Microstructural understanding of the length and stiffness dependent shear thinning in semi-dilute colloidal rods

TL;DR

This study investigates how the length and flexibility of colloidal rods influence shear thinning in semi-dilute suspensions, combining experiments and theory to better understand their rheological behavior.

Contribution

It introduces a revised theoretical model that accounts for shear-induced dilation and confirms length-dependent shear thinning in colloidal rods through experimental validation.

Findings

Shear thinning depends on rod length and flexibility.

Revised theory accurately predicts shear-induced dilation and orientation.

Experimental data supports length-dependent viscosity behavior.

Abstract

Complex fluids containing low concentrations of slender colloidal rods can display a high viscosity, while little flow is needed to thin the fluid. This feature makes slender rods essential constituents in industrial applications and biology. Though this behaviour strongly depends on the rod-length, so far no direct relation could be identified. We employ a library of filamentous viruses to study the effect of rod size and flexibility on the zero-shear viscosity and shear-thinning behaviour. Rheology and small angle neutron scattering data are compared to a revised version of the standard theory for ideally stiff rods, which incorporates a complete shear-induced dilation of the confinement. While the earlier predicted length-independent pre-factor of the restricted rotational diffusion coefficient is confirmed by varying the length and concentration of the rods, the revised theory correctly predicts the shear thinning behaviour as well as the underlying orientational order. These results can be directly applied to understand the manifold systems based on rod-like colloids and design new materials.