READING #4 - Jamming and Disordered Materials
Piotr Habdas and Eric R. Weeks, Physics Department, Emory University, Atlanta, GA
In our lab, we use various microscopy techniques to look at small colloidal particles (few thousands of a millimeter in diameter) suspended in a liquid (just like Robert Brown almost 200 years ago). We study how their motion changes when the particle concentration is increased. Why is this important and cool? Well, below there is a copy of an article which deals with jamming on various scales - from traffic jams to molecules jamming in a glass-forming liquid. Our colloidal suspensions are a good system that exhibits such jamming behavior and they have a big advantage over regular glasses. We can see individual particles whereas in a regular glass the molecules are just too small. Therefore, we hope that our research here helps in some little way to understand the mechanisms which are responsible for the formation of a glass. To learn more click here to visit our web site.
- Small region of phase space - the particles are unable to rearrange; normally Brownian motion lets them rearrange and thus explore many possible configurations ("phase space") Due to crowding the Brownian motion just moves things back & forth in place.
- Canonical example -an example that many people know about
- Continuum elastoplastic theories - theories that don't rely on atoms, but deal with ideas like density, pressure, and viscosity
- Elastic body - a solid material which perhaps is slightly squeezable, like hard rubber
- Infinitesimal force - extremely small force
- Stress - forces that could cause a material to stretch
- Strain - how much something is stretched
- Stress tensor - a mathematical way to describe stresses (forces) within a material, such as places where the material is compressed or stretched
- Isotropic stress - forces that are the same in all directions. For example, gravity is not isotropic because it pulls you downward.
- Respond plastically - this is when something permanently changes its shape. For example, if you have a block of Jello™, you could blow on it gently and it might wiggle, this is an "elastic response". If you dropped it on the floor it would smoosh and break apart; this is a "plastic response"
- Thermal motion - this is the same as Brownian motion