The combination of self-assembly and directed attachment of colloidal nanoparticles (NPs) at fluid interfaces presents a scientifically interesting and technologically important research challenge. Remarkable strides have been made in the synthesis of polyhedral NPs with precisely defined shapes and their self-assembly into highly ordered superstructures. Recent advances by our group and others have revealed intriguing synergies between interfacial self-assembly and directed epitaxial attachment into ordered and connected superstructures. Access to NP superstructures with programmable symmetry opens new opportunities not only to create materials with properties by design but also to investigate how they form.
The basic kinetic and thermodynamic factors governing the interplay of self-assembly and directed-attachment are currently poorly understood; this defines the main motivation for the proposed work. We hypothesize that the key to predicting and creating coupled assemblies with programmable structures lies in understanding and controlling the NP orientation at the fluid interface as well as the nature of multi-particle interactions. The NP orientation at the liquid-liquid interface and subsequent directed attachment is a complex function of the interfacial energies, the shape of the particle, the energetics and dynamics of multi-particle interactions and the coupled dynamics of interfacial NP diffusion, ligand displacement from the NP surface and epitaxial fusion of proximate NPs through exposed facets.
We embrace the challenge of understanding the interrelationships between these processes as an opportunity to closely integrate in-situ X-ray structure analysis with multi-scale theoretical modeling. We pursue a hypothesis-driven collaborative approach with three main objectives that aim to understand: (1) the orientation of isolated particles, (2) the influence of multi-particle interactions, and (3) the role of meso-scale effects of particle and fluid dynamics at liquid interfaces.
Recent insights enabled from in-situ studies of the interrelationship between self-assembly and directed attachment enabled the creation of monolayer assemblies with programmable symmetries (e.g. hexagonal and square). By analogy to atomic 2D systems (e.g., graphene), we see 2D nanocrystal assemblies as a fertile ground for scientific discovery with a clear path towards practical applications