Microstructure in Gelling Systems (Michigan)

Author Last Name: 
Michael J. Solomon
Report Type: 
Research Area: 
Wet Systems
Publication Year: 
Publication Month: 
United States

The microstructure of gelled colloidal systems is a key determinant of their rheological

response. In this project, we addressed three aspects of this critical problem. In the first

part, we identified high contact number, stress bearing configurations in colloidal gels

that had been subjected to non-linear step strain, and determined that these stress bearing

clusters are predictive of the non-linear elasticity of the gel. The idea, borne out by

analysis of the experiments, is that the hydrodynamic interaction of a fluid of jammed,

stress bearing clusters is the principal determinant of the post-yield rheology of colloidal

gels. In fact, the abundance and size of these stress-bearing clusters could likely be

identified from a measurement of the rheological response. In the second part, in

collaboration with the Furst group at the University of Delaware, we developed a model

colloidal system in which force, structure, and rheology could all be measured, so that the

relationship between these three properties could be better understood, especially with

respect to modeling the important rheological quantity of the yield stress. This model

system needed to balance a number of constraints related to refractive index matching

and density matching. We found a particular condition that satisfied all the constraints,

and therefore opens this area to fundamental research. In a final project, we observed

that we could produce colloids with controllable roughness. We studied the effect of this

variable on a number of rheological properties of colloidal suspensions. We found that

the shear thickening response was most affected by colloid roughness.