Spatially and flow-sensitive alignment of cellulose nanocrystals during nanoscale confinement

Cellulose nanocrystals (CNCs) are highly shape-anisotropic nanoparticles that show great promise as sustainable nanoscale building blocks. The properties of CNC-based materials are highly dependent on the particle alignment, and flow is an attractive means to control this. However, fundamental understanding of how particle structure couples with flow and colloidal forces is lacking. We hypothesise that dynamic thin film confinement will induce a high level of particle alignment, leading to non-Newtonian drainage. Furthermore, thin film behaviour is expected to be controlled by long-range structural forces due to induced particle layering.

Dual-wave interferometry was used to investigate the dynamics of CNC fluids confined between a bubble and a solid surface. Bulk phase properties were analysed using small-angle neutron scattering and rheology.

Film behaviour is dominated by fluid flow (hydrodynamic force) for thick films, and this controls initial stages of film drainage. However, a transition occurs later in film drainage whereby long-range structural forces, from confined particle-particle interactions, sculpts thin film morphology. Bulk phase properties measured using rheology and small-angle neutron scattering provide complementary insight into lubrication dynamics, indicating that CNC anisotropy couples with flow and confinement conditions present within thin films, resulting in spatially-sensitive induced orientation. This study demonstrates the nuanced role of anisotropic features in confined flow and suggests opportunities for flow-based orientational control of sustainable nanomaterials.