Abstract
Many real-world industrial processes involve non-spherical particles suspended in a fluid medium. Knowledge of the flow behavior of these suspensions is essential for optimizing their transport properties and designing processing equipment. In the present work, we explore and report on the rheology of concentrated suspensions of cubic-shaped colloidal particles under steady and dynamic shear flow. These suspensions exhibit a rich non-Newtonian rheology that includes shear thickening and normal stress differences at high shear stresses. Scalings are proposed to connect the material properties of these suspensions of cubic particle to those measured for suspensions of spherical particles. Negative first normal stress differences indicate that lubrication hydrodynamic forces dominate the stress in the shear-thickened state. Accounting for the increased lubrication hydrodynamic interactions between the flat surfaces of the cubic particles allows for a quantitative comparison of the deviatoric stress in the shear-thickened state to that of spherical particles. New semi-empirical models for the viscosity and normal stress difference coefficients are presented for the shear-thickened state. The results of this study indicate that cubic particles offer new and unique opportunities to formulate colloidal dispersions for field-responsive materials.
Highlights
The viscosity of suspensions at low particle concentrations can be expressed as an expansion in the particle volume fraction as:[1]Zr = 1 + kEf + kHf2 + higher order terms (1)In the equation above, Zr is the relative viscosity, f is the volume fraction, and kE and kH are the Einstein and Huggins coefficients expressed in terms of volume fraction, respectively
There is no theory for the value of the Huggins coefficient for cubic particles with which to compare
This work expands our understanding of the flow behavior of suspensions of cubic particles in a Newtonian fluid at low
Summary
The quadratic term in the viscosity expansion accounts for pair interactions between particles, and the value of the Huggins coefficient can reveal information about the nature of the interparticle potential.[3] Batchelor and Green[4] calculated the value of the order f2 coefficient to be 5.2 for random suspensions of hard-spheres in shear flow. This was refined to a value of 5.0 by Wagner and Woutersen,[5] and the introduction of Brownian motion between particles increases the value to 6.0.6. Simulations by Morris and co-workers have demonstrated that the introduction of particle inertia[18,19] and interparticle friction in addition to lubrication hydrodynamics can enhance the shear thickening response.[20]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
