Cellulose photonic pigments

Abstract

When pursuing sustainable approaches to fabricate photonic structures, nature can be used as a source of inspiration for both the nanoarchitecture and the constituent materials. Although several biomaterials have been promised as suitable candidates for photonic materials and pigments, their fabrication processes have been limited to the small to medium-scale production of films. Here, by employing a substrate-free process, structurally coloured microparticles are produced via the confined self-assembly of a cholesteric cellulose nanocrystal (CNC) suspension within emulsified microdroplets. Upon drying, the droplets undergo multiple buckling events, which allow for greater contraction of the nanostructure than predicted for a spherical geometry. This buckling, combined with a solvent or thermal post-treatment, enables the production of dispersions of vibrant red, green, and blue cellulose photonic pigments. The hierarchical structure of these pigments enables the deposition of coatings with angular independent colour, offering a consistent visual appearance across a wide range of viewing angles.

The sustainable materials roadmap

“…A large part of the rock formation is either the product of organic matter, a massive accumulation of dead matter, compacted over thousands of years by colossal forces or it has been greatly influenced by living organisms at a planetary scale. We want to believe that human's building actions are the most recent factor in steering rock evolution 41 . This allegory would put us in a more appropriate position regarding our extractivist behaviour, and ultimately in the manner we produce architecture.…”

“…While CNC pigments can be prepared by dicing films into a dispersible glitter [38], a more disruptive strategy is to produce CNC pigments directly through the confinement of the self-assembly process within discrete micron-scale water droplets [40]. Upon drying, each microdroplet would produce a single, structurally coloured CNC microparticle [41]. The advantage of this approach is that it can readily build upon existing industrial emulsion technologies (e.g.…”

Deconvoluting the Optical Response of Biocompatible Photonic Pigments

“…Furthermore, given the drive within the colorant industry to transition away from PET‐based polymer glitters and the use of unrenewable minerals (e.g. mica) in effect pigments, such biocompatible photonic BBCP microparticles expand the range of available approaches to sustainable photonic pigments beyond existing strategies based on colloidal self‐assembly [36, 37] …”

Kinetic arrest during the drying of cellulose nanocrystal films from aqueous suspensions analogous to the freezing of thermal motions

“…As high-value-added functional nanostructured materials, cellulose nanocrystals (CNCs) provide various unique material functions that have prompted us to employ them in a wide range of applications [13][14][15][16][17] . One of the most recent advances in optoelectronic applications using CNCs is cellulose pigments 18 , which have even been used to produce films of CNCs with large-scale ordering 19 . In further detail, self-assembled CNCs were first confined within emulsified microdroplets.…”