Nonlinear viscoelasticity of entangled DNA molecules

T4 DNA semi-dilute entangled solutions submitted to high shear rates show a region of weak dependence of the steady-state shear stress on the shear rate. For the highest concentration studied, this region extends over two decades of shear rate, and a plateau of shear stress is observed over one decade. The concentration dependence of the lower boundary of this region scales as the reciprocal of the disengagement time. The concentration dependence of the upper boundary is compatible with the scaling of the reciprocal of the Rouse relaxation time of the entire chain in its tube.