Revealing and Quantifying the Three-Dimensional Nano- and Microscale Structures in Self-Assembled Cellulose Microfibrils in Dispersions

Cellulose microfibrils (CMFs) are an important nanoscale building block in many novel biobased functional materials. The spatial nano- and microscale organization of the CMFs is a crucial factor for defining the properties of these materials. Here, we report for the first time a direct three-dimensional (3D) real-space analysis of individual CMFs and their networks formed after ultrahigh-shear-induced transient deagglomeration and self-assembly in a solvent. Using point-scanning confocal microscopy combined with tracking the centerlines of the fibrils and their junctions by a stretching open active contours method, we reveal that dispersions of the native CMFs assemble into highly heterogeneous networks of individual fibrils and bundles. The average network mesh size decreases with increasing CMF volume fraction. The cross-sectional width and the average length between the twists in the ribbon-shaped CMFs are directly determined and compared well with that of fibrils in the dried state. Finally, the generality of the fluorescent labeling and imaging approach on other CMF sources is illustrated. The unique ability to quantify in situ the multiscale structure in CMF dispersions provides a powerful tool for the correlation of process-structure-property relationship in cellulose-containing composites and dispersions.