Conformational Phase Transition of a Polyampholyte in a Low Dielectric Solvent

The Debye-Hückel theory augmented by Bjerrum's ideas of dipole formation and Flory's affine network theory of rubber elasticity is applied to the study of neutral polyampholytes (PAs), polymers that in addition to neutral monomers contain charged groups. It is shown that, in the low-temperature state, a PA with N monomers resembles an affine network, or a microgel, and has a radius of gyration which scales as N v , with v = 2/5. As the temperature is raised, a PA undergoes a first-order collapse transition into a dilute globular state in which v = 1/3. The value of the transition temperature is calculated numerically as a function of polymer size. It is argued that this transition should be observable in a low dielectric solvent.