Biomimetic Colour Engineering From Nature to Applications

In a changing world, Nature must serve as a source of inspiration to develop more sustainable materials. For instance, plants' most brilliant and striking colours result from the helicoidal arrangement of cellulose nanofibrils. Interestingly, similar helicoidal architectures with analogous optical responses can be obtained in vitro by self-assembly of cellulose nanocrystals (CNCs) derived from biomass&lt;font size="1"&gt;.&lt;/font&gt;<br/>CNCs are rod-like colloids capable of arranging into a liquid crystalline phase above a critical concentration in suspension, which upon complete removal of the solvent, lead to photonic films. So far, this process has been explored and studied only on a relatively small scale, neglecting the limitations and challenges posed by the use of large-scale and continuous processes which are required in any industrial context.<br/>In this presentation, I will address these limitations by demonstrating how the self-assembly of CNCs can be controlled to produce meters-long films using a roll-to-roll (R2R) technique. Particularly, we demonstrated how the suspension properties, the casting parameters and drying conditions relate to the optical properties of the produced films.<br/>To validate the use of this technique and material for pigment preparation, we developed a protocol to prepare coloured microparticles from R2R-cast CNC films. The optical properties of the CNC microparticles were then assessed in various environments and finally benchmarked against other commercial effect pigments and glitter. The prepared microparticles are compatible with a wide range of formulations, making them ideal to replace controversial mineral pigments based on mica and titanium dioxide as well as non-biodegradable glitters.