Elasticity dominantly entropic

As seen in Figure 9B, at fixed extension of the y-irradiation-cross-linked elastic matrix comprised of poly[0.8(GVGVP), 0.2(GEGVP)], protonation of four carboxylates per 100 residues results in development of elastic force. A thermoelasticity characterization of this matrix at low pH gives the same result of dominantly entropic elasticity as found in curve b of Figure 6B for poly(GVGVP) in the absence of carboxyl moieties. 

To extract a value of the step-mobility h from the grating relaxation experiments [12], we must evaluate the strength of the step-step interaction y. Computational work suggests that ydue to elastic interactions between Si(OOl) steps is 0.2 eV run [29], while, we estimate that the entropic interaction is 10 times larger. (We use a step stiffness P calculated from the geometric mean of P for Sa and Sb steps given in Ref [30] P, 0.03 eV mn-. ) Therefore, entropic repulsion should dominate, and... 

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. 

Physically, the temperature rise in a lament must be due to a combination of viscous dissipation and elastic (i.e., entropic) heating the Gough-Joule effect.(D The former is no doubt dominant in the case of fracture of high polymers(40) see below. But it is not possible at present to estimate the proportions of these two causal factors. It is to be expected that their... 

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