Understanding Cellulose Nanocrystal Cholesteric Phase by Cryo-TEM

Nanocelluloses extracted from pulps (nanocrystals-CNC and nanofibrils-CNF) are environmentally friendly sourced and biocompatible materials with outstanding properties, like high Young’s modulus, and aspect ratio. CNCs readily self-assemble into a nematic phase in water at low concentrations. These structures are promising for the rheological control of formulated products and as photonic pigments.¹ Despite increasing interest, insights into the arrangement of CNCs and its impact on mechanical and optical properties are scarce. In this contribution, we used Cryogenic-Transmission Electron Microscopy (cryo-TEM), to understand the organization of CNCs with different surface charges (≈0, 0.25, and 1.2 mmol g^-1) in water. The oxidized CNCs were prepared using the method described by Habibi (2006), and images were acquired on a Glacios cryo-TEM (Thermo Fisher Scientific).² Preliminary results shows that the CNC morphology is not affected by the degrees of oxidation. All CNC samples expose a rod-like morphology with diameters of 5-8 nm and lengths of 60-160 nm. Surface charges modulate the organization among nanocrystals, and low charge density CNCs are better distributed over the TEM grid. Surprisingly, highly charged CNCs tend to agglomerated, possibly to reduce the excluded volume.³ To characterize arrangement in more detail and to understand how this influences the nematic phase, a Cryogenic-Electron Tomography study is being carried out.