Homeotropic Concentric Helix Orientations in Chiral Nematic Cellulose Nanocrystal Films by Local Magnetic Fields

Many fascinating device applications of chiral nematic materials are determined by their helical axis orientations. Cellulose nanocrystals (CNCs) self-assemble producing left-handed chiral nematic films with predominant planar textures. While varied techniques have been exploited to tune the helical axis orientations, it remains challenging to produce concentrically aligned chiral nematic state. Herein, the authors report novel findings that left-handed chiral nematic CNC films formed with homeotropic concentric helix orientations in the planar textures can be realized by local radial magnetic field-directed self-assembly of CNCs. These chiral nematic CNC films display left-handed circular polarization patterns and transform spontaneous luminescence to right-handed circularly polarized luminescence on both film plane and lateral surfaces owing to the underlying photonic bandgaps. These plane-lateral chiroptical properties can be tuned simultaneously from the visible to the near-infrared spectral regime. Their work presents a step towards the development of self-organized chiroptical materials encoded with complex polarization features for photonic applications.