SOLID FRICTION IN GEL-ELECTROPHORESIS

We study the influence of solid frictional forces acting on polymer chains moving in a random environment. We show that the total reduction in the chain tension resulting from the small friction between a polymer and fixed entanglement points is a steep nonlinear function of the number of entanglements (exponential for stretched chains). Therefore, solid friction can drastically change the dynamics and lead to trapping of long chains with a large number of entanglements. We present explicit results for the decrease of the chain tension in the presence of solid friction forces, for the limiting tension values, and for trapping thresholds for charged chains in an external field. The trapping threshold increases with the decrease of the field strength and/or application of pulsed field sequences as compared to static high fields. Our theoretical results on trapping thresholds are in good agreement with experimental data on DNA electrophoresis. Our model also predicts new nonlinear dependencies for the velocity of charged chains that are dragged through the gel by external forces. We present explicit dependencies of the velocity on charge, external force and polymer length for charged chains in external fields and for chains dragged by external forces that are applied only to chain ends. These dependencies are different in large and small force (field) limits, which correspond to stretched and harmonic chains. The strong mobility on length dependence which correspond to stretched and harmonic chains. The strong mobility on length dependence which results from solid friction forces can serve to separate long linear charged polymers of different molecular weight. (C) 1995 American Institute of Physics.