Alignment of colloidal rods in crowded environments

TL;DR

This study investigates how polymer crowding affects the flow-induced alignment of colloidal rods, revealing that polymer dynamics and the Weissenberg number govern alignment behavior, which follows a universal trend regardless of crowding environment.

Contribution

It demonstrates that polymer dynamics control colloidal rod alignment in crowded solutions and introduces a universal trend based on shear rate and polymer deformation.

Findings

Polymer dynamics determine the onset of rod alignment.

Alignment follows a universal trend independent of crowding type.

Critical shear rate predicts colloidal alignment in polymer solutions.

Abstract

Understanding the hydrodynamic alignment of colloidal rods in polymer solutions is pivotal for manufacturing structurally ordered materials. How polymer crowding influences the flow-induced alignment of suspended colloidal rods remains unclear when rods and polymers share similar length-scales. We tackle this problem by analyzing the alignment of colloidal rods suspended in crowded polymer solutions, and comparing against the case where crowding is provided by additional colloidal rods in a pure solvent. We find that the polymer dynamics govern the onset of shear-induced alignment of colloidal rods suspended in polymer solutions, and the control parameter for the alignment of rods is the Weissenberg number, quantifying the elastic response of the polymer to an imposed flow. Moreover, we show that the increasing colloidal alignment with the shear rate follows a universal trend that is independent of the surrounding crowding environment. Our results indicate that colloidal rod alignment in polymer solutions can be predicted based on the critical shear rate at which polymer coils are deformed by the flow, aiding the synthesis and design of anisotropic materials.