Shear jamming and fragility in fractal suspensions under confinement

TL;DR

This study reveals shear jamming in ultra-dilute fractal suspensions of carbon nanotubes at very low concentrations, demonstrating a direct transition from flow to jammed state without prior shear-thickening, and proposes a generalized phase diagram.

Contribution

It is the first to experimentally demonstrate shear jamming in fractal suspensions at ultra-low concentrations and develops a generalized phase diagram for such systems.

Findings

Shear jamming occurs at ~0.5% volume fraction, much lower than in dense suspensions.

Direct transition from flow to shear jammed state without shear-thickening.

Proposed a generalized phase diagram capturing shear jamming behavior.

Abstract

Under applied stress, the viscosity of many dense particulate suspensions increases drastically, a response known as discontinuous shear-thickening (DST). In some cases, the applied stress can even transform the suspension into a solid-like shear jammed state. Although shear jamming (SJ) has been probed for dense suspensions with particles having well-defined shapes, such a phenomenon for fractal objects has not been explored. Here, using rheology and in situ optical imaging, we study the flow behaviour of ultra-dilute fractal suspensions of multi-walled carbon nanotubes (MWCNT) under confinement. We show a direct transition from flowing to SJ state without a precursory DST in fractal suspensions at an onset volume fraction, $\phi \sim$ 0.5\%, significantly lower than that of conventional dense suspensions ($\phi \sim$ 55\%). The ultra-low concentration enables us to demonstrate the fragility and associated contact dynamics of the SJ state, which remain experimentally unexplored in suspensions. Furthermore, using a generalized Wyart-Cates model, we propose a generic phase diagram for fractal suspensions that captures the possibility of SJ without prior DST over a wide range of shear stress and volume fractions.