Lift Force and Dynamical Unbinding of Adhering Vesicles under Shear Flow

Abstract

We show that a vesicle under shear flow experiences a lift force of hydrodynamical origin. This force is of purely viscous nature, and it originates from upstream-downstream asymmetry. At a critical shear rate $\ensuremath{\gamma}\ensuremath{\simeq}100--500\mathrm{Hz}$ the vesicle, initially making adhesion with a substrate, undergoes an unbinding transition in two nontrivial steps. In the first step the lift force behaves as ${\ensuremath{\gamma}}^{2}$, whereas in the second step as $\ensuremath{\gamma}$. We present numerical and analytical results on this phenomenon. We discuss several implications.