Chain dynamics in steady shear flow

Recent experimental measurements of the static and dynamic properties of si ngle fluorescently labeled molecules of DNA in steady shear flow are compar ed with the predictions of a theoretical model of chain dynamics. The model is based on a set of coupled kinetic equations for the evolution of chain conformations and solvent fluctuations. The polymer is represented as a con tinuous curve with no excluded volume or hydrodynamic interactions, while t he solvent is described by a time and space-varying velocity field. In the absence of constraints that enforce the finite extensibility of the chain a t large shear rates, the calculated curves of the normalized dynamic autoco rrelation function of the mean extension reproduce the qualitative features of the measured curves, but otherwise deviate significantly from them. We develop an analytically tractable finitely extensible model of the Gaussian chain that is more successful in reproducing the experimental data. (C) 20 00 American Institute of Physics. [S0021-9606(00)51819-4].