# Effective aspect ratio of helices in shear flow

## TL;DR

This study investigates how rigid colloidal helices behave in shear flow, revealing that their effective aspect ratio influences their rotation and alignment, with implications for understanding their dynamics in fluid environments.

## Contribution

The paper introduces geometric and dynamical effective aspect ratios for helices in shear flow and demonstrates their approximate equivalence across various conditions.

## Key findings

- Elongated helices align more with the flow direction.
- Transient axis deflections depend on helix rotation.
- Effective aspect ratios are consistent across parameters.

## Abstract

We report the results of simulations of rigid colloidal helices suspended in a shear flow, using dissipative particle dynamics for a coarse-grained representation of the suspending fluid, as well as deterministic trajectories of non-Brownian helices calculated from the resistance tensor derived under the slender-body approximation. The shear flow produces nonuniform rotation of the helices, similarly to other high aspect ratio particles, such that more elongated helices spend more time aligned with the fluid velocity. We introduce a geometric effective aspect ratio calculated directly from the helix geometry and a dynamical effective aspect ratio derived from the trajectories of the particles and find that the two effective aspect ratios are approximately equal over the entire parameter range tested. We also describe observed transient deflections of the helical axis into the vorticity direction that can occur when the helix is rotating through the gradient direction and that depend on the rotation of the helix about its axis.