Multi-functional coating of polymeric spherulites for chiral photonic cellulose nanocrystal films

Cellulose Nanocrystal (CNC) films are from emerging nanoparticles recently known for photonic properties. The CNC films show nonuniform photonic domains resulting from structural irregularities in their typical self-assembled arrangements. This paper presents a drop-casting approach from Polyamide 6 to form a coating layer on the CNC films. This coating approach led to polycrystalline growth patterns known as spherulites on the CNC film. For the resulting coated CNC film, the spherulites yielded a unique set of enhanced physical properties including optical, mechanical and thermal as well as a new morphological appearance from their micro-scale average spherical shape; the ordering effect of their local radial symmetry and orientation positively influenced the effects of structural irregularities of the typical CNC films. Under polarized light, the optical transmission bands of the CNC film were perceived through radial symmetry of banded spherulites which were responsible for the formation of circular extinction patterns for the coated CNC film. The intermolecular interactions and interlamellar entanglement of spherulites provided enhanced flexibility and tensile strength for the coated CNC film. This protecting design allows for the future development of a variety of portable functional assemblies requiring enhanced performance in optical, mechanical and thermal properties of CNC films.