From a cholesteric non-aqueous cellulose nanocrystal suspension to a highly ordered film

A highly ordered cellulose nanocrystal (CNC) film was processed and characterized from a non-aqueous suspension. As a first step, by drawing upon the negative magnetic anisotropy of CNCs, a global order of the nanocrystals is achieved by magnetic field-assisted manipulation of a cholesteric suspension in n-methylformamide (NMF), and then the order is subsequently preserved into a solid-state film. We study the differences between the structures of the 4 T-dried film and the control film dried in the absence of magnetic field. Additionally, we compare the NMF-dried films to those dried from aqueous suspensions with and without magnetic field. Optical microscopy, cross-sectional imaging analysis, and sum frequency generation (SFG) spectroscopy show that the CNC-NMF film dried under magnetic field exhibited a highly ordered layered structure throughout the film, comparable to that observed when films were produced from aqueous suspensions. Extending the potential of the CNC alignment to non-aqueous systems will enable a broad spectrum of applications for CNC-based polymer composites.