Direct measurement of the intermolecular forces confining a single molecule in an entangled polymer solution

TL;DR

This study employs optical tweezers to directly measure the forces confining a single polymer within an entangled polymer solution, confirming key theoretical models and providing detailed insights into the polymer's microscopic environment.

Contribution

It provides the first direct experimental measurement of the confining forces and tube-like constraints on a single polymer in an entangled solution, validating reptation theory predictions.

Findings

Measured a confining tube radius of 0.8 microns, close to predicted 0.5 microns.

Identified three relaxation modes at approximately 0.4, 5, and 30 seconds.

Confirmed the presence of a harmonic potential opposing transverse displacement.

Abstract

We use optical tweezers to directly measure the intermolecular forces acting on a single polymer imposed by surrounding entangled polymers (115 kbp DNA, 1 mg/ml). A tube-like confining field was measured in accord with the key assumption of reptation models. A time-dependent harmonic potential opposed transverse displacement, in accord with recent simulation findings. A tube radius of 0.8 microns was determined, close to the predicted value (0.5 microns). Three relaxation modes (~0.4, 5 and 30 s) were measured following transverse displacement, consistent with predicted relaxation mechanisms.