Unwinding globules under tension and polymer collapse

Polymer collapse is known to be mediated by the formation of pearls. These intermediate structures behave as small globules under tension. The globule size is studied by molecular dynamic simulations as a function of the strength of an external stretching force applied to its ends, for different values of the chain length. A very strong first-order-like transition from a compact globule state to a stretched one is observed. A model of this transition in terms of a globule-chain system is presented. The critical force, above which the globule unwinds, is shown to satisfy a power law scaling like N-1/3 in the number of monomers.