Real-Time Observation of Macroscopic Hierarchical Pattern Formation in a Minimal Chemical System via Reaction-Induced Phase Separation

Spatially periodic patterns have been widely studied in chemical and biological systems, yet the emergence of hierarchical or multiscale architectures remains less explored experimentally, particularly in minimal material frameworks. In this work, it was observed in real time that a simple two-component solution consisting of methyltrimethoxysilane and phytic acid spontaneously forms macroscale hierarchical patterns upon exposure to air. Spectroscopic analyses reveal that chemical reactions initiated by environmental moisture drive sol-gel condensation and reaction-induced phase separation (RIPS), leading to the development of compositionally distinct microdomains. The resulting solid structures exhibit both periodic macroscopic wrinkle patterns and microscale anisotropic textures. The correlation between wrinkle spacing and film thickness suggests mechanical stress relaxation (buckling) during solidification, while the presence of localized contour-like features indicates anisotropic molecular ordering within the segregated domains. These findings show that hierarchical pattern formation can arise from the coupled effects of chemical reaction, phase separation, mechanical confinement, and molecular ordering in a minimal system. This platform provides an experimentally accessible route to study pattern formation mechanisms and may offer a basis for designing self-organized materials with multiscale architectures.