Supplemental Material

See the supplementary material for more detailed methods, the definition of the radius of NPs, the immersion depth of NP in water, and the areal packing density of carboxyl groups at the NP-water interface. It further covers the nature of the Au-core (solid or hollow), the effect of gravity, the influence of NP sizes for Aun[S(CH2)7COOH]n and Au812[S(CH2)mCOOH]812, and the impact of carboxylic acid dissociation degree influenced by pH on the wettability of NPs.