Shear dilatancy in dense emulsions

When you twist a solid cylinder, its height spontaneously changes. This is one example of shear dilatancy, a well known but poorly understood nonlinear mechanical effect. Shear dilatancy occurs in dense dispersions such as gels, grains, pastes, foams, and emulsions – each of which has important applications in process technology. Nevertheless, we cannot reliably predict the amplitude or even the sign of shear dilatancy. While most materials expand, others contract. Therefore, the fundamental and unresolved challenge is to identify a minimal set of physical mechanisms responsible for shear dilatancy in dense dispersions.

This project will test the hypothesis that shear dilatancy is the result of a competition between two opposing effects. The first is the tendency for dilation to induce tension, and thereby increase shear stiffness. The second is the tendency for dilation to change topology, and thereby reduce shear stiffness. We will motivate this hypothesis using novel calculations in nonlinear continuum mechanics, and then to test it using simulations of a minimal numerical model for attractive emulsions, benchmarked with recent experimental data.

This project is financed by NWO.

Chair:
Multiphase Systems

Involved People:
Dr. B.P. (Brian) Tighe