Probing Preferred Orientation in Cellulosic Materials: Nanocrystals, Wood, and Beyond

Preferred orientation is an inherent property of cellulose in its native biological form and has been an inspiration for material scientists. We demonstrate how to use different scattering techniques, including small- and wide-angle neutron and X-ray scattering, to understand preferred orientation of cellulosic materials at multiple length scales. Cellulose nanocrystals (CNC) can be produced by disintegrating microfibers in plant cell walls using sulfuric acid hydrolysis, which exhibit nematic liquid crystal phase behavior. Owing to the enhancement of the total magnetic moment in the self-assembled nanocrystal stacks, CNC particles can be aligned by weak magnetic fields (~0.5 T) in the nematic phase, and be characterized by using small-angle neutron scattering (SANS).  SANS was also used as a non-invasive probe to quantify cross-sectional size of microfibrils in wood, taking advantage of the dramatic difference in scattering length density between deuterated water and hydrogenous cellulose chains. The oriented fibril crystals serve as an excellent bio-template that can incorporate transition metal ions to form an coordinated open framework. Modeling such complex structures using fiber X-ray diffraction is discussed.