Critical discussion of light scattering and microscopy techniques for CNC particle sizing

Abstract

The determination of particle length and aspect ratio of acicular cellulose nanocrystals (CNCs) becomes crucial when CNCs are used as a catalyst or as a reinforcement additive or when their size is used as a quality control parameter for production. We measured particle dimensions and particle size distribution of CNCs using several experimental techniques based on electron and optical microscopy as well as static and dynamic light scattering. Electron microscopy can easily reveal the real dimensions (i.e. length and cross-section) of non-symmetrical particles like CNCs while the light-scattering derived techniques cannot. With the latter, it is however possible to approximate the real dimensions using the appropriate theory. The different aspects of light scattering techniques and types of data that can be obtained are presented and detailed. For each technique used, measurements done with CNCs are compared to those obtained with spherical standard latex particles. The accuracy of the final data was also related to the time necessary to obtain it. This "accuracy over time" ratio is of importance when specific applications such as on-line quality control are targeted.