Molecular network system

The network that is formed is highly grafted. A schematic of the final structure is shown in Figure 12, which should be recognized as just one speculation of many. We do not know the precise molecular structure of the molecular network system, beyond the fact that the rubber in it is always uniformly... 

The castings of the molecular network system are transparent to translucent. As the rubber content increased, a brownish hue became apparent. This change often indicates the presence of a degraded amine. The transparency is... 

Figure 13. Proposed morphology of the molecular network system after curing. The domains are shown clearly separated merely for purposes of illustration. In the actual matrix the domains may not be so clearly demarcated.

Figure 18.17 shows that the characteristics of the stress-strain curve depend mainly on the value of n the smaller the n value, the more rapid the upturn. Anyway, this non-Gaussian treatment indicates that if the rubber has the idealized molecular network strucmre in the system, the stress-strain relation will show the inverse S shape. However, the real mbber vulcanizate (SBR) that does not crystallize under extension at room temperature and other mbbers (NR, IR, and BR at high temperature) do not show the stress upturn at all, and as a result, their tensile strength and strain at break are all 2-3 MPa and 400%-500%. It means that the stress-strain relation of the real (noncrystallizing) rubber vulcanizate obeys the Gaussian rather than the non-Gaussian theory. 

SS-LINKED POLYMERS ARE USED in a wide variety of aerospace, automotive, building construction, and consumer product applications. Not all paints, adhesives, composites, and elastomers are cross-linked, but cross-linking systems are often used in these applications when resistance to solvents, resistance to high temperatures, and high mechanical performance are required. These important properties can be traced directly to the three-dimensional interconnected molecular network that is characteristic of cross-linked systems. 

Systems such as the concentrated solution of the UHMWPE in paraffin oil (2-8% w/w) contain a three-dimensional molecular network in which the junction points are produced by secondary valence bonds which cause crystalline regions and by physical entanglements of different life times. Entanglements that are trapped between crystallites have, like the crystallites, essentially infinite life times. 

Rheo-optical and rheological strudies of concentrated solutions of UHMWPE/paraffin oil (2-5% w/w concentration) systems indicate that these are pseudo-gels unlike the covalent bonded molecular networks which exhibit a true gel behavior. The viscoelastic properties of the UHMWPE/paraffin oil pseudo-gels,... 

The other main attribute of aluminosilicate glass is it s ability to contain helium. Most glass containers cannot contain helium for extended periods of time, because the small atoms leak past the glass molecular network. Aluminosilicate glass is considered helium leakproof and is used to contain helium for long periods in a laboratory glass system. 

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