  Spatial configurations of randomly charged polymers, known as polyampholytes
(PAs), are very sensitive to the overall excess charge Q. Analytical arguments,
supported by Monte Carlo simulations and exact enumeration studies, lead to the
following picture: For Q < Q_c = q_0 N^2 (q_0 is the elementary charge, N is
the number of monomers in the polymer), the radius of gyration R_g of the
polymer decreases with decreasing temperature T and the polymer becomes
compact, while for Q>Q_c the polymer stretches with decreasing T. At low T, the
dense states are described by Debye-Huckel theory, while the expanded states
resemble a necklace of globules connected by strings. At such temperatures, the
transition between the dense and the expanded states with increasing Q, is
reminiscent of the breakup of a charged drop.
