Shear-flow-induced unfolding of polymeric globules

The behavior of a single collapsed polymer under shear flow is examined using hydrodynamic simulations and scaling arguments. Below a threshold shear rate gamma.]{*}, the chain remains collapsed and only deforms slightly, while above gamma.]{*} the globule exhibits unfolding/refolding cycles. Hydrodynamics are crucial: In the free draining case, gamma.]{*} scales with the globule radius R as gamma.]{*} approximately R{-1}, while in the presence of hydrodynamic interactions gamma.]{*} approximately R. Experiments on the globular von Willebrand protein confirm the presence of an unfolding transition at a well-defined critical shear rate.