Exploiting the Malleability of Disorder to Design Functional Materials

Abstract
Systems with complex energy landscapes, such as glass-forming systems, have far more variation in their properties than those with simple ones that readily crystallize. This natural variation can be pushed even further by design, allowing us to tune in unusual properties and novel functions into materials. For example, most materials that are stretched in one direction tend to shrink in the orthogonal directions. Materials that do the opposite and expand in the orthogonal directions when stretched are “auxetic,” and have attracted attention for applications such as high energy absorption. We have found that mechanical spring networks can be tuned easily and naturally to the extreme limit of auxetic behavior, and can even be trained to this limit. Likewise, we have shown that properties common in living matter, such as the ability of proteins (e.g. hemoglobin) to change their conformations upon binding of an atom (oxygen) or molecule, the ability of the brain’s vascular network to send enhanced blood flow and oxygen to specific areas of the brain associated with a given task, can be designed or trained into disordered systems using similar principles. The ability to design properties and functions further gives new insight into the relation between microscopic structure and function that may help us both to understand living systems and to design new biologically-inspired materials.