Lecture 19: Polymer Models: Persistence and Self-Avoidance

As an example of the type of prediction which can be made using this type of simple model, consider the following experiment: Pull on both ends of a polymer and measure the force f required to stretch it out2 . Note that the force will be given by f = −(∂F/∂R) where F = U − TS is the Helmholtz free energy (T is the temperature, U is the internal energy, and S is the entropy). In the simplest random­walk model of a polymer chain, we neglect forces between monomers (and the solvent), aside from the constraint of connecting the monomers in a chain, so there is no internal energy, U = 0. The free energy is thus fully determined by the entropy, S, which essentially