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 ${\dot{\gamma }}^{*}$, the chain remains collapsed and only deforms slightly, while above ${\dot{\gamma }}^{*}$ the globule exhibits unfolding/refolding cycles. Hydrodynamics are crucial: In the free draining case, ${\dot{\gamma }}^{*}$ scales with the globule radius $R$ as ${\dot{\gamma }}^{*}\sim R^{-1}$, while in the presence of hydrodynamic interactions ${\dot{\gamma }}^{*}\sim R$. Experiments on the globular von Willebrand protein confirm the presence of an unfolding transition at a well-defined critical shear rate.