Structure and flow behavior of cubic nanoparticle suspensions
Rajesh Mallavajula (Cornell University), Lynden Archer (Cornell University), Donald Koch (Cornell University)
Complex Fluids: Suspensions, Emulsions, and Gels
Tue 2:40 - 4:00
Barus-Holley 160
Shape of nanoparticles is one of the important factors that determine their suspension flow behavior. Cubes are the simplest polyhedral shape that presents unique geometrical characteristics such as flat surfaces, corners, edges and yet no aspect ratio. We have studied the effect of these features on the flow behavior of cube-shaped particles using both theory and experiments. At low volume fractions, the average stress in the medium was obtained as a function of the orientation of cubes using a finite element method. It is found that the sharpness of the cube edges increases the stress. The value of intrinsic viscosity, defined as the first order correction to the suspension viscosity due to particles was evaluated as 3.1. At finite particle volume fractions, Brownian dynamics simulations were carried out to study the structure and flow behavior of these suspensions. Simulations were performed over a wide range of volume fractions and Pectlet numbers. For volume fractions less than 0.25, cubic particles are found to exhibit analagous rheology and structure to a suspension of spherical particles circumscribed over the cubes. These insights from theory are compared with observations from experiment. Specifically, we have synthesized cubic nanoparticles of varying sizes, size distributions and surface chemistries and characterized their dilute and finite volume fraction suspension rheology. Spherical particles of identical chemistries and similar sizes were also synthesized to compare their properties with the cubic particle suspensions. The intrinsic viscosity for the suspension of cubic particles was measured to be 3.1±0.2, in excellent agreement with the theory. Rheological properties were measured at low, moderate and high volume fractions and these results are also compared with the theoretical predictions.