Controlling the Photonic Properties of Cholesteric Cellulose Nanocrystal Films with Magnets

The self-assembly of cellulose nanocrystals is a powerful method for the fabrication of biosourced photonic films with a chiral optical response. While various techniques have been exploited to tune the optical properties of such systems, the presence of external fields has yet to be reported to significantly modify their optical properties. In this work, by using small commercial magnets (≈ 0.5-1.2 T) the orientation of the cholesteric domains is enabled to tune in suspension as they assemble into films. A detailed analysis of these films shows an unprecedented control of their angular response. This simple and yet powerful technique unlocks new possibilities in designing the visual appearance of such iridescent films, ranging from metallic to pixelated or matt textures, paving the way for the development of truly sustainable photonic pigments in coatings, cosmetics, and security labeling.This work was supported by a BBSRC David Phillips fellowship [BB/K014617/1], the EPSRC [1525292] and the European Research Council [ERC-2014-STG H2020 639088]

Dynamically Controlled Iridescence of Cholesteric Cellulose Nanocrystal Suspensions Using Electric Fields

Cellulose nanocrystal suspensions in apolar solvent spontaneously form iridescent liquid crystalline phases but the control of their macroscopic order is usually poor. The use of electric fields can provide control on the cholesteric orientation and its periodicity, allowing macroscopic sample homogeneity and dynamical tuning of their iridescent hues, and is demonstrated here.The authors acknowledge funding by the French National Research Agency under grant agreement ANR-08-NANO-P235-36 and B.F-P. acknowledges the Travel Grant COST-STSM-FP1205-30247