The
viscosities of semiflexible polymers with different chain stiffnesses
in shear flow are studied via nonequilibrium molecular dynamics techniques.
The simulation reproduces the experimentally observed results, giving
a complete picture of viscosity as chain stiffness increases. Analysis
of flow-induced changes in chain conformation and local structure
indicates two distinct mechanisms behind a variety of viscosity curves.
For polymers of small stiffnesses, it is related to flow-induced changes
in chain conformation and, for those of large stiffnesses, to flow-induced
instabilities of nematic structures. The four-region flow curve is
confirmed for polymers of contour length close to persistence length
and understood by combining the two structural mechanisms. Thus, these
findings clarify the microscopic structures indicated by the macroscopic
viscosity
