Magnetophoresis in the Rubinstein-Duke model

TL;DR

This study investigates the behavior of a reptating polymer under a pulling force at one end using the Rubinstein-Duke model, revealing velocity profiles, density distributions, and non-monotonic link behaviors through extensive calculations.

Contribution

It provides new interpolating formulas for drift velocity and density profiles, and introduces a detailed description of chain behavior under varying pulling forces.

Findings

Velocities and densities follow simple crossover formulas.

Profiles show non-monotonic link densities at high fields.

Distinct head and tail zones depend on the pulling strength.

Abstract

We consider the magnetophoresis problem within the Rubinstein-Duke model, i.e. a reptating polymer pulled by a constant field applied to a single repton at the edge of a chain. Extensive density matrix renormalization calculations are presented of the drift velocity and the profile of the chain for various strengths of the driving field and chain lengths. We show that the velocities and the average densities of stored length are well described by simple interpolating crossover formulae, derived under the assumption that the difference between the drift and curvilinear velocities vanishes for sufficiently long chains. The profiles, which describe the average shape of the reptating chain, also show interesting features as some non-monotonic behavior of the links densities for sufficiently strong pulling fields. We develop a description in which a distinction is made between links entering at the pulled head and at the unpulled tail. At weak fields the separation between the head zone and the tail zone meanders through the whole chain, while the probability of finding it close to the edges drops off. At strong fields the tail zone is confined to a small region close to the unpulled edge of the polymer.