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
