Polymer Collapse

Abstract

In this chapter we look at the soft polymer (studied in Chapters 3-4) and add to the penalty for self-intersections a reward for self-touchings, i.e., a negative energy is associated with contacts between any two monomers that are not connected to each other within the polymer chain. This is a model of a polymer in a poor solvent: when the polymer does not like to make contact with a solvent it is immersed in, it tries to make contact with itself in order to push out the solvent. An example is polystyrene dissolved in cyclohexane. At temperatures above 35 degrees Celsius the cyclohexane is a good solvent, at temperatures below 30 it is a poor solvent. When cooling down, the polystyrene undergoes a transition from a “random coil” to a “compact ball” (see e.g. S.-T. Sun, I. Nishio, G. Swislow and T. Tanaka [287] and S.F. Sun, C.-C. Chou and R.A. Nash [286]).