Direct Ink Writing of 3D Chiral Soft Photonic Crystals

Abstract

Blue phase liquid crystals (BPLCs) are regarded as self-organized 3D chiral soft photonic crystals with iridescent, tunable, and circularly polarized structural colors. However, arbitrary patterning of BPLCs with satisfactory microscopic self-assembly remains challenging. Here, the direct ink writing of 3D chiral soft photonic crystals using BPLC precursor inks is reported. The dynamic evolution of a BPLC ink droplet cooling from an isotropic state to a blue phase state is studied to prepare mono-domain BPLCs with high reflectivity. The diverse macroscopic design of BPLC patterns can be obtained by printing the BPLC inks on different substrates, and controlled self-assembly enables high color brightness, circularly polarized reflection, and sufficient thermal stability after photo-polymerization. Interestingly, the angle-dependent optical properties of the printed lines and faces are found to be different due to the 3D photonic nanostructures of BPLCs. The research disclosed here provides unprecedented controllability in the fabrication of patterned 3D soft photonic crystals and extends their applications in displays, optical devices, 3D optics, and photonics.