10. Revealing the nanoscale organization of cellulose within transparent wood using Scanning Electron Diffraction

Cellulose is the primary structural component in wood, creating a highly organized skeletal structure spanning from nano to macroscale in a matrix with hemicellulose and lignin. Understanding the organization of cellulose is essential for comprehending the mechanical properties of native wood and developing cellulose-based biomaterials.
In plants, cellulose forms a monoclinic Iβ crystal structure composed of closely packed glucan chains. This structure diffracts radiation, such as x-rays and electrons, with the strongest reflections being 200, 110, and 1-10, all with scattering angles perpendicular to the extended fiber direction.

In this study, we utilized Scanning Electron Diffraction (SED) to determine the hierarchical organization of cellulose nanofibers in a bio-composite material through diffraction pattern analysis. SED is an emerging electron microscopy technique that uses a highly parallel electron beam scanned in a raster motion across the sample. A pixelated camera records a diffraction pattern for every beam position, and data analysis is later performed post-acquisition by the precise positioning of virtual detectors in diffraction space. New sensitive cameras, combined with low-dose illumination conditions, have enabled characterization of highly beam-sensitive materials. The ability to shape the electron beam diameter to less than 10 nm allows highly localized information from the sample, such as strain, phase, and orientation, to be determined and visualized. The cellulose fibril orientation can be determined in each beam position by measuring the rotation angle of the 200-reflection in every diffraction pattern.