Recent Advances and Opportunities for Cellulose Nanocrystal-Based Liquid Crystalline Polymer Hybrids and Composite Materials

Cellulose nanocrystals (CNCs) areone-dimensional, rod-like, anisotropic,renewable, sustainable, and degradable polysaccharide-based materialswith a high aspect ratio and tunable surface chemistry. The intriguingability of CNCs to self-assemble into a lyotropic chiral nematic orcholesteric liquid crystal phase with a helical arrangement that exhibitsbirefringence, iridescence, and pitch-dependent 1D photonic propertieshas attracted significant research interests. However, there are severalroadblocks in the application of CNCs as sustainable and degradableliquid crystal (LC) materials. These include (i) problems with aggregationof CNCs that prevent solubility in different solvents, (ii) difficultiesin processing, aligning, and spatial and temporal control of lyotropicgels and dried films of CNCs, and (iii) poor mechanical and viscoelasticproperties of these gels and films. This Perspective describes thesynthetic methods used to functionalize CNCs with LC pendants or liquidcrystalline polymers (LCPs) by chemical conjugation or physical self-assembly.These CNC hybrid materials showed improved solubility in a varietyof solvents. The interplay between the liquid crystalline CNCs andliquid crystalline LCs or LCPs during self-assembly can be tailoredby selecting LCs or LCPs of a diverging orientation order. The finalself-assembled hierarchical structure with or without a field-directedassembly can be used to fabricate stimuli-responsive CNC hybrid materials.Furthermore, kinetic and thermodynamic control to align LC domainsand prepare materials with long-range order are also discussed. Finally, spatial-temporal control, viscoelastic properties, and degradationof the CNC hybrid materials and their applications are also reported.