Tailoring the Morphology of Cellulose Nanocrystals via Controlled Aggregation

Abstract: Cellulose nanocrystals (CNCs) are bioderived nanoparticles that can be isolated from various sources of natural cellulose via acid hydrolysis. However, the link between particle morphological characteristics and their ensemble behavior is poorly understood, partly because of the difficulties in controlling the CNC morphology during their extraction process. In this work, the impacts of common post-hydrolysis treatments on the CNC morphology are investigated. The results indicate that the centrifugation step commonly applied during CNC purification favors the formation of composite particles made of aligned crystallites, referred to as 'bundles'. Scanning nanobeam electron diffraction reveals that such bundles are associated preferentially along their hydrophobic faces. This is in stark contrast to the formation of misaligned composite particles that can be achieved with ionic treatments, where an uncontrolled aggregation occurs. The functional relevance of these morphological differences is demonstrated by their effect on the cholesteric self-organization of CNCs, with bundles found to exhibit a greater chiral enhancement, whereas the misaligned composite particles found to promote gelation. This study reveals the importance of the often-disregarded purification steps on the final morphology of CNCs and their resulting ensemble properties, thereby unlocking new routes for tailoring this promising material towards a variety of applications.