100 kcycles/sec., for various elongations. The difference (∊s - ∊∞) decreased sharply when the sample was strained and then increased slowly during stress relaxation. Relaxation was slow at the temperature of these measurements (35°C.), so that we were only able to estimate the behavior at long time for the lowest elongations. Even under these conditions it was possible to demonstrate that the (∊s - ∊∞) values corresponding to long times decrease with elongation. The root mean square dipole moments for a C5F8H2 group are estimated from these data by both a modified form of the Onsager relation and the more recent treatment of Harris and Alder. Stress relaxation and birefringence measurements were performed with elongation and temperature as variables. Viton exhibits linear viscoelastic behavior up to an elongation a of 1.5. The isothermal data indicate a linear relationship between birefringence and stress, both during stress relaxation and recovery. The streas-optical coefficient, C, is 2.35 × 10-4 cm.2/kg. at 28°C. Master curves could be constructed from both the reduced stress and birefringence data a t different temperatures for the same shift factors, aT. The apparent activation energy i s 56 kcal./mole and the characteristic temperature in the simplified WLF equation is TS, = 336 ± 5°C. The birefringence as measured under essentially equilibrium conditions at α = 1.23 was independent of temperature in the range 30-70°C.; however, the CT product measured during relaxation increased from 7 × 10-2 to 8.8 × 10-2 in the same temperature interval. The data were insufficient to determine whether this departure from Gaussian behavior arose from the time dependence or represented an equilibrium effect.
Additional Material:
11 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1963.100010101
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