In-situ Atomic Force Microscopy Study of the Nanoparticle Self-assembly at the Liquid Interface

Description

Solid particles can assemble at the interface between two immiscible liquids, thereby reducing the interfacial energy. This phenomenon has drawn much attention in the past two decades owing to the fast development of nanotechnology. It is believed that the use of nanoparticle (NP) self-assembly is a promising method for fabricating large-scale and defect-free 2D and 3D hierarchical functional and structural materials. Moreover, rich behavior is exhibited during the self-assembly process of NPs at the liquid interface owing to complex energy landscapes associated. Therefore, understanding the self-assembly of NPs at the liquid interface is of great interest to both academia and industry. However, the lack of experimental methods to directly image NPs assembled at the liquid interface with good spatial and temporal resolution hinders the understanding of this important phenomenon at the single-particle level. This proposed project will aim to explore the use of in situ atomic force microscopy  (AFM) to directly image the self-assembly process of NPs at the water–oil interface with spatial and temporal resolution. Specifically, we will first put effort into conducting time-resolved AFM on NPs assembled at the water–oil interface in situ. We will then apply time-resolved AFM to a model system including hydrophilic charged NPs and oil-soluble surfactants with opposite polarity. This model system has been demonstrated to be highly tunable and non-equilibrium, thereby exhibiting rich behavior. We will systematically study the adsorption kinetics of NPs to the water–oil interface and the in-plane dynamics of NPs at the water–oil interface.  The successful completion of the proposed project will provide new insights into the self-assembly process of NPs at the liquid interface at the single-particle level, particularly for systems trapped in non-equilibrium states. It will also encourage more researchers to consider the use of AFM to study the self-assembly of various nanomaterials at the liquid interface, including 2D superlattices, 2D polymers, and 2D transition metals, among others. We envision that with the combination of ultra-fast AFM imaging techniques, the in situ liquid interfacial imaging system will ultimately provide exceptional spatial and temporal resolution, thereby enabling us to capture unprecedented details of the self-assembly of nanomaterials at liquid interfaces.