High-throughput screening of silica nanoparticle aggregates in concentrated aqueous electrolytes

The behaviour of colloidal systems in concentrated electrolytes remains under-examined, despite growing evidence of long-range electrostatic forces in hypersaline conditions. Here, we present a high-throughput experimental study of silica nanoparticle aggregation across 912 unique combinations of salt identity and concentration, extending from dilute concentrations to the aqueous solubility limit of nineteen distinct alkali metal halide and alkali metal polyatomic salts. Turbidity measurements reveal a universal re-entrant trend in colloidal stability; aggregation occurs at low to intermediate salt concentrations before reversing at high concentrations. This behaviour is strongly ion-specific, and we demonstrate a quantitative correlation between the onset of re-dispersion and the average radial charge density of the ions, . To probe the structural origin of this re-entrant behaviour, small-angle neutron scattering measurements were performed, revealing a transition from dense to increasingly open mass fractal aggregates at high salt concentrations, rather than complete re-dispersion to primary particles.