Multi-directional neutron dark-field tomography of nanostructural orientation in cellulose foams

Hierarchical biomaterials embody nature's intricate design principles and offer multiple functionalities through the multi-level organization of their molecular and nanosized building blocks. However, 3D structural characterization over length scales ranging from nanometers to centimeters of biopolymer-based materials remains a challenge. Current limitations hinder understanding how macroscopic properties originate in the multiscale arrangement of nanoscale structures that cannot be fully captured from small sample volumes. Here, we demonstrate how multi-directional neutron dark-field tomography (MD-NDFT) provides structural information on multiple length scales in large volumes of heterogeneous hierarchical soft matter materials. By implementing 3D single-grid directional neutron dark-field reconstructions, we quantified the degree of preferential alignment of cellulose nanostructures in centimeter-sized assemblies of several nanocomposite foams simultaneously, probing structural features down to 50 nm through anisotropic ultrasmall-angle scattering, within a field of view ≳ 40 cm 2 . The successful application of MD-NDFT to nanocellulose, which is inherently radiation-sensitive, prevalent in natural systems and widely used in nanotechnology, proves the relevance of MD-NDFT for multiscale characterization of hierarchical biobased and bioinspired materials.