Use of ultrasound attenuation spectroscopy to determine the size distribution of clay tactoids in aqueous suspensions

TL;DR

This study employs ultrasound attenuation spectroscopy to analyze clay suspension particle sizes, revealing that tactoids often remain intact rather than dispersing into individual platelets, challenging previous assumptions.

Contribution

It introduces a novel application of ultrasound attenuation spectroscopy to determine clay tactoid sizes and demonstrates their persistence in suspensions at higher concentrations.

Findings

Tactoids are prevalent in clay suspensions at various concentrations.

Ultrasound attenuation spectra can effectively determine particle size distributions.

Clay tactoids resist complete dispersion due to Coulombic repulsion.

Abstract

The dispersion processes of aqueous samples of clay are studied using ultrasound attenuation spectroscopy. The attenuation spectra that are acquired in the frequency range $10-100$ MHz are used to determine the particle size distributions (PSDs) for different concentrations and ages of the clay suspensions. Our analysis, using equivalent spherical diameter (ESD) for circular discs under Stokes drag in samples of concentrations greater than 1.5\% w/v, shows that a substantial fraction of the aggregates in suspension are actually tactoids that are composed of more than one platelet. This is in contrast to the general belief that clay disperses into individual platelets in the concentration range where their suspensions exhibit glassy behavior. We conclude that the incomplete fragmentation of the clay tactoids arises from the rapid enhancement of the inter-tactoid Coulombic repulsion.