(224f) 3D Printing of Chiral Liquid Crystal Elastomers Using Cellulose Nanocrystals

Cellulose nanocrystals, CNCs in polar solvents (such as water and DMSO) can self-assemble into a chiral nematic structure at low concentrations (below 10 wt.%). Therefore, the pure CNC suspensions do not have sufficient viscoelasticity required for 3D-printing applications. To enhance the viscoelasticity of the pure CNC suspensions in DMSO, we have incorporated photo-curable monomers (such as 2-Hydroxyethyl methacrylate (HEMA)), which improve the filament mechanical properties when exposed to UV light. We have studied the effect of the CNC:HEMA ratio in DMSO on the chiral nematic self-assembly of CNCs before and after 3D-printing. Our polarized optical microscopy results showed that the CNC:HEMA (wt%) ratios of 1:6 and 1:8 exhibit cholesteric structures at stationary conditions. We have performed flow-induced birefringence measurements to explore the effect of monomer addition on the flow-induced alignment. We have further studied the relaxation dynamics of the chiral structures after stopping the flow. Our results showed that, over the course of 3D printing, the shear flow in the 3D-printer nozzle can unwind the chiral nematic structure and align the CNC particles along the flow axis. The chiral nematic structure was, however, fully recovered a few minutes after stopping the flow. After printing, the chiral nematic ink (CNC+monomer) was exposed to UV light to complete the photopolymerization. The presence of chiral structures in the printed part was confirmed using Polarized Optical Microscopy and Scanning Electron Microscopy. Moreover, they reveal the perpendicular alignment of the chiral nematic structure with respect to the printing direction. These new findings can pay the way to develop new ink formulations for 3D printing of architectures with internal chirality for advanced mechanical and smart photonic applications.