Chiral Self-Assembly of Cellulose Nanocrystals is Driven by Crystallite Bundles

TL;DR

This study uncovers how chiral cellulose nanocrystal bundles influence the self-assembly process, revealing their role as colloidal chiral dopants that transfer molecular chirality to large-scale structures.

Contribution

It demonstrates that cellulose nanocrystal bundles act as chiral dopants, linking molecular chirality to mesoscopic self-assembled structures in a hierarchical manner.

Findings

Inverse relationship between cholesteric pitch and bundle abundance

Bundles act as colloidal chiral dopants

Hierarchical transfer of chirality from molecules to structures

Abstract

The transfer of chirality across length-scales is an intriguing and universal natural phenomenon. However, connecting the properties of individual building blocks to the emergent features of their resulting large-scale structure remains a challenge. In this work, we investigate the origins of mesophase chirality in cellulose nanocrystal suspensions, whose self-assembly into chiral photonic films has attracted significant interest. By correlating the ensemble behaviour in suspensions and films with a quantitative morphological analysis of the individual nanoparticles, we reveal an inverse relationship between the cholesteric pitch and the abundance of laterally-bound composite particles. These bundles thus act as colloidal chiral dopants, analogous to those used in molecular liquid crystals, providing the missing link in the hierarchical transfer of chirality from the molecular to the colloidal scale.