Decoupling Structure and Elasticity in Colloidal Gels Under Isotropic Compression

TL;DR

This study investigates how colloidal gel microstructure and elasticity can be independently controlled during isotropic compression, revealing that mechanical response depends solely on volume fraction while microstructure retains memory of initial conditions.

Contribution

It demonstrates that microstructure and elasticity in colloidal gels can be decoupled, challenging existing paradigms and enabling independent tuning of structural and mechanical properties.

Findings

Young modulus and yield stress increase monotonically with volume fraction

Microstructure retains memory of initial state and compression pathway

Mechanical response depends only on volume fraction, not history

Abstract

We exploit the controlled drying of millimeter-sized gel beads to investigate isotropic compression of colloidal fractal gels. Using a custom dynamic light scattering setup, we demonstrate that stresses imposed by drying on the bead surface propagate homogeneously throughout the gel volume, inducing plastic rearrangements. We find that the Young modulus and yield stress of the gels increase monotonically with the instantaneous colloid volume fraction, $\phi$, exhibiting a mechanical response that depends solely on $\phi$, regardless of the drying history. In striking contrast, small-angle X-ray scattering reveals that the gel microstructure retains a strong memory of its initial state, depending on both $\varphi$ and the entire compression pathway. Our findings challenge the prevailing paradigm of a one-to-one relationship between microstructure and elasticity in colloidal fractal gels, opening new avenues for independent control over the structural and mechanical properties of soft materials.