Cellulose nanocrystals suspensions: Liquid crystal anisotropy, rheology and films iridescence

[Display omitted] •Aqueous suspensions of cellulose nanocrystals form chiral nematic liquid crystals.•Effect of crystals morphology, concentration and surface chemistry are reviewed.•Suspensions rheology is ruled by the above variables and by media ionic strength.•Importance of the drying process on the films characteristics is discussed.•Iridescence and optical responses are aimed to be controlled in applications. The properties of aqueous suspensions of cellulose nanocrystals (CNC) and their casted films are revised. The bio-nanoparticles are briefly introduced, including modifications of the crystals and the suspending media. The formation of CNC-derived liquid crystals (LC) and their resulting rheological behavior are presented. The effects of different variables are addressed: CNC aspect ratio, surface chemistry, concentration, time required for the appearance of an anisotropic phase and addition of other components to the suspension media. The changes on the structure induced by alignment, and by conditions of the drying process are also reported. The optical properties of the films are considered, and the effect of the above variables on the final transparency, iridescence and overall optical response of these bio-inspired photonic materials. Control of the reviewed variables is needed to achieve reliable materials in applications such as sensors, smart inks and papers, transparent flexible supports for electronics, decorative coatings and films.