Electron microdiffraction reveals the nanoscale twist geometry of cellulose nanocrystals

Nanocellulose consisting of crystalline cellulose nanoparticles has high potential to serve as a building block for bio-based functional materials. The intrinsic chirality of cellulose provides them with high added values such as optical properties and chiral induction ability. At the nanoscale, this chirality is connected to the right-handed longitudinal twisting of these fibrous crystallites. However, this nanoscale fibrillar twist has been a matter of debate due to contradictory data between ultrastructural observations and molecular simulations and so far, the exact twist geometry has not been elucidated. Here, an electron microdiffraction (μED) analysis under cryogenic conditions reveals the continuous twisting of cellulose nanocrystals (CNCs) in aqueous suspension. This intrinsic regular twist is drastically modified to a discontinuous sharp twist when the CNCs are dried on a flat surface. The present μED-based analysis at the single nanoparticle level allows the establishment of the quantitative structure-property relationship of various solid and colloidal nanocellulose systems.