Polymers cryogenic properties

Hartwig G (1986) Cryogenic properties. In Encyclopedia of polymer science and engineering, 2nd edn, vol 4, John Wiley, New York, p 450... 

Future investigations may result in the development of completely new polymers, whose properties may be significantly better at cryogenic temperatures. However, we believe that sealant systems based upon present technology may be used to advantage in the fabrication and repair of cryogenic containers. 

Hartwig, G. Polymer Properties at Room and Cryogenic Temperatures, Plenum Press, New York, 1994, Chapter 4. 

A torsional pendulum (Figure 5.80) is often used to determine dynamic properties. The lower end of the specimen is clamped rigidly and the upper clamp is attached to the inertia arm. By moving the masses of the inertia arm, the rotational momentum of inertia can be adjusted so as to obtain the required frequency of rotational oscillation. The dynamic shear modulus, G, can be measured in this manner. A related device is the dynamic mechanical analyzer (DMA), which is commonly used to evaluate the dynamic mechanical properties of polymers at temperatures down to cryogenic temperatures. 

Subject areas for the Series include solutions of electrolytes, liquid mixtures, chemical equilibria in solution, acid-base equilibria, vapour-liquid equilibria, liquid-liquid equilibria, solid-liquid equilibria, equilibria in analytical chemistry, dissolution of gases in liquids, dissolution and precipitation, solubility in cryogenic solvents, molten salt systems, solubility measurement techniques, solid solutions, reactions within the solid phase, ion transport reactions away from the interface (i.e. in homogeneous, bulk systems), liquid crystalline systems, solutions of macrocyclic compounds (including macrocyclic electrolytes), polymer systems, molecular dynamic simulations, structural chemistry of liquids and solutions, predictive techniques for properties of solutions, complex and multi-component solutions applications, of solution chemistry to materials and metallurgy (oxide solutions, alloys, mattes etc.), medical aspects of solubility, and environmental issues involving solution phenomena and homogeneous component phenomena. 

At present it is very difficult to estimate the synergetic effects of high mechanical loads, cryogenic temperatures and high fluences of nuclear radiation on polymer materials. In this review, therefore, the effects of each above-mentioned factor on the polymer properties will be separately introduced. 

The available data on the mechanical properties of polymer materials at cryogenic temperatures have been reported for the last few decades mainly in close connection with space technology. 

An extensive compilation and evaluation of mechanical, electrical, and thermal properties of six commercially available polymers was performed by Reed et al. [14]. It was shown in their summarized data that polypyromellitim-ide (PPMI), which is obtained by the polycondensation between pyromellitic acid and aromatic diamine, exhibits excellent mechanical properties at both high and low temperatures and retains ductility even at cryogenic temperatures, as seen in Fig. 1. 

The electrical properties of insulators for superconducting magnets are of crucial importance in relation to the operational reliability of fusion reactors [81], In the present section, the characteristics in original electrical properties of polymers at cryogenic temperatures are briefly introduced and then the effects of radiation on these properties are surveyed. 

In addition to high breakdown strength, the electrical insulators for superconducting magnets must have excellent dielectric properties at cryogenic temperatures. Chant reported the results of measurements on dielectric constant and loss tangent (tan 5) for several polymers over the temperature range from 4.2 to 300 K [83], The variation of dielectric constant of samples as a function of temperature is shown in Fig. 15. The dielectric constants of nonpolar polymers, such as polyethylene, polypropylene and polytetrafluoroethylene, are substantially independent of temperature, whereas those of polar polymers except polyimide decrease by a maximum of 20% as the temperature is reduced. The values of tan 8 at the frequency of 75 cps for nonpolar polymers decreased by... 

It is generally considered that the electrical properties of polymers and composites tend to increase their values to advantageous regions on cooling to cryogenic temperatures. 

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