Rubber-like elasticity thermodynamics

The above-mentioned general features of elastomeric materials have long been known and, in fact, the area of rubber-like elasticity has had one of the longest and most distinguished histories in all of polymer science (1,2,16). Forex-ample, quantitative measurements of the mechanical and thermodynamic properties of natural rubber and other elastomers go back to 1805, and some of the earliest studies have been carried out by such luminaries as Joule and Maxwell. Also, the earliest molecular theories for polymer properties of any kind were, in fact, addressed to the phenomenon of rubber-like elasticity. 

Guth E, James HM (1941) Elastic and thermodynamic properties of rubber-like materials a statistical theory. Ind Eng Chem 33 624... 

This chapter is about semidilute solutions, c > c. We learn both thermodynamics and dynamics. The properties of semidilute solutions are drastically different from those of dilute solutions. With a mere tenfold increase in the concentration, the osmotic pressure can easily increase by a factor of several hundred. In the ideal solution, in contrast, the osmotic pressure is proportional to c. Furthermore, the overall chain motion is slow in semidilute solutions because the chains are entangled semidilute solutions of a high-molecular-weight polymer can barely flow. The solutions are highly viscous and may even behave like elastic rubber. 

The above features of rubbery materials have long been known. The quantitative measurements of mechanical and thermodynamic properties of natural and other elastomers go back to 1805 and some of the studies were conducted by luminaries like Joule and Maxwell. The first molecular theory in polymer science dealt with the rubber elasticity (9-12). 

The elastic aftereffect is encountered in solid-like systems with an elastic behavior. The elastic behavior is reversible when the stress is removed, the strain drops gradually to zero, that is, the initial shape of the body is restored, using the energy stored by the elastic element. However, in contrast to true elastic behavior, the elastic aftereffect is thermodynamically irreversible the dissipation of energy takes place in the viscous element. The damping of mechanical oscillations in rubber, caused by harmonic stresses, is the example of a process conforming to the Kelvin model. 

It is the constraints on the freedom of the chain segments, imposed by the cross-links, which are the cause of the elasticity. Early in the nineteenth century an English chemist, John Gough, performed a simple and illuminating experiment. Apply, he said, a strip of rubber to your lips, stretch it sharply, and you will feel a sensation of warmth. Rubber emits heat when stretched, and conversely will contract, and not expand like most other materials, when heated. So, since, as the First Law of Thermodynamics... 

All the powers of the French Academy of Sciences were needed chemical analysis, mechanical analysis, thermodynamics, alchemy, synthesis. But even Berthelot could not really provide much insight. The Laws of Rubber Elasticity were established by Joule, but even the wizards of British physics could not conjure up an explanation. Until the dawning of the molecular age, no real progress was likely on this subject. 

---