# Competing Time Scales Lead to Oscillations in Shear-Thickening Suspensions

## TL;DR

This paper demonstrates that the interaction between instrument inertia and particle contact formation causes shear-rate oscillations in shear-thickening suspensions, revealing new insights into flow behavior and contact dynamics.

## Contribution

It introduces a model linking instrument inertia and contact formation time scales to oscillations, validated by experiments, and provides a method to measure contact relaxation times.

## Key findings

- Oscillations depend on the interplay of two time scales.
- Oscillation frequency measures contact relaxation time.
- Flow curve access is extended beyond conventional rheometry.

## Abstract

Competing time scales generate novelty. Here, we show that a coupling between the time scales imposed by instrument inertia and the formation of inter-particle frictional contacts in shear-thickening suspensions leads to highly asymmetric shear-rate oscillations. Experiments tuning the presence of oscillations by varying the two time-scales validate our model. The observed oscillations give access to a shear-jamming portion of the flow curve that is forbidden in conventional rheometry. Moreover, the oscillation frequency allows us to quantify an intrinsic relaxation time for particle contacts. The coupling of fast contact network dynamics to a slower system variable should be generic to many other areas of dense suspension flow, with instrument inertia providing a paradigmatic example.