Cellulose nanomaterials extracted from plants are very attractive due to their intrinsic optical and mechanical properties (e.g., high transparency, large elastic modulus, etc) and the potential novel applications that exploit these features. However, despite the extraordinary intrinsic properties of nanocelluloses at the nanoscopic level, the translation of the properties to the macroscopic level is not straightforward and their mechanical properties remain more than an order of magnitude below the expected values. Developing methods to align the cellulose can result in an increase of the macroscopic properties back to the expected levels.
We use external fields to achieve the assembly of nanocelluloses e.g., cellulose nanocrystals and cellulose nanofibers. Short, stiff, cellulose nanocrystals (CNC) form liquid-crystalline chiral nematic phase in aqueous media beyond a critical concentration but the mechanism through which it occurs leads to numerous micron-sized domains (tactoids) of locally order CNC. This results in films with heterogeneous properties and a typical iridescent rainbow-like appearance. Using an external magnetic field has shown to improve the alignment of the tactoids and induces a perpendicular alignment of CNC with respect to the field direction as a result of the diamagnetic nature of cellulose. Herein, we further tailor this alignment by creating a hybrid with paramagnetic iron oxyhydroxide nanoparticles (FeOx) that change the alignment from perpendicular to parallel. Using small-angle neutron scattering we can follow the changes in the alignment of the individual components, CNC and FeOx, as a function of the applied magnetic field under contrast matched solvents.
Figure 1. Schematic representation of the alignment of CNC, FeOx, and the hybrid CNC-FeOx under an external magnetic field..
We would like to explore the changes in optical properties of the hybrid upon switching of the magnetic field as these materials have the interesting optical properties and potential applications as e.g., active light polarizers in paper displays.
This work was conducted by Valentina Guccini, Sugam Kumar, Yulia Trushkina and Germán Salazar-Alvarez# from Stockholm University together with Christina Schütz from Luxembourg University and Gergely Nagy‡ from Paul Scherrer Institute, Switzerland.
Further information: Guccini et al. ChemRXiv 2019