DNA stretch during electrophoresis due to a step change in mobility.

We investigate DNA stretching during electrophoresis when the mobility abruptly changes. This is a simplified geometry that produces a nonhomogeneous strain rate over the scale of a single molecule. An effective Weissenberg number (Wi) and Deborah number were identified, and the degree of stretching was examined as a function of these two parameters. The system does not undergo a coil-stretch transition. The finite extensibility of the chains only affects the response if the chain is stretched to a significant fraction of the contour length. The wormlike chain shows a characteristic approach to full extension of Wi(-1/2).