On the potential of zero-angle depolarized dynamic light scattering for rapid determination of solvent-dispersed cellulose nanocrystals

As the use of cellulose nanocrystals has grown, so has the need to characterize their sizes and the degree to which they are dispersed. Quick and reliable assessment of an individual batch would improve quality control, of great interest to producers, vendors, and users. While current techniques such as transmission electron microscopy, scanning probe microscopy, and asymmetric field flow fractionation enjoy high particle resolution, they are expensive and slow. This report concerns the potential of zero-angle depolarized dynamic light scattering as a low-cost, rapid, and straightforward method for cellulose nanocrystal length measurements. The technique proves more effective than traditional dynamic light scattering when it comes to differentiating between two separate cellulose nanocrystal samples in the important case where the difference resides not so much in the particle dimensions as in the state of dispersion. This much is evident from the raw data—i.e., without assumptions. When reasonable assumptions about the shape, hydrodynamics and optical nature of the nanocrystals are applied, zero-angle depolarized dynamic light scattering can reproducibly provide qualitative length distributions for billions of particles simultaneously. Pushing ahead to semiquantitative analysis remains a challenge, and full characterization of length, width and shape distributions still lies in the realm of particle-imaging forms of microscopy.