Power law viscoelasticity of a fractal colloidal gel

TL;DR

This study investigates the power law viscoelastic behavior of a fractal colloidal gel, linking macroscopic rheology to microscopic structural dynamics using combined light scattering and rheological techniques.

Contribution

It establishes a clear connection between the gel's power law rheology and reversible non-affine microscopic rearrangements, modeled by a Fractional Maxwell model.

Findings

Power law rheology accurately described by a Fractional Maxwell model.

Reversible non-affine rearrangements drive the observed rheological behavior.

Power law behavior persists across different sample ages and rheological tests.

Abstract

Power law rheology is of widespread occurrence in complex materials that are characterized by the presence of a very broad range of microstructural length and time scales. Although phenomenological models able to reproduce the observed rheological features exist, in general a well-established connection with the microscopic origin of this mechanical behavior is still missing. As a model system, this work focuses on a fractal colloidal gel. We thoroughly characterize the linear power law rheology of the sample and its age dependence. We show that at all sample ages and for a variety of rheological tests the gel linear viscoelasticity is very accurately described by a Fractional Maxwell (FM) model, characterized by a power law behavior. Thanks to a unique set-up that couples small-angle static and dynamic light scattering to rheological measurements, we demonstrate that the power law rheology observed in the linear regime originates from reversible non-affine rearrangements and discuss the possible relationship between the FM model and the microscopic structure of the gel.