Experimental determination of entropic barrier in topologically frustrated polyelectrolyte dynamics

The dynamics of a guest polyelectrolyte chain inside a polymer matrix has been extensively studied in the past decades and several mechanisms, such as the Ogston model, entropic barrier model, and reptation model, have been proposed to interpret the experimental data. Recent experiments reported in the literature point to a new dynamical regime of non-diffusive localization of the guest molecule due to simultaneously operative multiple entropic barriers. With fluorescence microscopy and single-molecule electrophoresis, we have directly observed this phenomenon and evaluated the magnitude of the effective entropic barrier. In our experiments, YOYO-1 labeled λ-DNA was chosen as the charged guest polymer and poly (acrylamide-co-sodium acrylate) polyelectrolyte hydrogel was used as the host matrix. Both the electric field strength dependence of electrophoresis velocity and the non-uniformity of movement indicated a critical electric field strength, E_critical, needed to activate the motion of localized DNA chain. The entropic barrier deduced from E_critical is of the order of tens of k_BT (depending on the mesh size of the host matrix) and close to theoretically calculated values based on the topological frustrated polymer dynamics.