Neutral polyampholyte in an ionic solution.

The behavior of a neutral polyampholyte ~PA! chain with N monomers, in an ionic solution, is analyzed in the framework of the full Debye-Hückel-Bjerrum-Flory ~DHBjF! theory. A PA chain, that in addition to the neutral monomers, also contains an equal number of positively and negatively charged monomers, is dissolved in an ionic solution. For high concentrations of salt and at high temperatures, the PA exists in an extended state. As the temperature is decreased, the electrostatic energy becomes more relevant and at a T5Tu the system collapses into a dilute globular state, or microelectrolyte. This state contains a concentration of salt higher than the surrounding medium. As the temperature is decreased even further, association between the monomers of the polymer and the ions of the salt becomes relevant and there is a crossover from this globular state to a low temperature extended state. For low densities of salt, the system is collapsed for almost all temperatures and exhibits a first-order phase transition to an extended state at an unphysical low temperature. @S1063-651X~96!00712-X#