Collapse of Randomly Self-Interacting Polymers

We use complete enumeration and Monte Carlo techniques to study self-avoiding walks with random nearest-neighbor interactions described by v0qiqj, where qi = ± 1 is a quenched sequence of "charges" on the chain. For equal numbers of positive and negative charges (N+ = N-), the polymer with v0 > 0 undergoes a transition from self-avoiding behavior to a compact state at a temperature θ ≈ 1.2v0. The collapse temperature θ(x) decreases with the asymmetry x = |N+ - N-|/(N+ + N-) and vanishes at x ≈ 0.6. For v0 < 0, a θ-point is present at all x.