(164ab) Effect of Temperature and Monomer Addition on Rheological Properties of Chiral Cellulose Nanocrystals Suspensions

When cellulose nanocrystals (CNCs) are dispersed in polar solvents (such as water and DMSO), they form chiral structures and exhibit flow behavior characteristic of lyotropic liquid crystals. Their viscosity curve versus shear rate depicts three characteristic regimes, each associated with a distinct structural arrangement; shear-thinning at low shear rates, where the chiral domains start to flow (regime I); a plateau viscosity profile at medium shear rates, where chiral domains are broken (regime II), and a shear-thinning regime at high shear rates, where individual particles start to align (regime III). The chirality is, however, achieved at low CNC concentration (below 10 wt%), leading to poor mechanical properties. Here we have studied the coupling of temperature and addition of 2-hydroxyethyl methacrylate (HEMA) monomer on the chiral nematic structure of dispersed CNC particles in DMSO. We measured the rheological properties of the mixtures at different temperatures and monomer contents. Polarized optical microscopy, POM was used to elucidate the formation of the chiral structures. Our POM results revealed that the addition of HEMA at room temperature up to the CNC:HEMA ratio of 1:6 wt.% does not interfere with the chiral nematic structure of the CNC particles in DMSO. The presence of chiral nematic structure was also confirmed by three characteristic viscosity regimes of lyotropic liquid crystals upon rheological measurements. Elevating the temperature to 65°C, the chiral structure was preserved up to CNC:HEMA ratio of 1:10 wt.%. These CNC-based inks can be used for the 3D-printing of architectures with the chiral nematic structure for photonics and advanced mechanical applications.