Inducing Nematic Ordering of Cellulose Nanofibers using Osmotic Dehydration

Abstract

The formation of nematically-ordered cellulose nanofiber (CNF) materials with an order parameter fmax ≈ 0.8 is studied by polarized optical microscopy, small-angle x-ray scattering (SAXS), and rheological measurements as a function of CNF concentration. The wide range of CNF concentrations, from 0.5 wt% to 4.9 wt%, is obtained using osmotic dehydration with poly(ethylene glycol). The rheological measurements show a strong entangled network over all the concentration range whereas SAXS measurements indicate that at concentrations >1.05 wt% the CNF suspension crosses an isotropic-anisotropic transition that is accompanied by a dramatic increase of the optical birefringence. The resulting nanostructures are modelled as mass fractal structures that converge into co-existing nematically-ordered regions and network-like regions where the correlation distances decrease with concentration. The use of rapid, upscalable osmotic dehydration is an effective method to increase the concentration of CNF suspensions while partly circumventing the gel formation. The facile formation of highly ordered fibers can result in materials with interesting macroscopic properties. with the flow field orientation of cellulose as there is also a unidirectional removal of water. OD has been widely used to dehydrate food at industrial level, 15,16 desalination, purification and biofuel separation and it shares. 17