Xanthan-Induced Gelation in Cellulose Nanocrystal Suspensions: Tuning of the Self-Assembly and Optical Purity

Cellulose nanocrystals (CNCs) are anisotropic nanoparticles that can undergo chiral self-assembly in aqueous suspension to produce vibrant structurally colored films with a helicoidal nanostructure resembling the cholesteric structures found in natural systems. Above a critical concentration, CNC suspensions form a cholesteric liquid crystal phase and small clusters of order called tactoids, with a periodicity (pitch) determined by the colloidal interactions between the CNCs, and further parameters affecting the dynamics of the evaporation. Upon further drying, the CNCs undergo kinetic arrest, which allows their helicoidal ordering to be preserved in the solid state. The color and the angular dependence in these films can be tuned using numerous experimental parameters. Such films can be used to produce optically active components or processed further. In this study, we explore two differently processed CNC colloidal suspensions and their interactions with a food-grade gelating agent with the aim to explore the onset of the gelation point. The Xanthan gum used here is produced by the fermentation of simple sugars by the bacteria <i>Xanthomas campestris</i>. While the presence of the complex polysaccharide gum brings flexibility to the CNC films, the films also demonstrate remarkable color uniformity and loss of iridescence due to the entrapment of the CNC tactoids into encapsulated structures to combine a surface texture and scattering of visible light within the co-assembled structure. In this talk, I will explain how in the evaporation stage Xanthan advances the onset of gelation and provides colloidal stability, thus restricting the expected phase separation into smaller-scale events as compared to pure CNC films. This work sheds new light on the gelation mechanisms in hybrid CNC systems, their interaction with an additive of alike chemistry, and self-assembly in a phase-stabilized environment.