The viscosity radius in dilute polymer solutions: Universal behaviour from DNA rheology and Brownian dynamics simulations

TL;DR

This study investigates the universal behavior of the viscosity radius in dilute polymer solutions through experiments on DNA and Brownian dynamics simulations, revealing how solvent quality influences polymer swelling.

Contribution

It provides the first combined experimental and simulation analysis of the viscosity radius and universal viscosity ratio for DNA, demonstrating universal crossover behavior across solvent qualities.

Findings

Universal crossover from $ heta$ to good solvents observed

Simulations agree with experimental measurements

Hydrodynamic interactions cause differences between static and dynamic swelling

Abstract

The swelling of the viscosity radius, $\alpha_\eta$, and the universal viscosity ratio, $U_{\eta R}$, have been determined experimentally for linear DNA molecules in dilute solutions with excess salt, and numerically by Brownian dynamics simulations, as a function of the solvent quality. In the latter instance, asymptotic parameter free predictions have been obtained by extrapolating simulation data for finite chains to the long chain limit. Experiments and simulations show a universal crossover for $\alpha_\eta$ and $U_{\eta R}$ from $\theta$ to good solvents in line with earlier observations on synthetic polymer-solvent systems. The significant difference between the swelling of the dynamic viscosity radius from the observed swelling of the static radius of gyration, is shown to arise from the presence of hydrodynamic interactions in the non-draining limit. Simulated values of $\alpha_\eta$ and $U_{\eta R}$ are in good agreement with experimental measurements in synthetic polymer solutions reported previously, and with the measurements in linear DNA solutions reported here.