Iridescent, Flexible, Hydrophobic Polymer Composite Films from Self-Assembled Cellulose Nanocrystals.

Cellulose nanocrystals (CNCs) are known for their ability to form iridescent films with structural color via solidification of a chiral nematic liquid crystalline phase. However, the inherent brittleness and hydrophilicity of CNCs make them fragile and susceptible to moisture, limiting their versatility. To address these issues, an innovative strategy has been developed to overcome the incompatibility between hydrophilic CNCs and hydrophobic polycaprolactone (PCL), and a series of hydrophobic iridescent CNC-PCL composite films has been prepared. The soft PCL was homogenously entrapped in the chiral nematic CNC matrix through film swelling, solvent exchange, and ambient drying, while the photonic structure of the assembled CNCs was well retained. These composite materials are iridescent, flexible, and hydrophobic, making them promising candidates for waterproof photonic coatings. Furthermore, their structural color, flexibility, and hydrophobicity were readily adjusted by tuning the proportion of PCL in the CNC matrix. It is expected that this new strategy will open the door for future researchers to develop water-resistant and flexible photonic materials by blending photonic crystals and hydrophobic polymers, as well as expanding their application scenarios.