The fabrication of structurally colored films that exploits self-assembly methods and abundant biosourced materials allows for the development of simple and scalable materials with a broad range of properties and applications. The use of cellulose nanocrystals (CNCs), chiral colloidal nanorods extracted by acid hydrolysis of cellulose, has demonstrated the ability to produce such films upon casting in a dish. Upon solvent evaporation, CNCs spontaneously arrange into a cholesteric order that is retained in the resulting solid film, with an associated submicron periodicity that enables the reflection of specific wavelengths in the visible range. While these films were discovered over two decades ago, they have recently regained interest for their ability to produce multifunctional optical materials, usually by exploiting their ability to co-assemble with additional guests species such as small molecules, polymers, nanoparticles, surfactants or sol-gel precursors. However, the addition of additional species can easily disturb or hinder their self-assembly and the conditions of successful co-assembly remain unclear.<br/><br/>In this talk, I will discuss the conditions of successful co-assembly conditions required between CNCs and regenerated silk fibroin (SF), a globular protein extracted from the <i>B. Mori</i> silkworm. SF is a multifunctional protein that is biocompatible, food-safe and even edible, and that also present excellent transparency, mechanical and oxygen barrier properties. The pH and the SF:CNC ratio adjustments appear as the main factors controlling the microstructure and the optical properties of the resulting films: homogeneous structurally colored films can be produced at pH &gt; 4, which coincides with the isoelectric point (pI) of the main hydrophilic motifs on the SF heavy chain. The resulting films present improved adhesion properties. This opens possibilities in bio-friendly, colorful, comestible pigments or protective food packaging.

Co-assembly conditions of cellulose nanocrystals and silk fibroin into photonic cholesteric films

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.