Lyotropic liquid crystal self-assembly of H₂O₂-hydrolyzed chitin nanocrystals

H₂O₂ hydrolysis of mechanically-defibrillated chitin nanofibrils was explored as a green way of fabricating rod-like chitin nanocrystals (H₂O₂-hydrolyzed CHNs) that have an average length of 350 nm and width of 40 nm. We investigated the structure and morphology of CHNs as well as the rheology and lyotropic self-assembly behavior of its colloidal dispersions. The results show that although H₂O₂-hydrolyzed CHNs maintained the crystalline structure of α-chitin, surface charge of the nanorods was switched from positive to negative. As a consequence, the colloidal nanocrystals were well-dispersed in neutral or alkaline aqueous media, and behaved as a lyotropic liquid crystal between two critical concentrations. It is interesting that lyotropic liquid crystal transition was a spontaneously self-assembly from well-aligned nanofibers, to nanobelts, and to multi-layered lamellae. At high critical concentration, H₂O₂-hydrolyzed CHN colloids exhibited a sol-gel transition, which was discovered to be highly dependent on the storage time, concentration, temperature, and surface charge density. It is also suggested that nematic mesophases rather than gel could be effectively maintained by improving the surface charge density or lowering the aging temperature and colloidal concentration of CHNs.