Dragging a polymer in a viscous fluid: Steady state and transient

We study the conformation and dynamics of a single polymer chain that is pulled by a constant force applied at its one end with the other end free. Such a situation is relevant to the growing technology of manipulating individual macromolecules, which offers a paradigm research for probing far-from-equilibrium responses of long flexible biological polymers. We first analyze the Rouse model for the Gaussian chains for which the exact analytical results can be obtained. More realistic features such as the finite extensibility, the excluded volume, and the hydrodynamic interactions are taken into account with the help of the scaling argument, which leads to various nontrivial predictions such as the force-dependent friction constants. We elucidate (i) generalized dynamical equations of state describing extension and friction laws in steady-state and (ii) the tension propagation laws in the transient process. We point out that the time evolutions of the dynamic friction in the transient process crucially depend on the experimental protocol, i.e., either constant force or constant velocity ensemble. These predictions could be verified in experiments using giant DNAs and chromosomes.