Stretch-relaxation of DNA molecules in semidilute solutions
Several studies of single molecules of fluorescently labeled DNA have been carried out in order to gain insight into the conformational evolution of polymer chains when subjected to a variety of flow fields. These studies have not only enabled the direct visual observation of 'molecular individualism', but have also proven to be of vital importance for the validation of molecular theories of polymer dynamics. Nearly all these investigations have been carried out in either the dilute or concentrated solution regimes, with only a few in the semidilute regime. Given the importance of semidilute polymer solutions, both from a fundamental and a practical point of view, it is essential to gain an understanding of the fundamental physics that govern the dynamics of polymer molecules in this regime. The recent single molecule experiments of Hsiao et al. [J. Rheol., 61, 151–167, 2017] on semidilute polymer solutions of λ-phage DNA undergoing planar extensional flow provide benchmark data which can be used to verify molecular theories for polymer solutions in this regime of concentration. In particular, they examine the response of individual chains to step-strain deformation followed by cessation of flow, thereby capturing both chain stretch and relaxation in a single experiment. In this talk, I will discuss how numerical simulations with a recently developed Brownian dynamics algorithm can lead to quantitatively accurate predictions of the experimental observations in both the stretching and relaxation phases.