In-situ X-ray scattering observation of colloidal epitaxy at the gas-liquid-solid interface

The convective self-assembly of dip-coating is a long-established technique widely employed in scientific and industrial applications. Despite its apparent importance, many of the fundamental aspects remain unknown, particularly the exact assembling mechanism and its relationship with evaporation kinetics and fluid dynamics. Here, we perform the in-situ small-angle X-ray scattering study of the real-time convective self-assembly of colloidal particles inside a meniscus. This approach allows us to resolve the transient assembling processes occurring at the gas, liquid and solid interfaces. Together with ex-situ scanning electron microscopy measurements via the freeze-dry method, the colloidal epitaxy process is uncovered, where the multilayer is sequentially assembled using the interfacial monolayer as a template. The microscopic ordering of the final multilayer is highly correlated with that of the initial monolayer. The evaporation kinetics and fluid dynamics are numerically simulated, which rationalizes the monolayer formation and the dynamic epitaxial process.