Slow, non-diffusive dynamics in concentrated nanoemulsions

TL;DR

This study investigates the slow, wave-vector dependent dynamics of concentrated nanoemulsions using multispeckle x-ray photon correlation spectroscopy, revealing strain-driven motion with unique relaxation properties.

Contribution

It provides the first detailed measurement of wave-vector dependent dynamics in concentrated nanoemulsions, highlighting strain response and weak droplet volume fraction dependence.

Findings

Relaxation time varies inversely with wave vector.

Intermediate scattering function has a compressed exponential shape.

Steady-state velocity is insensitive to droplet volume fraction.

Abstract

Using multispeckle x-ray photon correlation spectroscopy, we have measured the slow, wave-vector dependent dynamics of concentrated, disordered nanoemulsions composed of silicone oil droplets in water. The intermediate scattering function possesses a compressed exponential lineshape and a relaxation time that varies inversely with wave vector. We interpret these dynamics as strain in response to local stress relaxation. The motion includes a transient component whose characteristic velocity decays exponentially with time following a mechanical perturbation of the nanoemulsions and a second component whose characteristic velocity is essentially independent of time. The steady-state characteristic velocity is surprisingly insensitive to droplet volume fraction in the concentrated regime, indicating that the strain motion is only weakly dependent on the droplet-droplet interactions.