Nanoparticle Assembly and Transport at Liquid-Liquid Interfaces

TLDR

Self‑assembly of particles at fluid interfaces is driven by interfacial energy, but for nanoscopic particles thermal fluctuations create size‑dependent assembly, and fluid interfaces enable rapid equilibrium and easy nanoparticle access for modification. Ligand‑stabilized nanoparticles were assembled into three‑dimensional constructs at fluid‑fluid interfaces while preserving their unique nanoparticle properties. The nanoparticles’ small size weakly confines them at the interface, enabling size‑selective assembly, two‑dimensional phase behavior, and functionalization, while a photoinduced transformation transports them from toluene into water and their fluorescence emission directly probes their spatial distribution.

Abstract

The self-assembly of particles at fluid interfaces, driven by the reduction in interfacial energy, is well established. However, for nanoscopic particles, thermal fluctuations compete with interfacial energy and give rise to a particle-size-dependent self-assembly. Ligand-stabilized nanoparticles assembled into three-dimensional constructs at fluid-fluid interfaces, where the properties unique to the nanoparticles were preserved. The small size of the nanoparticles led to a weak confinement of the nanoparticles at the fluid interface that opens avenues to size-selective particle assembly, two-dimensional phase behavior, and functionalization. Fluid interfaces afford a rapid approach to equilibrium and easy access to nanoparticles for subsequent modification. A photoinduced transformation is described in which nanoparticles, initially soluble only in toluene, were transported across an interface into water and were dispersed in the water phase. The characteristic fluorescence emission of the nanoparticles provided a direct probe of their spatial distribution.