Interplay between Short- and Long-Range Forces in Self-Assembly of Silver Nanoparticles

One of key challenges to understand nanoparticle assemblies is to obtain a correlation between relevant short- and long-range driving forces and resultant transient/final superlattice structure. We studied the self-assembly of silver nanoparticles in aqueous solutions by utilizing a complementary combination of in situ liquid cell transmission electron microscopy, atomic force microscopy-based dynamic force spectroscopy, and theoretical calculations. Despite the nanoparticles exhibiting instantaneous Brownian motion, our study showed that the dynamic behavior of NPs is correlated with the van der Waals force, sometimes unexpectedly over relatively large particle separations. After the silver nanoparticles assemble into clusters, a delicate balance between the hydration and van der Waals forces results in a distinct distribution of particle separation, which is ascribed to layers of hydrated ions adsorbed on the nanoparticle surface. Our study demonstrated a critical role of the complicated correlation between interparticle forces, enabling the control of particle separation and further tailoring the properties of nanoparticle superlattices.