| Abstract
| - Small-angle X-ray scattering (SAXS) was used to study the size-dependent two-body solvent-mediatedinterparticle interactions between dodecanethiol-coated gold nanocrystals (2−6 nm in diameter) in dilute toluenedispersions. Using a modified Zimm analysis of concentration-dependent X-ray scattering data, the secondvirial coefficient B2 was measured as a function of nanocrystal diameter and compared to theoretical predictions.The measured values of B2 are more negative than those expected for hard spheres, indicating that interparticleattractions are significant in this system, even though the particles are dispersed in good solvents for theligands. The data can be fit using a square well potential to model the pair interactions with nanocrystalsize-dependent well depths ranging between 0.1 and 0.4 kT and a range of interaction of 30 Å. The interactionpotentials between particles in the larger size range (i.e., >5 nm diameter) are close to those expected froma simple steric stabilization model accounting for the core−core van der Waals attraction modified by anosmotic repulsion between adsorbed chains. Smaller particles, however, exhibited significantly strongerattraction than expected from this simple model, which could possibly be due to decreased ligand surfacecoverage at the smaller nanocrystal sizes.
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