Editing Polymer physics (section)

==Excluded volume interaction==
The [[ideal chain]] model assumes that polymer segments can overlap with each other as if the chain were a phantom chain.  In reality, two segments cannot occupy the same space at the same time.  This interaction between segments is called the [[excluded volume]] interaction.

The simplest formulation of excluded volume is the self-avoiding random walk, a random walk that cannot repeat its previous path.  A path of this walk of ''N'' steps in three dimensions represents a conformation of a polymer with excluded volume interaction.  Because of the self-avoiding nature of this model, the number of possible conformations is significantly reduced.  The radius of gyration is generally larger than that of the ideal chain.