The fundamental interactions underlying citrate-mediated chemical stability of metal nanoparticles (NPs),<br>and their surface characteristics dictating particle dispersion/aggregation in aqueous solutions, are largely unclear. Here, we used a newly developed theoretical model to estimate the stoichiometry of citrate molecules chemisorbed onto spherical metallic NPs and define the uncovered solvent-accessible surface area of the NP. Then, we exploited two-body free energy calculations and

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... ed coarse-grained molecular dynamics simulations of citrate-capped metallic NPs in saline solutions to explore an experimentally relevant range of NP charge, as well as the electrolytic medium's ionic strength, a known trigger for aggregation. In this way, we define dispersion state phase diagrams of citrate-capped metal nanocolloids. UV-vis spectroscopy experiments validated our predictions and extended our results to NPs up to 35 nm. Altogether, our results disclose a complex interplay between the particle size, its surface charge density, and the ionic strength of<br>the medium, which ultimately clarifies how these variables impact colloidal stability. <br>