Viscoelasticity and shear flow of concentrated, non-crystallizing colloidal suspensions: Comparison with Mode-Coupling Theory

TL;DR

This study investigates the viscoelastic and flow properties of concentrated, non-crystallizing colloidal suspensions with adjustable volume fractions, demonstrating that Mode-Coupling Theory accurately describes their rheological behavior across wide ranges of shear rates and frequencies.

Contribution

It provides the first comprehensive experimental validation of Mode-Coupling Theory for concentrated colloidal suspensions with tunable volume fractions and suppressed crystallization.

Findings

Mode-Coupling Theory accurately predicts flow curves and viscoelastic moduli.

Rheological measurements span over 9 orders of magnitude in moduli and 8 in shear rates.

Suspensions show no crystallization due to polydispersity, allowing study near the glass transition.

Abstract

We present a comprehensive rheological study of a suspension of thermosensitive particles dispersed in water. The volume fraction of these particles can be adjusted by the temperature of the system in a continuous fashion. Due to the finite polydispersity of the particles (standard deviation: 17%), crystallization is suppressed and no fluid-crystal transition intervenes. Hence, the moduli $G'$ and $G"$ in the linear viscoelastic regime as well as the flow curves (shear stress $\sigma(\dot{\gamma})$ as the function of the shear rate $\dot{\gamma}$) could be measured in the fluid region up to the vicinity of the glass transition. Moreover, flow curves could be obtained over a range of shear rates of 8 orders of magnitude while $G'$ and $G"$ could be measured spanning over 9 orders of magnitude. Special emphasis has been laid on precise measurements down to the smallest shear rates/frequencies. It is demonstrated that mode-coupling theory generalized in the integration through transients framework provides a full description of the flow curves as well as the viscoelastic behavior of concentrated suspensions with a single set of well-defined parameters.