Rubberlike Elasticity Elastomers

An idea of the present eomplexity of the statistical theory of rubberlike elastieity ean be garnered from Chapter 7 of a recent book on The Physics of Polymers, by Strobl (1996). 

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Elastomers. Elastomers is a generic name for polymers that exhibit rubberlike elasticity. Elastomers are soft yet sufficiently elastic that they can be stretched several hundred percent under tension. When the stretching force is removed, they retract rapidly and recover their original dimensions. 

J.E. Mark, Illustrative modeling studies on elastomers and rubberlike elasticity. In M. Laudon, and B. Romanowiczs (Eds.), International Conference on Computational Nanoscience. Computational Publications, Boston, Hilton Head Island, SC, 2001, p. 53. 

The example chosen here to illustrate this type of composite involves a polymeric phase that exhibits rubberlike elasticity. This application is of considerable practical importance since elastomers, particularly those which cannot undergo strain-induced crystallization, are generally compounded with a reinforcing filler. The two most important examples are the addition of carbon black to natural rubber and to some synthetic elastomers and silica to polysiloxane elastomers. The advantages obtained include improved abrasion resistance, tear strength, and tensile strength. Disadvantages include increases in hysteresis (and thus heat buUd-up) and compression set (permanent deformation). 

The most important property of elastomers and elastoplasts is their accentuated high, hard or soft rubberlike elasticity. The commercially interesting property values in these cases are generally only reached after formulating or compounding with fillers, plasticizers, etc. The subsequent cross-linking depends on the type of rubber, that is, on the nature of the cross-linkable or vulcanizable groups. 

The goals of the new edition of this book are much the same as those described in the Preface to the First Edition, namely a broad overview of elastomers and rubberlike elasticity. Again, the emphasis is on a unified treatment, ranging from chemical aspects such as elastomer synthesis and curing, through theoretical developments and characterization of equilibrium and dynamic properties, to final applications (including tire manufacture and engineering). 

Mark, J. E., Some Unusual Elastomers and Experiments on Rubberlike Elasticity. Prog. Polym. Sci. 2003,28,1205-1221. 

Solution cross-linked elastomers also exhibit stress-strain isotherms in elongation that are closer in form to those expected from the simplest molecular theories of rubberlike elasticity. Specifically, there are large decreases in the Mooney-Rivlin 2C correction constant described in... 

Because of their known structures, such model elastomers are now the preferred materials for the quantitative characterization of rubberlike elasticity. The properties of PDMS networks have been of interest to a variety of groups. " Such specific cross-linking reactions are also useful in the preparation of some of the liquid-crystalline elastomers,discussed in chapter 3. 

Mark, J. E., New Developments and Directions in the Area of Elastomers and Rubberlike Elasticity. Macromol. Symp., Kyoto issue 2003,201, 77-83. 

Mark, J. E. In Illustrative Modeling Studies on Elastomers and Rubberlike Elasticity, 2001 International Conference on Computational Nanoscience, Laudon, M. Romanowicz, B., Eds. Computational Pubheations, Boston Hilton Head Island, SC, 2001 pp 53-56. 

Mark JE. New developments and directions in the area of elastomers and rubberlike elasticity. Macromol Symp Kyoto Issue 2003 201 77-83. 

Mark JE. Some unusual elastomers and experiments on rubberlike elasticity. Prog Polym Sci 2003 28 1205-21. 

In spite of its great fundamental interest and commercial importance, one of the most important unsolved problems in the aiea of elastomers and rubberlike elasticity is the lack of a good molecular understanding of the reinforcement provided by fillers such as carbon black and silica [1-5]. More specifically, the reinforcement of elastomers is an interesting aspect in the basic research of nanocomposites in general, and is of much practical importance since the improvements in properties fillers provide are critically important with regard to the utilization of elastomers in almost all commercially significant applications. Some of the work on this problem has involved analytical theory [6-12], but most of it is based on a variety of computer simulations [13-46]. 

The cases where the filler causes compression of the chain are relevant to another area of rubberlike elasticity, specifically the preparation of networks by cross linking in solution followed by removal of the solvent [57]. This is shown schematically in Figure 14.13. Such experiments were initially carried out to obtain elastomers that had fewer entanglements and the success of this approach was supported by the observation that such networks came to elastic equilibrium much more rapidly. They also exhibited stress-strain isotherms in elongation that were closer in form to those expected from the simplest molecular-theories of rubberlike elasticity. 

The phenomenological theory of rubberlike elasticity is based on continuum mechanics. It provides a mathematical structure from which, in principle, the deformation produced within a vulcanized elastomer by applied surface and bulk forces can be calculated. In the theory, the material is idealized by the assumption that it is perfectly elastic, isotropic in the undeformed state and incompressible. The most general form of the strain energy function (which vanishes at... 

Finally, the possible utilization of model systems in other areas of rubberlike elasticity is illustrated by some brief comments on three important problems of current interest. These are the effects of network chain length distribution on strain-induced crystallization, the properties of networks containing known amounts of well-characterized unattached ( reptating ) chains, and the properties of elastomers consisting of two networks which interpenetrate one another. 

Elastomer. A term used to distinguish a polymer which is elastic or rubberlike from one which is plastic or rigid. 

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