Brian P. Tighe - Research

I study the physics of a broad class of materials familiar from everyday life. Sand piles, grain silos, shaving foam, mayonnaise, window glass, and even cars on a highway can all, at some level, be understood as disordered collections of particles that interact simply by getting in each other's way. In dense systems, this can lead to a "jamming/unjamming transition" -- something most drivers know all too well. Much like when a traffic jam turns the highway into a parking lot, materials that jam or unjam go from a flowing, fluid-like state to a rigid, solid-like state. It's reminiscent of freezing and melting, but the transition isn't governed by temperature.

Because foams, emulsions, and sand are disordered and because the bubbles/droplets/grains are too large to rearrange under thermal fluctuations, these materials defy description with many of the the textbook methods of statistical and solid state physics. My work involves developing new theoretical and numerical methods and exploring their consequences. To date I have focused on two related topics. First, I try to understand the heterogeneous (and lovely) networks of forces between grains in a sandpile -- see the central image above, made from a special type of grain that lights up when it is squeezed. More recently, I have become captivated by the rheology, or flow properties, of bubbles and droplets, like in the upper-left image on this page. Foams can be solid-like but will flow: think of a dollop of shaving foam that can be spread on your skin. I have found that a detailed understanding of the solid-like state allows one to predict important properties of the flowing state.

Flowing foam movie courtesy the van Hecke group at the Universiteit Leiden.
Images of photoelastic grains courtesy the Behringer group at Duke University.