Rheology and Dynamics of Colloidal Superballs

Published

June 9, 2015

Author(s)

John R. Royer, George L. Burton, Daniel L. Blair, Steven D Hudson

Abstract

Recent advances in colloidal synthesis make it possible to generate a wide array of precisely controlled, non-spherical, shaped particles. However, relatively little is known about the role that particle shape plays in the dynamics of colloidal suspensions, particularly at higher packing densities where particle interactions and changes in the microstructure are likely to become increasingly important. We examine the role of particle shape by characterizing both the bulk rheology and micro-scale diffusion in a suspension of pseudo-cubic silica superballs. Varying the packing density $0 \leq \phi \leq 0.40$, we compare the high- shear viscosity and long-time self-diffusion coefficient $D_L(\phi)$ to established hard-sphere results. In dilute suspensions the superball viscosity is nearly indistinguishable from the that of hard spheres, indicating that the hydrodynamic properties of individual superballs are not dramatically different. However, there is a significant difference in the diffusion, with the superball $D_L(\phi)$ decreasing faster with increasing $\phi$. Examining the suspension microstructure, we find that while the hard sphere pair distribution $g(r)$ rises to a finite value at contact $r=2a$, the superball $g(r)$ is shifted to higher distances. This suggests a simple rescaling $\phi \rightarrow \phi_{eff}$ defined by the minimal sphere needed to enclose a superball, which nearly collapses the diffusion results. At moderate packing densities the superballs exhibit mild, continuous shear thickening which differs qualitatively from shear thickening observed in silica spheres under similar conditions.

Citation

Soft Matter

Volume

11

Issue

28

Pub Type

Journals

Download Paper

DOI Link

Keywords

colloids, rheology, diffusion, shear-thickening, shape

Citation

Royer, J. , Burton, G. , Blair, D. and , S. (2015), Rheology and Dynamics of Colloidal Superballs, Soft Matter, [online], https://doi.org/10.1039/C5SM00729A (Accessed December 9, 2024)