| Abstract: | We theoretically investigate non‐Newtonian viscosity and coil deformation of linear and (regular) star polymers in dilute solution subject to large shear rates. A bead‐and‐spring model with preaveraged hydrodynamic interaction, accounting also approximately for good‐solvent expansion, is employed within the Rouse‐Zimm approach. We impose a constraint on the average spring lengths, so as to keep constant the average contour length of the arms under shear: this corresponds to assuming that the springs become increasingly stiffer. For any topology and a very large molecular mass, coil deformation modifies the hydrodynamic interaction, that goes to a maximum, and then decreases with a crossover from the Zimm to the Rouse regime with increasing shear rate. Correspondingly, the intrinsic viscosity decreases and then raises above its low‐shear value. This behavior is however much less pronounced under good‐solvent conditions. At very large shear rate, the constraint on the spring lengths becomes the dominant factor. This leads to a decrease of intrinsic viscosity with an asymptotic –2/3 power law for any draining condition. Simultaneously, the strongly elongated coil becomes fully aligned with flow. |
