Influence of dispersion medium structure on the physicochemical properties of aging colloidal suspensions investigated using the synthetic clay Laponite

TL;DR

This study investigates how the structure of the dispersion medium, especially hydrogen bonding, influences the aging and physicochemical properties of colloidal suspensions of Laponite, revealing medium structure's critical role beyond electrostatics.

Contribution

It introduces a novel approach to modify water structure in colloidal suspensions and demonstrates the significant impact of medium structure on aging dynamics, independent of electrostatic interactions.

Findings

Medium structure strongly affects aging when electrostatic interactions are weak.

Hydrogen bond enhancement accelerates suspension aging.

Disruption of hydrogen bonds delays suspension aging.

Abstract

Hypothesis: Aging in colloidal suspensions manifests as a reduction in kinetic freedom of the colloids. In aqueous suspensions of charged colloids, the role of inter-particle electrostatics interactions on the aging dynamics is well debated. Despite water being the dispersion medium, the influence of water structure on the physicochemical properties of aging colloids has never been considered before. Laponite, a model hectorite clay, could be used to evaluate the relative contributions of medium structure and electrostatics in determining the physicochemical properties of aging colloidal suspensions. Experiments: The structure of the dispersion medium is modified either by incorporating uncharged/charged kosmotropic (structure-inducing) or chaotropic (structure-disrupting) molecules or by changing suspension temperature. A new protocol, wherein the medium is heated before adding clay particles, is also introduced to evaluate the effects of hydrogen bond disruptions on suspension aging. Dynamic light scattering, rheological measurements and particle-scale imaging are employed to evaluate the physicochemical properties of the suspensions. Findings: A strong influence of medium structure is evident when inter-particle electrostatic interactions are weak. Enhancement and disruption of hydrogen bonds in the medium are, respectively, strongly correlated with acceleration and delay of suspension aging dynamics. The physicochemical properties of charged clay colloidal suspensions are therefore controlled by altering hydrogen bonding in the dispersion medium.