Optically tunable chiral nematic mesoporous cellulose films†
Demand for sustainable functional materials has never been larger. The introduction of functionality into pure cellulose might be one step forward in this field as it is one of the most abundant natural biopolymers. In this paper, we demonstrate a straightforward and scalable way to produce iridescent, mesoporous cellulose membranes with tunable colors and porosity. Concomitant assembly of cellulose nanocrystals (CNCs) and condensation of silica precursors results in CNC–silica composites with chiral nematic structures and tunable optical properties. Removal of the stabilizing silica matrix by alkaline or acid treatment gives access to novel chiral nematic mesoporous cellulose (CNMC) films. Importantly, the optical properties and the mesoporosity can be controlled by either varying the silica-to-CNC ratio, or by varying the substrate used during the evaporation-induced self-assembly process. In order to introduce additional functionality, CNMC has been used to stabilize gold nanoparticles with three different concentrations by wet impregnation. These materials are stable in water and can potentially function in sensors, tissue engineering or functional membranes.