pH Dependence of Interparticle Coupling for Gold Nanoparticle Assemblies Formation: Electrostatic Attraction and Hydrogen Bonding

With the addition of ω-sulfanylalkanoic or ω -alkyldisulfanylalkanoic acids to sodium-contained aqueous Au colloidal solutions, close-packed self-assembly occurred UV-vis, TEM, solid-state ¹³C NMR, and FT-IR spectra were employed to study the resulting aggregation arrays. The resulting two-dimensional Au assemblies exhibited interparticle coupling via both hydrogen bonding and electrostatic interactions at pH 6. Either acidic (pH 3) or base (pH 11) generated significant three-dimensional close-packed aggregates. It is suggested that electrostatic interactions might lead to the aggregates during the dry-up process in the preparation of TEM samples of the Au nanoparticles capped with COO^- terminals at pH 11. For the acidic solutions (pH 3), coagulation was governed by hydrogen-bonding forces.