# Structure–dynamics decoupling in soft-colloid suspensions

## TL;DR

This study shows that in soft-colloid suspensions, the link between structure and dynamics breaks down, challenging the traditional view in materials science.

## Contribution

The paper reveals a breakdown of de Gennes narrowing in soft-colloid suspensions, showing structure-independent relaxation dynamics.

## Key findings

- The q-dependent relaxation time in soft-colloid suspensions does not correlate with the structure factor.
- Single-particle elasticity enables relaxation pathways that are independent of the suspension structure.
- This behavior challenges the conventional understanding that structure dictates material properties.

## Abstract

The accepted paradigm in materials science is that the internal structure of a material determines its macroscopic properties. This connection is reflected in the particle dynamics, which are known to become slower at length scales comparable to the mean interparticle distance. This implies that the q-dependent relaxation time, with q the magnitude of the scattering wave vector, correlates with the structure factor of the material. This is known as de Gennes narrowing in simple atomic liquids, and is a behavior also seen in colloidal suspensions, where the quantities at play are more easily accessible experimentally. We here find that this familiar correlation can breakdown for soft-colloid suspensions. In both experiments and simulations, we find that the q-dependent relaxation time of the suspension does not follow the structure factor, but that instead, it remains unchanged relative to the length scale at which it is measured. We justify this unusual behavior by alluding to single-particle elasticity and how this aspect allows additional relaxation pathways for the characteristic time of the suspension to remain unaffected by the suspension structure. Our findings challenge the prevailing wisdom that the structure of a material unequivocally determines its properties.

A material’s internal structure is known to dictate its macroscopic properties through structure-dependent particle dynamics, as exemplified by the so-called de Gennes narrowing. Through experiments and simulations on soft colloid suspensions, the authors reveal a breakdown of this correlation, showing that the q-dependent relaxation time remains unchanged across length scales and that single-particle elasticity facilitates structure-independent relaxation.