Unentangled rubber elasticity

In typical crystalline solids, such as metals, the energetic contribution dominates the force because the internal energy increases when the crystalline lattice spacings are distorted from their equilibrium positions. In rubbers, the entropic contribution to the force is more important than the energetic one. In ideal networks there is no energetic contribution to elasticity, so /e = 0. 

The dominance of the entropic part of Eq. (7.11) bestows a peculiar temperature dependence to the force at constant extension. While crystalline solids have the force decrease weakly with increasing temperature, rubbers show the opposite—behaviour.—The—network strands 

A simple way to separate energetic from entropic contributions to the elastic f rcc was developed by Flory—Consider a typic il fpmppmfnrp f  

A schematic representation of the Flory construction for a polymer network. 

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Elastomer is a general term used for cross-linked polymeric materials such as rubber with elastic properties described above. However, elastomers are not purely elastic materials and they exhibit damping, that is, fractional energy loss per cycle in, say, an oscillatory experiment. The energy loss is due primarily to stress relaxation (viscous dissipation) of inelastic pendant chains and unentangled loops in the network. In the case of a prescribed stress sinusoidal deformation, the applied stress is expressed as... 

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