Magnetic field effects on cellulose nanocrystal ordering in a non-aqueous solvent

Cellulose nanocrystals (CNCs) are rod-shaped particles that can self-assemble into a chiral nematic phase at certain contents. Due to their negative diamagnetic susceptibility and high aspect ratio, the structure of the chiral nematic phase of CNC suspensions can be manipulated using a magnetic field, which is a promising path to extending local order to a larger scale. The ability to manipulate CNCs in non-aqueous solvents is critically needed to incorporate them in a wide range of polymers. So far, magnetic field-induced manipulation of CNCs in suspension was reported for aqueous suspensions only, whereas a much-needed similar study for non-aqueous solvents has not been reported to the best of our knowledge. In this paper, we investigate the CNC ordering in n-methylformamide (NMF) under a 0.7 T magnetic field and compare it to the order achieved in H₂O. The formation of a well-defined chiral nematic phase and its viscosity have a significant influence on the rate and extent of the field-induced orientation of CNCs. A clearly formed chiral nematic phase has a high potential for increased levels of field-induced ordering. And the chiral nematic phase with the lowest viscosity showed the largest increase in ordering when the magnetic field is applied before reaching equilibrium and plateauing. In contrast, the higher viscosity suspensions exhibited limited temporal changes after the initial field effect. These findings will facilitate the fabrication of globally ordered CNCs in a variety of polymers under a magnetic field, which is a necessary step to expanding the engineering applications of large-scale cellulose-based composites with anisotropic properties.