Screening by symmetry of long-range hydrodynamic interactions of polymers confined in sheets

TL;DR

This paper demonstrates that in sheet-like confinements, the symmetry of 2D flow screens long-range hydrodynamic interactions, leading to Rouse-like polymer dynamics despite the presence of long-range forces.

Contribution

It reveals that symmetry-induced screening causes long-range hydrodynamic interactions to vanish, explaining Rouse-like scaling in confined polymers.

Findings

Hydrodynamic interactions are long-range but effectively screened by symmetry.

Polymer dynamics in sheets follow Rouse scaling, not Zimm.

Screening validates the non-interacting blobs model for confined polymers.

Abstract

Hydrodynamic forces may significantly affect the motion of polymers. In sheet-like cavities, such as the cell's cytoplasm and microfluidic channels, the hydrodynamic forces are long-range. It is therefore expected that that hydrodynamic interactions will dominate the motion of polymers in sheets and will be manifested by Zimm-like scaling. Quite the opposite, we note here that although the hydrodynamic forces are long-range their overall effect on the motion of polymers vanishes due to the symmetry of the two-dimensional flow. As a result, the predicted scaling of experimental observables such as the diffusion coefficient or the rotational diffusion time is Rouse-like, in accord with recent experiments. The effective screening validates the use of the non-interacting blobs picture for polymers confined in a sheet.