Hydrophobic hydration mediated universal self-association of colloidal nanoclay particles

The pH dependent stability of aqueous dispersion of nanoclay particles was examined in a systematic manner spread over a period of 50 days. The results are discussed in terms of relative stability of electrical double layers. Subsequently, unique self-association of nanoclay particles occurring in water–alcohol binary solvents, induced by solvent hydrophobicity, was investigated. The normalized effective size of clusters, (Reff − R0)/R0 and their excess zeta potential, (ZOH − ZW)/ZW were found to scale with alcohol mole fraction, χOH (methyl, ethyl or propyl) as (Reff−R0)/R0∼χOHα and (ZOH−ZW)/ZW∼χOHβ where β = 0.53 ± 0.05, 0.55 ± 0.05 and 0.60 ± 0.06 for binary solvents having methanol, ethanol and propanol respectively, and α ≈ β. The zeta potential and cluster size of nanoclay aggregates in water and the water–alcohol binary solvent are ZW and ZOH and R0 and Reff respectively. The reduced viscosity of the solution was found to scale with alcohol concentration as (ηr−1)∼χOHδ with δ = 0.41 ± 0.05, 0.50 ± 0.05 and 0.59 ± 0.07 for binary solvents having methanol, ethanol and propanol respectively. It was found that solvent hydrophobicity facilitates Laponite association through face-rim electrostatic interactions. Results are discussed in the framework of hydrophobic hydration of alcohol molecules in water which is strongly dependent on alcohol concentration.