ABSTRACT
Rubber is elastic and Gooey liquids such as raw eggs are viscoelastic. Polymeric materials have these rubbery behaviors because chain molecules have many conformations of nearly equal energy and because stretching chains lowers their conformational entropy. Polymer chain entropies and energies also play key roles when proteins fold, when Deoxy Ribonucleic Acid (DNA) becomes encapsulated within virus heads, when DNA wraps around histone proteins, and when polymer gels expand or contract. The simplest molecular description of polymer elasticity and entropy is the random-flight model. One of the most important models is the random-flight theory, in which the distribution of chain end distances is Gaussian. The steric tendency to expand is just balanced by the selfattraction energy causing the chain to contract. When the solvent is poor, the self-attractions between the chain monomers dominate and chains collapse to compact configurations. When the solvent is good, the self-attractions are weak and chains expand more than would be predicted by the random-flight theory.
