Anisotropic de Gennes narrowing in confined fluids

TL;DR

This study investigates how dense fluids behave when confined in microfluidic channels, revealing anisotropic collective diffusion and slower relaxation compared to bulk fluids, which is crucial for developing microscopic theories.

Contribution

It provides the first experimental evidence of anisotropic de Gennes narrowing in confined dense fluids using combined x-ray techniques.

Findings

Structural relaxation is slower in confinement.

Collective dynamics depend on wave vector and are anisotropic.

De Gennes narrowing observed in confined geometries.

Abstract

The collective diffusion of dense fluids in spatial confinement was studied by combining high-energy (21 keV) x-ray photon correlation spectroscopy and small-angle x-ray scattering from colloid-filled microfluidic channels. We found the structural relaxation in confinement to be slower compared to bulk. The collective dynamics is wave vector dependent, akin to de Gennes narrowing typically observed in bulk fluids. However, in stark contrast to bulk, the structure factor and de Gennes narrowing in confinement are anisotropic. These experimental observations are essential in order to develop a microscopic theoretical description of collective diffusion of dense fluids in confined geometries.