Steady state sedimentation of ultrasoft colloids

TL;DR

This study investigates the sedimentation behavior of ultra-soft star polymers under various external force fields using mesoscale simulations, revealing structural changes and non-linear sedimentation dynamics.

Contribution

It introduces a hybrid simulation approach to analyze how star polymers' structure and sedimentation coefficients vary with external force strength, highlighting non-linear effects.

Findings

Structure remains nearly unchanged in weak fields

Radius of gyration decreases at intermediate fields

Sedimentation coefficient exhibits a maximum at intermediate fields

Abstract

The structural and dynamical properties of ultra-soft colloids - star polymers - exposed to a uniform external force field are analyzed applying the multiparticle collision dynamics approach, a hybrid coarse-grain mesoscale simulation approach, which captures thermal fluctuations and long-range hydrodynamic interactions. In the weak field limit, the structure of the star polymer is nearly unchanged, however in an intermediate regime, the radius of gyration decreases, in particular transverse to the sedimentation direction. In the limit of a strong field, the radius of gyration increases with field strength. Correspondingly, the sedimentation coefficient increases with increasing field strength, passes through a maximum and decreases again at high field strengths. The maximum value depends on the functionality of the star polymer. High field strengths lead to symmetry breaking with trailing, strongly stretched polymer arms and a compact star polymer body. In the weak field linear response regime, the sedimentation coefficient follows the scaling relation of a star polymer in terms of functionality and arm length.