Calcium hydroxide forms unstable reactive nanoparticles that are stabilized when they are dispersed in ethylene
glycol or 2-propanol. The aggregation behavior of these particles was investigated by contrast-variation small-angle
neutron scattering (SANS), combined with small-angle X-ray scattering (SAXS). Nanoparticles on the order of 100
nm were found to aggregate into mass-fractal superstructures in 2-propanol, while forming more compact agglomerated
aggregates with surface fractal behavior in ethylene glycol. Commensurate specific surface areas evaluated at the Porod
limit were more than an order of magnitude greater in 2-propanol (200 m2âg-1) than in ethylene glycol (7 m2âg-1).
This profound microstructural evolution, observed in similar solvents, is shown to arise from competitive solvent
adsorption. The composition of the first solvent layer on the particles is determined over the full range of mixed solvent
compositions and is shown to follow a quantifiable thermodynamic equilibrium, determined via contrast-variation
SANS, that favors ethylene glycol over 2-propanol in the surface layer by about 1.4 kJâmol-1 with respect to the bulk
solvent composition.