Parameters Affecting the Chiral Nematic Phase of Nanocrystalline Cellulose Films

Nanocrystalline cellulose (NCC) is extracted from woody biomass using acid hydrolysis. It has unique strength and distinctive optical/conductive/magnetic properties. When a suspension of NCC is air-dried, it forms a film with unique characteristics (e.g., iridescence) linked to the formation of chiral nematic structure. In this contribution, the effects of ionic strength, temperature, suspension concentration, and exposure to magnetic field on the morphology of NCC are examined. The influence of these parameters on chiral nematic phase is investigated at a macroscopic level using circular dichroism and polarized microscopy. It is demonstrated that the addition of salt to NCC suspensions, NCC concentration, temperature, and the presence of a magnetic field all have an effect on the pitch of the chiral nematic structure. For example, drying of the NCC film in the presence of a 0.2 T external magnetic field increases the pitch, in a manner dependent on drying time. The implication of these results for the structure and properties of NCC is discussed.