Probing structural relaxation in complex fluids by critical fluctuations

TL;DR

This paper introduces a novel, non-invasive method to probe the structural relaxation of complex fluids by analyzing critical fluctuations and avoided crossing phenomena, avoiding the need for probe particles.

Contribution

The study presents an alternative to microrheology that leverages critical fluctuation analysis to investigate complex fluid dynamics without doping probes.

Findings

Demonstrates the feasibility of using avoided crossing to study relaxation modes

Provides a non-invasive approach to analyze mesoscopic structures

Offers insights into the dynamic response of complex fluids

Abstract

Complex fluids, such as polymer solutions and blends, colloids and gels, are of growing interest in fundamental and applied soft-condensed-matter science. A common feature of all such systems is the presence of a mesoscopic structural length scale intermediate between atomic and macroscopic scales. This mesoscopic structure of complex fluids is often fragile and sensitive to external perturbations. Complex fluids are frequently viscoelastic (showing a combination of viscous and elastic behaviour) with their dynamic response depending on the time and length scales. Recently, non-invasive methods to infer the rheological response of complex fluids have gained popularity through the technique of microrheology, where the diffusion of probe spheres in a viscoelastic fluid is monitored with the aid of light scattering or microscopy. Here we propose an alternative to traditional microrheology that does not require doping of probe particles in the fluid (which can sometimes drastically alter the molecular environment). Instead, our proposed method makes use of the phenomenon of "avoided crossing" between modes associated with the structural relaxation and critical fluctuations that are spontaneously generated in the system.