Point force manipulation and activated dynamics of polymers adsorbed on structured substrates

Abstract. -We study the activated motion of adsorbed polymers which are driven over a structured substrate by a localized point force. Our theory applies to experiments with single polymers using, for example, tips of scanning force microscopes to drag the polymer. We consider both flexible and semiflexible polymers, and the lateral surface structure is represented by double-well or periodic potentials. The dynamics is governed by kink-like excitations for which we calculate shapes, energies, and critical point forces. Thermally activated motion proceeds by the nucleation of a kink-antikink pair at the point where the force is applied and subsequent diffusive separation of kink and antikink. In the stationary state of the driven polymer, the collective kink dynamics can be described by a one-dimensional symmetric simple exclusion process. Introduction. -The thermally activated escape over potential barriers under the influence of an external force has been first solved by Kramers for a point particle In all of these previous studies, the thermally activated motion is induced by spatially uniform forces which are applied to the whole polymer or elastic line. In contrast, in the present article, we will address the thermally activated motion of polymers over potential barriers in the presence of a point force which acts only locally on the polymer. We will consider both flexible and semiflexible polymers. Our theoretical study is motivated by experimental advances in the manipulation and visualization of single polymers using optica