Kinetic Insights into Precursor‐Assisted Soft Sphere Close Packing Revealed by In Situ GISAXS with Implications for Gas Sensing

Abstract Packing of soft spheres, such as micelles, polymer‐grafted particles, and microgels, enables the creation of diverse functional materials. Despite the importance of achieving precise structural control, understanding the kinetics of non‐equilibrium packing in a large‐scale deposition process remains challenging. This study investigates the kinetics of the precursor‐assisted close packing of soft spheres using block copolymer micelles as the sphere model. Adding the inorganic precursor SnCl 4 is crucial for achieving the close packing, which is versatile and provides a robust platform for tailoring mesoporous materials with tunable pore sizes. The kinetics of the close‐packing process are explored by in situ grazing‐incidence small‐angle X‐ray scattering measurements during slot‐die coating. The soft crystallization process shows six distinct stages: dilute dispersion, concentrated dispersion, wet film, structuring wet film, gel film, and glassy film. The close packing develops first in the in‐plane direction with rapid domain growth and then advances in the out‐of‐plane direction. Precursors in the interstitial voids play a key role by mitigating packing frustration and favoring face‐centered cubic (FCC) ordering. The structure finally stabilizes into a well‐ordered FCC structure with large domain sizes. The derived mesoporous SnO 2 features semiconducting properties and enhanced pore connectivity, thus showing superior gas sensing performance toward ethanol.