Entropic stress of grafted polymer chains in shear flow

We analyze the shear response of grafted polymer chains in shear flow via coarse-grained molecular dynamics simulations with an explicit solvent. We find that the solvent flow penetrates into almost the whole brush for mushroom-type brushes but only a few bond distances for dense brushes. In all cases, the external stress on the wall equals the entropic stress associated with the distorted polymer conformations. We find that the external stress increases linearly with shear rate at low rates and sublinearly at high rates. The transition from linear to sublinear scaling occurs where chains react to flow by reorienting. Sublinear scaling with shear rate disappears if the shear rate is nondimensionalized with the effective relaxation time of chain subsegments located in the outer part of the brush that experiences flow.

Automated summary

In this study, we investigate the response of grafted polymer chains in shear flow using molecular dynamics simulations. Our results show that the penetration of solvent flow into the brush depends on the brush type, and the external stress is related to the distorted polymer conformations. At low shear rates, the external stress increases linearly with shear rate, while at high rates, it increases sublinearly.