Multiscale Visualization of Hierarchical Structures in Filler‐Containing Epoxy Resins via X‐Ray Scattering Computed Tomography

We report multiscale visualization of hierarchical structures in filler‐containing epoxy resins using X‐ray scattering computed tomography (XRS CT). The entire cross‐sections of epoxy samples cured on aluminum substrates, including air‐exposed edges, were analyzed by wide‐, medium‐, and small‐angle XRS CT (WAXS‐, MAXS‐, and SAXS‐CT, respectively) with a spatial sampling of 10 μm. WAXS‐CT revealed q ‐dependent short‐range molecular correlations in the epoxy/amine matrix, whereas MAXS‐CT visualized the spatial distribution of the relative cross‐linked structure density. The low‐ q ‐side WAXS‐derived molecular correlation contrast showed partial spatial consistency with the edge‐enhanced MAXS‐derived network contrast, whereas the peak‐top/high‐ q ‐side WAXS contrast was enhanced mainly in the interior, suggesting q ‐dependent variation in the local molecular environment of the cured network. SAXS‐CT indicated that phenylsilane‐modified silica nanoparticles accumulated near the edges; however, quantitative pixel‐wise correlation analysis showed no meaningful linear correlation and only a very weak monotonic relationship between silica accumulation and the local MAXS‐derived relative cross‐linked structure density. MAXS‐CT also detected edge‐localized CBMA‐derived crystalline domains, most plausibly associated with carbamate salt–like species formed at the air‐exposed interface. These multiscale CT analyses reveal the hierarchical and spatially heterogeneous organization of fillers, network‐related structures, q ‐dependent short‐range molecular correlations, and crystalline domains in cured epoxy composites, providing insights into how air‐exposed curing affects multiscale structure formation.