Spontaneous Co-Assembly of Cellulose Nanocrystals and TiO₂ Nanorods Followed by Calcination to Form Cholesteric Inorganic Nanostructures

Abstract

Chiral nanomaterials possess unique electronic, magnetic, and optical properties that are relevant to a wide range of applications including photocatalysis, chiral photonics, and biosensing. A simple, bottom-up method to create chiral, inorganic structures is introduced that involves the co-assembly of TiO2 nanorods with cellulose nanocrystals (CNCs) in water. To guide experimental efforts, a phase diagram was constructed to describe how phase behavior depends on the CNCs/TiO2/H2O composition. A lyotropic cholesteric mesophase was observed to extend over a wide composition range as high as 50 wt % TiO2 nanorods, far exceeding other examples of inorganic nanorods/CNCs co-assembly. Such a high loading enables the fabrication of inorganic, free-standing chiral films through removal of water and calcination. Distinct from the traditional templating method using CNCs, this new approach separates sol–gel synthesis from particle self-assembly using low-cost nanorods.

Aqueous Coassembly of Small TiO2 Nanorods with Cellulose Nanocrystals into Transparent, Uniaxially Aligned Inorganic Thin Films for Waveplates

“…Here, we focus on the use of CNCs to facilitate the alignment of small, low aspect ratio TiO 2 nanorods. A compositional phase diagram of colloids suspensions containing both TiO 2 nanorods and cellulose nanocrystals was previously published and guided our experimental effort …”

“…A compositional phase diagram of colloids suspensions containing both TiO 2 nanorods and cellulose nanocrystals was previously published and guided our experimental effort. 32 Lyotropic suspensions containing TMAH-stabilized TiO 2 and CNCs were shear-aligned via blade-coating using a customized apparatus (see Figure S1) operating under optimized conditions (blade speed of 2.3 cm/s and gap distance of 10 μm) to yield oriented composite films. When placed between cross polarizers, the dried films appear bright or dark if the blade-coat direction is oriented at 45°or 0°, respectively, to one of the polarizers (Figure 1c,d), indicating that the coating is birefringent with uniaxial orientation.…”

Tunable Construction of Chiral Nematic Cellulose Nanocrystals/ZnO Films for Ultra-Sensitive, Recyclable Sensing of Humidity and Ethanol

“…The research provides a new strategy for combining Chiral CNC materials with metal oxides to enable varying applications. Recently, the co-assembly behavior of high-loading TiO 2 nanorods with CNCs in suspension was researched through water removal and calcination, indicating an approach of universal application of ligand-stabilized inorganic nanorods [25].…”