Decoupling the effects of shear and extensional flows on the alignment of colloidal rods

Abstract

Cellulose nanocrystals (CNC) can be considered as model colloidal rods and have practical applications in the formation of soft materials with tailored anisotropy. Here, we employ two contrasting microfluidic devices to quantitatively elucidate the role of shearing and extensional flows on the alignment of a dilute CNC dispersion. Characterization of the flow field by micro-particle image velocimetry is coupled to flow-induced birefringence analysis to quantify the deformation rate--alignment relationship. The deformation rate required for CNC alignment is 4$\times$ smaller in extension than in shear. Alignment in extension is independent of the deformation rate magnitude, but is either 0${}^{\circ }$ or 90${}^{\circ }$ to the flow, depending on its sign. In shear flow the colloidal rods orientate progressively towards 0${}^{\circ }$ as the deformation rate magnitude increases. Our results decouple the effects of shearing and extensional kinematics at aligning colloidal rods, establishing coherent guidelines for the manufacture of structured soft materials.

References in corpus (5)

• Effects of particle stiffness on the extensional rheology of model rod-like nanoparticle suspensions
• Dynamic characterization of cellulose nanofibrils in sheared and extended semi-dilute dispersions
• Dynamics of individual Brownian rods in a microchannel flow
• The connection between shear thinning and biaxial orientation for quasi-ideal rods
• Reentrant transition in the shear viscosity of dilute rigid rod dispersions

Cited by in corpus (4)

• Alignment of colloidal rods in crowded environments
• How do polymers stretch in capillary-driven extensional flows?
• Flow birefringence of cellulose nanocrystal suspensions in three-dimensional flow fields: revisiting the stress-optic law
• Stress field in the vicinity of a bubble/sphere moving in a dilute surfactant solution