Electric-Field-Driven Trapping of Polyelectrolytes in Needle-like Backfolded States

Polyelectrolytes with strong counterion couplings are compact at low electric fields but switch to elongated forms at high ones. As yet, little is known from both nanomanipulation experiments and theory about the transition mechanisms between compact and extended states. Here, we systematically address this out-of-equilibrium conversion using molecular dynamics simulations of coarse-grained polyelectrolyte chains of 1000 and 1500 monomers in a salt buffer of about 20 000 and 80 000 charged particles, respectively. We find that compact-to-elongated transitions are smooth and fast in only half of the trajectories. In the other half, the elongation is jammed halfway by the formation of backfolded, needle-like states. These states, which have not been envisioned before, have lifetimes that are orders of magnitude larger than the chain's relaxation time and ought to be detectable with current single-molecule experimental setups.