Evaporation-Induced Stratification in Nanoparticle Coatings: A Panoramic Overview of Single-Step Processes to Manufacture Multifunctional Films

Stratification in colloid and polymer films provides an efficient route for producing layered materials through a single-step process. This review gives a brief overview of key mechanisms influencing stratification, with a focus on practical aspects of how these phenomena can be exploited in processing to create desired structures. We additionally describe the diverse morphologies that have been reported, such as large-on-top, small-on-top, and sandwich structures, due to variations in evaporation rate, particle size ratio, and volume fraction. Finally, we discuss how in situ and depth-resolved characterization techniques, such as microbeam SAXS and cryo-SEM, reveal layering within these systems. Computational methods including dynamic density functional theory, explicit-solvent molecular dynamics, and hybrid models address additional complexities. Although each technique has limitations, combining experiments with multiscale simulation studies has greatly expanded our understanding of stratification. Recommendations for future research include energy and biomedical applications and further exploration of complex particle designs.