Multiple regimes of deformation in shearing flow of isolated polymers

Abstract

Using Brownian dynamics simulations, without excluded volume and hydrodynamic interactions, on single polymer molecules represented by bead-spring models with stiff Fraenkel springs mimicking a single Kuhn step, we find multiple nonlinear regimes of deformation in shear flows that are controlled by the Peclet number (Pe), which is the shear rate times the relaxation time of a Kuhn step. We observe that, for all chain lengths investigated, the average stretch in the flow direction initially increases with increasing Pe, followed by saturation in chain stretch, as observed in previous studies. At even higher Pe, the stretch begins to decrease with increasing shear rate, in accordance with similar simulations of Sendner and Netz, Eur. Phys. J. E 30, 75-81 (2009). At these rates, the trajectories reveal "premature" recoiling of the chain before attaining a fully extended state during the phase of the "tumbling orbit" in which the chain is stretching. An increasing stretch at even higher Pe is characterized by peculiar orientation "locking" effects that may be sensitive to modeling details. We also show that the stretch predictions of coarse-grained springs agree well with those of the fine-grained chains until high shear rates are reached, where the flow perturbs the individual springs from equilibrium. (C) 2012 The Society of Rheology. [DOI: 10.1122/1.3679461]