Flexible cellulose nanocrystal-based bionanocomposite film as a smart photonic material responsive to humidity

A flexible bionanocomposite film with a visible structural color was developed by co-assembling cellulose nanocrystals with glycerol, glucose, and poly(vinyl alcohol), and its application as a photonic humidity-responsive material was investigated. This chiral nematic film exhibited an indigo, cyan, olive green, orange, pink, and transparent color when exposed to relative humidity of 33%, 75%, 85%, 89%, 96%, and 100%, respectively. The color change was caused by reversible change in chiral nematic pitch due to hydration and dehydration. The nanocomposite displayed a stable structural color after alternatively conditioned at 33% and 100% relative humidity for ten cycles. Notably, material cost for a piece of such a smart film with an area of 28 cm2 is less than $0.1 USD. This flexible, uniform bionanocomposite film has great potential to be used as a smart photonic material responsive to humidity.