Above a critical concentration, aqueous dispersions of sulfonated cellulose nanocrystals (CNC) form chiral nematic liquid crystalline phases. Retention of microstructural order and planar anchoring of the helix during drying should result in films that exhibit selective reflection of specific wavelengths of light. Such films are of interest for use in a variety of photonic applications including display components, narrow band optical filters, low-threshold mirrorless lasing, sensors, and architectural, decorative, and security coatings. However, nonuniformities in the initial CNC dispersions and microstructural changes during drying typically result in uniform selective reflection only being achieved over length scales on the order of tens of microns. In this research, uniform photonic properties were achieved over orders of magnitude greater length scales by understanding the effects of initial concentration, orbital shear, surface anchoring, and drying conditions on films' microstructure and photonic properties. In addition, biomimetic films were produced which exhibited a double-peak spectra similar to that exhibited by the chiral nematic photonic structure in Lomaptera beetles.

In the context of valorization of lignin produced from the pulp and paper industries, biodegradable UV-protection films were prepared using lignin and cellulose nanocrystals (CNCs). Initially, CNC films were optimized for improving their transparency by studying the effect of various sodium hydroxide (NaOH) concentrations. Maximum (%) transmittance of CNC film was obtained for NaOH addition between 3 and 4 wt %. The optimized CNC suspensions were used for incorporating alkaline lignin (AL) and softwood kraft lignin (SKL) in various concentrations (1–10 wt %). Morphological characterization showed homogeneity of the lignin distribution in CNC/lignin films. Complete UV blocking was achieved at 10 wt % lignin (AL or SKL) in CNC films. Cross-polarized optical microscopy and scanning electron microscopic images of films showed some degrees of global alignment of CNC rods upon addition of NaOH, which remained unaffected by lignin addition. Lignin modification through acetylation reduced the lignin color and improved visible light transmission of films without significantly affecting the UV-absorption properties. Presence of lignin also enhanced the thermal and contact angle stability of the films. This work shows for the first time that CNC aqueous suspensions with and without containing lignin could be tuned through the addition of NaOH to produce transparent and homogenous films, providing a simple and green approach in engineering CNC/lignin UV-protection films.

Cellulose nanocrystals (CNC) have been studied as nanostructured building blocks for functional materials and function as a model nanomaterial mesogen for cholesteric (chiral nematic) liquid crystalline phases. In this study, both rheology and small angle neutron scattering (RheoSANS) were used to measure changes in flow-oriented order parameter and viscosity as a function of shear rate for isotropic, biphasic, liquid crystalline, and gel dispersions of CNC in deuterium oxide (DO). In contrast to plots of viscosity versus shear rate, the order parameter trends showed three distinct rheological regions over a range of concentrations. This finding is significant because the existence of three rheological regions as a function of shear rate is a long-standing signature of liquid crystalline phases composed of rod-like polymers, but observing this trend has been elusive for high-concentration dispersions of anisotropic nanomaterials. The results of this work are valuable for guiding the development of processing methodologies for producing ordered materials from CNC dispersions and the broader class of chiral nanomaterial mesogens.

Microelectromechanical systems (MEMS) have become a ubiquitous part of a multitude of industries including transportation, communication, medical, and consumer products. The majority of commercial MEMS devices are produced from silicon using energy-intensive and harsh chemical processing. We report that actuatable standard MEMS devices such as cantilever beam arrays, doubly clamped beams, residual strain testers, and mechanical strength testers can be produced via low-temperature fabrication of shear-aligned cellulose nanocrystal (CNC) films. The devices had feature sizes as small as 6 μm and anisotropic mechanical properties. For 4 μm thick doubly clamped beams with the CNC aligned parallel to the devices' long axes, the Young's moduli averaged 51 GPa and the fracture strength averaged 1.1 GPa. These mechanical properties are within one-third of typical values for polysilicon devices. This new paradigm of producing MEMS devices from CNC extracted from waste biomass provides the simplicity and tunability of fluid-phase processing while enabling anisotropic mechanical properties on the order of those obtained in standard silicon MEMS.

A Landau-de Gennes formulation was implemented in dynamic finite element simulations to compare with postshear relaxation experiments that were conducted on cholesteric cellulose nanocrystal (CNC) dispersions. Our study focused on the microstructural reassembly of CNCs in lyotropic dispersions as parameters such as chiral strength and gap confinement were varied. Our simulation results show that homeotropic and/or more complicated three-dimensional helical configurations are possible, depending on the choice of these parameters. We also observed how dynamic banding patterns develop into the hierarchical microstructures that are characterized by an equilibrium pitch length in both the experiments and simulations. This work has immediate relevance for cellulose nanocrystal dispersion processing and provides new insight into fluid phase ordering for tailorable optical properties.