Entropy entropic driving force

The reversible recovery of a deformed elastomer to its original (undeformed) state is due to an entropic driving force. The entropy of polymer chains is minimum in the extended conformation and maximum in the random coil conformation. Cross-linking of an elastomer to form a network structure (IX) is... 

As noted, TPEs are either block copolymers or combinations of a rubber-dispersed phase and a plastic continuous matrix. The attribute contributed by the rubbery phase - such as butadiene or ethylenebutylene in an S-E-S or SEB-S styrenic block copolymer, or the completely vulcanized EPDM rubber particles in a polypropylene (PP)/EPDM EA - is classical elastomeric performance. The elastic properties of a rubber result from long, flexible molecules that are coiled in a random manner. When the molecules are stretched, they uncoil and have a more specific geometry than the coiled molecules. The uncoiled molecules have lower entropy because of the more restricted geometry and, since the natural tendency is an increase in entropy, the entropic driving force is for the molecules to retract. 

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). 

Membrane equilibria give rise to a pressure difference between the two phases. For three-dimensional systems this is the osmotic pressure 77, for two-dimensional systems it is the surface pressure, n. For osmosis the driving force is the fact that the chemical potential of the water is lower on the side containing the molecules that cannot pass the membrane. As a result, water is imbibed and this process continues until the water transport has resulted in a pressure compensating n. The driving force is primarily entropical and stems from the mixing entropy the osmotic pressure follows from see [1.2.12.15],... 

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