Hydrodynamic and optical characteristics of hydrosols of cellulose nanocrystals

Dynamic light scattering, viscometry, sedimentation, densitometry, refractometry, flow birefringence, and electrically induced dichroism were used in the studies of hydrosols of cellulose nanocrystals (CNC). Visualization of CNC particles and primary evaluation of their size were performed with the use of atomic force microscopy (AFM). The set of data on hydrodynamic and optical properties of the studied particles in aqueous medium was obtained. The particle size distribution demonstrates wide polydispersity. The values of translational and rotational friction coefficients, intrinsic viscosity, and quantitative data on sedimentation, density, and flow birefringence of CNC sols were obtained. Contributions of particles of various sizes into the phenomena caused by translational and rotational friction of CNC samples were analyzed in detail. It was established that hydrodynamic and optical properties of CNC hydrosols can be described using the model of ellipsoid of revolution with a shape asymmetry parameter (p) equal to 20. According to the data of hydrodynamic studies, the main CNC fraction consists of particles with a length of the order of 300–400 nm. It was demonstrated that optical characteristics of CNC hydrosols are determined by the contribution of large particles (with the characteristic longitudinal size of 1500 nm and above) into flow birefringence and electric dichroism. It was found that the AFM data alone cannot provide insight into morphology of CNC hydrosols.