An in-situ SAXS approach to probe stratification during drying of inorganic nanoparticle films

Understanding particle motion during drying of colloidal and nanoparticle mixtures can be of great significance to processes such as stratification during film formation. Much of the current research in this field focuses on theory and simulation; however, additional experimental approaches are needed to support these studies. Here, we report a novel way to study film structures by applying an in-situ small angle X-ray scattering (SAXS) approach. We present studies of binary films containing two different sizes of silica particles. Our analysis allows us to probe the difference in particle packing in different layers and at different drying times. Furthermore, we can compare film samples consisting of particles with different initial concentrations and size ratios. Although the sample series presented here is limited, the data demonstrates proof-of-concept of the experimental technique. The method will be beneficial for future studies of structure formation in relatively thick films containing inorganic nanoparticles.