SOLID FRICTION IN GEL-ELECTROPHORESIS

We study the influence of solid frictional forces acting on polymer ch ains moving in a random environment. We show that the total reduction in the chain tension resulting from the small friction between a polym er 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 trappi ng of long chains with a large number of entanglements. We present exp licit results for the decrease of the chain tension in the presence of solid friction forces, for the limiting tension values, and for trapp ing thresholds for charged chains in an external field. The trapping t hreshold increases with the decrease of the field strength and/or appl ication of pulsed field sequences as compared to static high fields. O ur theoretical results on trapping thresholds are in good agreement wi th experimental data on DNA electrophoresis. Our model also predicts n ew nonlinear dependencies for the velocity of charged chains that are dragged through the gel by external forces. We present explicit depend encies of the velocity on charge, external force and polymer length fo r charged chains in external fields and for chains dragged by external forces that are applied only to chain ends. These dependencies are di fferent in large and small force (field) limits, which correspond to s tretched and harmonic chains. The strong mobility on length dependence which correspond to stretched and harmonic chains. The strong mobilit y on length dependence which results from solid friction forces can se rve to separate long linear charged polymers of different molecular we ight. (C) 1995 American Institute of Physics.