Chiral Co-assembly of Titania Nanorods and Cellulose Nanocrystals*

Chiral inorganic nanomaterials are sought after in various fields owing to their unique optical, electric, magnetic properties and could impact various applications in optical materials, catalysis, chiral separation and biomedicine. Here, a novel and cost-effective bottom-up method for fabricating chiral mesomorphic ceramics was achieved via co-assembly between TiO₂ nanorods and cellulose nanocrystals (CNCs). The methods is general, and the colloidal stability offered by TiO₂ and CNC stabilized with tetramethylammonium hydroxide (TMAH) could likely be extended to other inorganic particles. A phase diagram showing the mesophase behavior of co-assembled TiO₂ nanorods and CNCs at various compositions was experimentally determined and provided guidance for film fabrication. Films were fabricated by both evaporation-induced self-assembly (EISA) and vacuum-assisted self-assembly (VASA).  A comparison of the two methods shows that EISA offers higher transparency, and therefore it was selected to prepare chiral mesomorphic ceramic films.  Composite films prepared by EISA were subject to thermal treatment to remove the CNCs, and the inorganic superstructure partially preserved the chirality templated by the CNCs.