Probing shear-induced rearrangements in Fourier Space. I. Dynamic Light Scattering

TL;DR

This paper explores how Fourier space methods, specifically dynamic light scattering, can be used to analyze microscopic shear-induced rearrangements in soft matter, distinguishing affine and non-affine displacements through theoretical, numerical, and experimental approaches.

Contribution

It introduces a method to separate affine and non-affine displacements in soft materials using dynamic light scattering coupled with rheology, advancing understanding of microscopic dynamics.

Findings

Dynamic light scattering can distinguish affine from non-affine displacements.

Non-idealities in experiments affect the measurement of microscopic dynamics.

Theoretical, numerical, and experimental results validate the approach.

Abstract

Understanding the microscopic origin of the rheological behavior of soft matter is a long-lasting endeavour. While early efforts concentrated mainly on the relationship between rheology and structure, current research focuses on the role of microscopic dynamics. We present in two companion papers a thorough discussion of how Fourier space-based methods may be coupled to rheology to shed light on the relationship between the microscopic dynamics and the mechanical response of soft systems. In this first companion paper, we report a theoretical, numerical and experimental investigation of dynamic light scattering coupled to rheology. While in ideal solids and simple viscous fluids the displacement field under a shear deformation is purely affine, additional non-affine displacements arise in many situations of great interest, for example in elastically heterogeneous materials or due to plastic rearrangements. We show how affine and non-affine displacements can be separately resolved by dynamic light scattering, and discuss in detail the effect of several non-idealities in typical experiments.