Suspension viscosities and shape parameter of cellulose nanocrystals (CNC)

The successful application of nanoscale materials requires an accurate description of the shape and size of the nanomaterial. Cellulose nanocrystals (CNC) are a plant-derived nanomaterial that is currently being investigated for a variety of applications. We have developed here a method to determine the shape parameter (length/diameter) of rod-like CNC particles using bulk viscosity measurements of CNC solutions. The cellulose nanocrystals were prepared by concentrated sulfuric acid hydrolysis of wood pulp. CNC particles in aqueous solutions carry negative electrical charges due to the sulfate surface groups and showed electroviscous effects. The viscosities of cellulose nanocrystals suspensions were measured at various NaCl electrolyte concentrations and intrinsic viscosities were calculated. The extrapolation of intrinsic viscosity to 1 nm Debye length was used to calculate intrinsic viscosity of hard rods without electroviscous effects. The corresponding shape factor calculated from Simha's equation was 41. Atomic force microscopy (AFM) was used to measure the shape parameter of individual CNC particles. Limited number of measurements yielded an average value of 30. Intrinsic viscosity measurements would be a reliable and relatively simple method to calculate the shape factor of rod-shaped cellulose nanocrystals after electroviscous effects are corrected.

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► Electrical double layer contributes to the viscosity of the CNC suspensions.
► NaCl electrolyte concentration of higher than 10 mM causes coagulation.
► Intrinsic viscosity is a simple method to calculate the shape factor of CNC rods once the electroviscous effects are factored in.
► The shape factor (L/d) of 41 was calculated from Simha's equation after electroviscous effects were taken into account.