CONCENTRATION-DEPENDENT COLLAPSE OF A LARGE POLYMER

The observed condensation of DNA in salt solution in the presence of a second polymer of lower molecular weight is treated by straightforward statistical mechanics. We neglect the details of DNA structure and represent it by a simple polymer of large molecular weight interacting via single-contact repulsive forces with a large number of smaller polymers. In this approximation, the derivative of free energy with respect to the size of the large polymer shows a singularity at a critical concentration of smaller polymers. © 1978 The American Physical Society.