Counterion-mediated intra-chain phase segregation on a single semiflexible polyelectrolyte chain

The intra-chain phase segregation of coil and globule states was recently found in a single polyelectrolyte. In past literatures, Rayleigh instability upon a charged condensation has been adopted to explain this phenomenon, under the framework of no salt. We considered here the model of a single semiflexible polyelectrolyte such as DNA in a salt solution, and found that the explanation based on Rayleigh instability is inadequate. Instead, this segregation is induced by the instability associated with the translational entropy of counterions. The stability of a segregated chain is enhanced at a lower salt concentration or at a higher temperature. The expected temperature dependence is opposite to that caused by Rayleigh instability.