Poly dielectric loss behavior

Dielectric Behavior The dielectric loss behavior of poly-sulfone samples was measured below 23 C as a function of unasso-... 

The dielectric loss behavior of PVAc was similar to that of the other polymers. An Increase in dielectric Intensity of the polymer s S mechanism was directly proportional to the amount of unclustered water. In addition when clustered water was present two separate low temperature peaks occurred as shown In the frequency dependent data of Figure 8. The higher frequency peaks were the result of clustered water. This is confirmed by the similarity between poly(vinyl acetate) and the clustered water peaks of other polymers as plotted in Figure 7. 

Water absorbed in a polymer can exist in an unassociated state or as a separate phase (cluster). In this investigation the DSC technique of water cluster analysis was used in conjunction with coulometric water content measurements to characterize the water sorption behavior of polysulfone and poly(vinyl acetate) The polysulfone had to be saturated above its Tg (190°C) and quenched to 23°C for cluster formation to occur while cluster formation occurred isothermally at 23°C in the poly(vinyl acetate) Both polymers showed an enchancement of their low temperature 3-loss transitions in proportion to the amount of unclustered water present. Frozen clustered water produced an additional low-temperature dielectric loss maximum in PVAc and polysulfone common to polyethylene and polycarbonate as well. Dielectric data obtained on a thin film of water between polyethylene sheets was in quantitative agreement with the clustered water data. 

Poly (ethylene terephthalate) (PET) is one of the most common polymers provided by the polymer industry for fiber and packaging purposes [24]. As far as polymer crystallization is concerned, PET can be considered as a paradigm of a crystallisable polymer due to the fact that PET can be obtained either in the amorphous state or with a controlled amount of ciystalUnity. Therefore, PET has been used to study the influence of crystallinity in a great variety of physical properties including thermal behavior [16,25-29], structure development [30-33] and mechanical and dielectric behavior among others [13,14,34,35]. Figure 21.7 presents the dielectric loss, e", and dielectric constant, e, for amorphous PET at T > 7 as a function of frequency for different temperatures. 

Polyethylene samples were also exposed to conditions which created 0.4% clustered water and dielectric data taken at low temperatures on the samples. The same loss maximum noted In polycarbonate and polysulfone near -100 C at 1 kHz was also noted In polyethylene. A special polyethylene sample was molded around a PTFE sheet. The PTFE was removed and replaced with distilled water. This sample was equivalent to a thin water layer between polyethylene sheets. The dielectric behavior of this sample was quantitatively equivalent to that of the polyethylene containing spherical clusters of water if the difference in geometry of the water phase is taken into account. Figure 7 shows the logarithm of the frequency of loss maxima due to water clusters versus reciprocal temperature for polyethylene, polycarbonate, poly(vlnyl acetate and polysulfone. The polysulfone data from Allen are shown for comparison and It Is seen that the data can be Interpreted as a single mechanism with an activation energy of 7 kcal/ mole. 

With the new cell It was possible to measure dielectrically the a transition behavior of poly(vinyl acetate) while retaining water within the sample. Figure 10 shows the normalized loss for the at transition for 0.2, 2.0 and 4.5% unclustered water. 

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