Colloids dragged through a polymer solution: experiment, theory and simulation

TL;DR

This study investigates the drag force on colloids moving through a DNA solution, revealing deviations from classical theory due to DNA accumulation effects, supported by experiments, a drift-diffusion model, and simulations.

Contribution

It combines experimental measurements with theoretical modeling and simulations to explain non-Newtonian drag behavior in polymer solutions.

Findings

Drag force exceeds predictions from classical viscosity-based models.

DNA accumulates in front of the colloid, reducing behind it.

The drift-diffusion model and simulations accurately reproduce experimental results.

Abstract

We present micro-rheological measurments of the drag force on colloids pulled through a solution of lambda-DNA (used here as a monodisperse model polymer) with an optical tweezer. The experiments show a violation of the Stokes-Einstein relation based on the independently measured viscosity of the DNA solution: the drag force is larger than expected. We attribute this to the accumulation of DNA infront of the colloid and the reduced DNA density behind the colloid. This hypothesis is corroborated by a simple drift-diffusion model for the DNA molecules, which reproduces the experimental data surprisingly well, as well as by corresponding Brownian dynamics simulations.