The individualistic dynamics of entangled DNA in solution

We present the direct visualizations of single, entangled DNA polymers in three flow experiments: relaxation following a rapid shear deformation, steady shear, and startup shear. To evaluate molecular theories, test chains were stained against a background of unstained but otherwise identical chains. To provide a direct link to bulk viscoelasticity, identical preparations were also extensively characterized via mechanical rheometry. The four concentrations studied displayed similar rheological features to synthetic polymers at comparable concentrations and were accordingly classified from semidilute to well-entangled. In entangled solutions, we uncovered two distinct relaxation time scales, with the fast, chain retraction characteristic time, tau(fast) approximate to 10-fold longer than the rotational Rouse time assumed by theoretical models. We also found a high degree of molecular individualism and broad conformational distributions in all experiments at shear rates (gamma) over dot > tau(-1)(fast). This new evidence restricts the applicability of the pre-averaging approximation underlying all closed-form theories developed to date and explains some of the complications in modeling nonlinear flows.