Confining Potential as a Function of Polymer Stiffness and Concentration in Entangled Polymer Solutions

We directly track the tubelike motion of individual fluorescently labeled polymer molecules in a concentrated solution of unlabeled polymers. We use a single molecule wide-field fluorescence microscopy technique that is able to determine characteristic properties of the polymer dynamics, such as the confining potential, the tube diameter, and the Rouse time. The use of synthetic polymers allows us to investigate the confined motion of the polymer chains not only as a function of polymer concentration (mesh size) but also versus the persistence length of the matrix polymers. Although the polymers used have a persistence length much smaller than their contour length, our experimental results lead to a dependence of the tube diameter on both the mesh size and the persistence length, which follows the theoretically predicted relation for semiflexible chains.