The behavior of randomly charged polyampholytes against a wide range of the Coulomb coupling parameter Γ (the ratio of the Coulomb energy to thermal energy) is studied with the use of molecular dynamics simulations. Neutral polyampholyte collapses for $\Gamma >1,$ where large volume changes are due to multichain effects. Charged chains reptate significantly in a globule. Polyampholyte with widely extensible bonds condenses to a cubic crystal for $\Gamma \gg 1,$ while that with finitely extensible bonds remains in an imperfectly ordered glass structure. Non-neutral polyampholyte whose charge offset exceeds $\frac{1}{2}{N}^{1/2}$ behaves as polyelectrolyte: it consists of nonoverlapped chains for $\Gamma >1,$ and shrinks to the noncharged polymer regime for $\Gamma <1\mathrm{}$ (N is the number of charged monomers). Condensed counterions on polyampholyte screen the electric field, making non-neutral polyampholyte close to the neutral one. Added salt of comparable charge density as that of the polyampholyte further compactifies it. However, the addition of more salt results in the weakening of the polyampholyte nature and reentrant swelling of non-neutral polyampholyte.

• Received 24 February 2000

DOI:https://doi.org/10.1103/PhysRevE.62.3803