When mixing granular matter, order among disorderMixing liquids is easy, or at least scientifically

When mixing granular matter, order among disorder

Mixing liquids is easy, or at least scientifically understood: a drop of food coloring will eventually mix into a cup of water through diffusion, and a dollop of cream can be mixed into coffee with a spoon through what is called turbulent mixing.
But what if the material has the properties of both liquids and solids, which is the case for materials like concrete, paint, and sand? Called yield stress materials, these mixtures can both flow like liquids and remain still like solids.
Understanding how these materials mix has implications in industries such as pharmaceuticals and concrete manufacturing, but little is still known about how to best mix them.
In a new paper in Nature Communications, Northwestern Engineering professors find that mixing yield stress materials creates both mixed and non-mixed regions, providing a fundamental beginning to understanding how to best design mixing protocols. Julio M. Ottino, Paul Umbanhowar, and Richard Lueptow served as the paper’s co-authors.