Cellulose nanofibrils and nanocrystals in confined flow: Single-particle dynamics to collective alignment revealed through scanning small-angle x-ray scattering and numerical simulations

Abstract

Nanostructured materials made through flow-assisted assembly of proteinaceous or polymeric nanosized fibrillar building blocks are promising contenders for a family of new high-performance biocompatible materials in a wide variety of applications. Optimization of these processes relies on improving our knowledge of the physical mechanisms from nano-to macroscale and especially understanding the alignment of elongated nanoparticles in flows. Here, we study the full projected orientation distributions of cellulose nanocrystals (CNC) and nanofibrils (CNF) in confined flow using scanning microbeam SAXS. For CNC, we further compare with a simulated system of dilute Brownian ellipsoids, which agrees well at dilute concentrations. However, increasing CNC concentration to a semi-dilute regime results in locally arranged domains called tactoids, which aid in aligning the CNC at low shear rates, but limit alignment at higher rates. Similarly, shear alignment of CNF at semi-dilute conditions is also limited owing to probable bundle/flock formation of the highly entangled nanofibrils. This work provides a first quantitative comparison of full projected orientation distributions of elongated nanoparticles in confined flow and provides an important stepping stone towards predicting and controlling processes to create nanostructured materials on an industrial scale.

Shear-free mixing to achieve accurate temporospatial nanoscale kinetics through scanning-SAXS: ion-induced phase transition of dispersed cellulose nanocrystals

“…The samples used in this study was commercial CNCs (produced through acid hydrolysis) made from bleached wood pulp provided by the Process Development Center in University of Maine. The same material was used and characterized in the work by Rosén et al 11 The TEM image of Fig. 2 Schematic illustration showing how flow rates influence the flow and time scales.…”

“…8 In addition, the high brilliance and tunability of synchrotron X-rays allowed the sample environments to be tailored for new in situ studies, including e.g. magnetic fields, 9,10 flow deformations 11,12 and mixing. 13 The development of microfocusing X-ray beam capability further enabled the ability of spatial mapping to investigate the structural variations in samples with micrometer-resolution using the scanning-SAXS technique, demonstrated both for solid samples in 2D [14][15][16] and 3D, 17,18 as well as in flows.…”

“…13 The development of microfocusing X-ray beam capability further enabled the ability of spatial mapping to investigate the structural variations in samples with micrometer-resolution using the scanning-SAXS technique, demonstrated both for solid samples in 2D [14][15][16] and 3D, 17,18 as well as in flows. 11,19 The combination of SAXS with various mixing experiments has already been seen as a powerful tool to obtain timeresolved transitions including kinetics of RNA or protein folding. [20][21][22] Resolving the structural kinetics in traditional mixing experiments using stopped-flow techniques 23 is inherently problematic because the influence of the radiation itself needs to be corrected (the system often requires to be irradiated for a sufficient period of time to ensure the desired signal-to-noise ratio).…”

Self-organization of nanoparticles and molecules in periodic Liesegang-type structures

“…5B). More specifically, we computed the 2D orientation distribution function (ODF), f(), which reflects the probability of the scatterers to be aligned in a particular direction (40,41) and is calculated as 5C shows the ODF for a typical examined spot of the TA/CNC film. We then fitted the ODF profiles (Fig.…”

“…4. Furthermore, to evaluate the orientation of anisotropic species in the film, the orientation order parameter, S, in the plane of the film was computed (40,41), with S = 1 for the perfect alignment and S = 0 for a randomly oriented system (Fig. 5E).…”