Cyclic Motion of a Grafted Polymer under Shear Flow

The long-time dynamics of a single end-tethered chain under shear flow are studied using molecular and Brownian dynamics simulations of a flexible polymer. As observed in previous experiments with tethered DNA [Phys. Rev. Lett. 84, 4769 (2000)], under a flow sheared at constant rate the chain performs a cyclic motion. But, contrary to what has been previously suggested, a well-defined characteristic period exists and it is clearly revealed in the cross spectra of the chain extension along flow and gradient directions. The main cycling time scales like the time needed to stretch the polymer by convection, being about 10 times the relaxation time of the chain in flow. This coherent recursive motion introduces long memory in the fluid and suggests resonance effects under periodic external forcing.