Dynamical behavior of a complex fluid near an out-of-equilibrium transition: approaching simple rheological chaos

TL;DR

This study investigates sustained viscosity oscillations in a complex fluid near an out-of-equilibrium transition, revealing diverse dynamics and the influence of spatial effects, with implications for understanding rheological chaos.

Contribution

It provides a detailed experimental analysis of viscosity oscillations and their connection to microstructural changes and spatial effects in complex fluids near a transition.

Findings

Viscosity exhibits sustained oscillations correlated with microstructure.

Diverse dynamical behaviors observed, including possible spatio-temporal effects.

Oscillations do not strictly correspond to 3D chaos, indicating complex underlying dynamics.

Abstract

We report here an extensive study of sustained oscillations of the viscosity of a complex fluid near an out-of-equilibrium transition. Using well defined protocols, we perform rheological measurements of the onion texture near a layering transition in a Couette flow. This complex fluid exhibits sustained oscillations of the viscosity, on a large time scale (500s) at controlled stress. These oscillations are directly correlated to an oscillating microstrutural change of the texture of the fluid. We observe a great diversity of dynamical behavior and we show that there is a coupling with spatial effects in the gradient v direction. This is in agreement with a carefull analysis of the temporal series of the viscosity with the dynamical system theory. This analysis indicates that the observed dynamical responses do not strictly correspond to 3-dimensional chaotic states, probably because some spatio-temporal effects are present and are likely to play an important role.