Elasticity entropy-driven

The main models are described in a review by Vrhovski and Weiss [8]. For ideal elastomers in the extended mode, all the energy resides on the backbone and can therefore be recovered upon relaxation [18]. Generally, it is believed that the mechanism of elasticity is entropy-driven, thus the stretching decreases the entropy of the system and the recoil is then induced by a spontaneous return to the maximal level of entropy [8]. 

E. A. Evans and W. Rawicz, "Entropy-driven tension and bending elasticity in condensed-fluid membranes," Phys. Rev. Lett., 64, 2094-7 (1990) E. A. Evans, "Entropy-driven tension in vesicle membranes and unbinding of adherent vesicles," Langmuir, 7, 1900-8 (1991). 

Evans, E. and Rawicz, W. (2094) 1990) Entropy-driven tension and bending elasticity in condensed-fluid membranes. Physical Review Letters, 64 (17), 2097. 

E. Evans and W. Rawicz, Phys. Rev. Lett., 64, 2094 (1990). Entropy-Driven Tension and Bending Elasticity in Condensed-Fluid Membranes. 

Elastomeric materials are uniquely soft, highly stretchable and elastic structures. The synthetic elastomers are linear block copolymers containing soft amorphous sections that provide stretch and hard crystalline components that act as tie points and hold the structure together in an entropy-driven... 

The statistical mechanical theory for rubber elasticity was first qualitatively formulated by Werner Kuhn, Eugene Guth and Herman Mark. The entropy-driven elasticity was explained on the basis of conformational states. The initial theory dealt only with single molecules, but later development by these pioneers and by other scientists formulated the theory also for polymer networks. The first stress—strain equation based on statistical mechanics was formulated by Eugene Guth and Hubert James in 1941. 

Figure 3.3 Entropy-driven elasticity of rubber materials.

The elasticity of rubbers is predominantly entropy-driven which leads to a number of spectacular phenomena. The stiffness increases with increasing temperature. Heat is reversibly generated as a consequence of an applied elastic force and stretching. 

The fundamental driving force behind the remarkable elastic properties of the elastin polymer is believed to be entropic, where stretching decreases the entropy of the system and elastic recoil is driven by a spontaneous return to maximum entropy. The precise molecular basis for elasticity has not been fully elucidated and a number of models exist. Two main categories of structure-function models have been proposed those in which elastin is considered to be isotropic and devoid of structure, and those which consider elastin to be anisotropic with regions of order (Vrhovski and Weiss, 1998). 

The process of protonation allows reconstitution of hydrophobic hydration to such an extent that the temperature range for hydrophobic association drops below that of the operating temperature (Urry, 1993, 1997). The result is a contraction due to hydrophobic association. Again, during an isometric contraction (this time chemically driven), hydrophobic hydration becomes less ordered bulk water. The solvent entropy increases during the development of entropic elastic force due to a decrease in entropy. 

EXAMPLE 9.3 The thermodynamics of a rubber band. Is the retraction of a rubber band driven by a change in enthalpy or in entropy The answer to this question will help us to construct a model for the microscopic behavior of polymeric materials in Chapter 29. Suppose you apply a quasi-static stretching force that increases the length of a rubber band. The force of retraction / exerted by the rubber band is equal and opposite to the applied stretching force. To deal with elastic forces when there is no particle exchange, we have U = U S,VJ) and... 

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