Tuning the Optical and Thermal Properties of Both Iridescent and Colorless Cellulose Nanocrystal Films

The properties of iridescent and colorless cellulose nanocrystal (CNC) films can be modified through external stimuli. Here, the optical and thermal properties of CNC films were tuned by treating the aqueous suspension prior to casting. Three rapid and scalable methods (ultrasound treatment, dilution, and ion exchange) were selected, and the energy input, concentration, and alkali/alkaline-earth hydroxide were varied over a wide extent. The simultaneous change of the parameters enabled the synthesis of 360 CNC films with different properties, unlocking unprecedented photonic and thermal control spanning a broad range. The library of films showed systematic variations of nearly 50% of the range in film transparency, structural color peak wavelengths spanning two-thirds of the visible spectrum, and optimization of the thermal stability by more than 160 °C. A multiple linear regression of the effects of the three stimuli allows the prediction and choice of desired optical and thermal characteristics.