# Dramatic effect of fluid chemistry on cornstarch suspensions: linking particle interactions to macroscopic rheology

## TL;DR

This study demonstrates how changing fluid chemistry, specifically ethanol content, dramatically affects cornstarch suspension rheology by altering particle interactions and surface polymer behavior, transitioning from shear-thickening to shear-thinning states.

## Contribution

It links microscopic particle surface chemistry and adhesion to macroscopic rheological behavior, revealing the impact of fluid composition on suspension properties.

## Key findings

- Ethanol addition transforms suspension from shear-thickening to shear-thinning.
- Maximum polymer solubility correlates with increased microscopic adhesion and yield stress.
- Fluid chemistry critically influences the suspension's macroscopic rheology.

## Abstract

Suspensions of cornstarch in water exhibit strong dynamic shear-thickening. We show that partly replacing water by ethanol strongly alters the suspension rheology. We perform steady and non-steady rheology measurements combined with atomic force microscopy to investigate the role of fluid chemistry on the macroscopic rheology of the suspensions and its link with the interactions between cornstarch grains. Upon increasing the ethanol content, the suspension goes through a yield-stress fluid state and ultimately becomes a shear-thinning fluid. On the cornstarch grain scale, atomic force microscopy measurements reveal the presence of polymers on the cornstarch surface, which exhibit a co-solvency effect. At intermediate ethanol content, a maximum of polymer solubility induces high microscopic adhesion which we relate to the macroscopic yield stress.