Polymers and Rubber Elasticity: Thermodynamics of Large Dimensional Changes in Amorphous Systems
Polymeric molecules constitute a large fraction of the living material They may be in the form of a single macromolecule dissolved in a suitable fluid, or may exist as a three dimensional topological network swollen — to equilibrium — with the surrounding fluid. In either case, the polymersolvent system constitutes a semi—open thermodynamic system where the solvent molecules of much smaller size may enter or leave the space pervaded by the polymeric molecules. The size of the polymer-solvent system changes upon transport of the solvent. At equilibrium, the size of the polymer-solvent system is determined by the equality of the activity of the solvent in the polymer-solvent system to that in the surrounding region, which in most cases is the pure solvent. The solvent activity depends predominantly on i) the constitution of the polymeric chains and the network, and ii) the thermodynamic interaction between the solvent molecules and the polymer. Presence of solvent in a polymeric network dilates the configurations of the macromolecules constituting the network. On the other hand, the connectivity of the network chains opposes dilation. The balance between these two opposing effects determines the equilibrium degree of swelling of the network.
KeywordsPermeability Entropy Rubber Turkey Macromolecule
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