Elastomers comparisons between different

An extension of rubber elasticity (i.e. of the description of large, static and incompressible deformations) to nematic elastomers has been given in a large number of papers [52, 61-66]. Abrupt transitions between different orientations of the director under external mechanical stress have been predicted in a model without spatial nonuniformities in the strain field [52,63]. The effect of electric fields on rubber elasticity of nematics has been incorporated [65]. Finally the approach of rubber elasticity was also applied recently to smectic A [67] and to smectic C [68] elastomers. Comparisons with experiments on smectic elastomers do not appear to exist at this time. Recently a rather detailed review of the model of an-... 

TABLE 16.2 Comparison between Two Mechanical Properties of Different Actuating Materials Skeletal Muscles, Thermomechanical (Thermal Liquid Crystals and Thermal Shape Memory Alloys), Electrochemomechanical (Conducting Polymers and Carbon Nanotubes) and Electromechanical (Ionic Polymer Metal Composites, Field Driven Liquid Crystal Elastomers, Dielectric Elastomers)... 

The wide choice available in plastics makes it necessary to select not only between TPs, TSs, reinforced plastics (RPs), and elastomers, but also between individual materials within each family of plastic types (Chapters 6 and 7). This selection requires having data suitable for making comparisons which, apart from the availability of data, depends on defining and recognizing the relevant plastics behavior characteristics. There can be, for instance, isotropic (homogeneous) plastics and plastics that can have different directional properties that run from the isotropic to anisotropic. Here, as an example, certain... 

The new polymers are intermediate in composition and crystallinity between the essentially amorphous EPR and the semicrystalhne iPP. The presence of the complementary blocks of elastomers for both ethylene and propylene crystallinity should not indicate a similarity, beyond the levels of the crystallinity in the properties of the E-plastomers and the P-plastomers. The E-plastomers and the P-plastomers differ in their stmctural, rheological, as well as their thermal, mechanical, and elastic properties. In a comparison of the tensile strength and tensile recovery (tension set) from a 100% elongation for a range of P-plastomers and E-plastomers, the former have lower tension set than EPR and iPP. However, for comparative E-plastomers and P-plastomers at equivalent tensile strength, the latter have significantly better tension set. In summary, P-plastomers are tough polyolefins which are uniquely soft and elastic. 

Obviously, there are many subtle differences in the structure, morphology, or network topology between radiation cured and sulfur cured elastomers, but their physical properties may be nearly equal, provided that precautions are taken to avoid the occurrence of chain scissions. A comparison of radiation cross-linked and sulfur cured natural rubber (gum and carbon-black-reinforced compounds) is in Table 5.4. ... 

Summarizing, it can be concluded that a relatively sharp (within 2-4% of deformation) drop in H is observed for copolymers of PBT but in comparison with homo-PBT this transition occurs at much higher deformations (between 25 and 30%). This difference as well as the following increase and decrease of H are related to the structural peculiarities of thermoplastic elastomers - the presence of a soft amorphous phase which first deforms and the existence of a physical network. The very low H values obtained for PEE are related to the fact that the PBT crystallites are floating in an amorphous matrix characterized by a low viscosity. 

There are a number of models for polarization of heterogeneous systems, many of which are reviewed by van Beek (23). Brown has derived an exact, though unwieldly, series solution using point probability functions (24). For comparison to spectra for the thermoplastic elastomers of interest here, the most useful model seems to be the one derived by Sillars (25) and, in a slightly different form, by Fricke (26). The model assumes a distribution of geometrically similar ellipsoids with major radii, r-p and rj which are randomly oriented and randomly distributed in a dissimilar matrix phase. Only non-specific interactions between neighboring ellipsoids are included in the model. This model includes no contribution from the polarization of mobile charge carriers trapped on the interfacial surfaces. 

The abrasion resistance of a rubber has been related to the ability of a rubber to undergo rapid deformation. In turn this is a function of segment flexibility which increases with an increase in the difference between the Tg and the test temperature. Since the TgS of the polybutadienes are low the abrasion resistance of polybutadiene vulcanizates is, as may be expected, good in comparison to other elastomers. 

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