Cellulose Photonic Pigments

TL;DR

This paper presents a sustainable, substrate-free method to produce vibrant, angle-independent cellulose-based photonic pigments through confined self-assembly and buckling of cholesteric cellulose nanocrystals in microdroplets.

Contribution

It introduces a novel, scalable process for creating structurally coloured cellulose microparticles with angle-independent optical properties.

Findings

Produced vibrant red, green, and blue cellulose photonic pigments.

Achieved coatings with consistent colour across various viewing angles.

Demonstrated a scalable, substrate-free fabrication process.

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.