An Interferometric Method to Visualize and Quantify Nanofluid Stability

Abstract

Establishing the stability of nanofluids is essential in both laboratory and industrial settings. High stability over time is needed to ensure that the suspensions retain their enhanced properties and provide reliable long-term performance. In the current work, we demonstrate an optical method to visualize and quantify the stability of transparent nanofluids. The time variation of the concentration distribution and the local concentration gradients have been measured in an Al2O3-water nanofluid (ϕ=0.16 wt.%) using a Mach-Zehnder interferometer. A nanofluid prepared using standard two-step methods was found to be unstable over a short time interval, despite having a high zeta potential (43.7 mV). The concentration distribution was predicted using a simple gravitational settling model based on Stokes’ flow combined with particle size distribution measurements from dynamic light scattering (DLS). The results indicate that one of the main causes of the sedimentation instability was the presence of a small number of larger particles, which were detected using DLS analysis.

Keywords: Nanofluid stability, Interferometry, Gravitational settling, Visualization, Sedimentation