# Presentation: 555467

## CAREER:  Static Properties and Dynamical Behavior of Jammed SystemsEric R. Weeks, Emory University,  DMR 0239109 & DMR0603055 

- Unlike liquids, glasses aren’t comfortable in confined spaces.  We study pastes made of tiny plastic particles in a liquid, a model system which acts like a glass when the particle concentration increases.  Using an optical microscope, we view particle motions in 3D.  When the sample is confined between two parallel plates, particles move slowly and the sample becomes even glassier.  These experiments help us understand earlier work done with thin polymer films and other glass materials.
- This work was published in *Phys. Rev. Lett. *(July 13, 2007) and featured in Physical Review Focus (July 24, 2007).

- 2 and 3 micron diameter plastic particles in a paste.  This is a simple model system.  The particles in the sample are analogous to atoms in other materials.

- 3D image of 2 micron diameter particles in a similar paste.  From these images, we can identify particle positions and follow their motion in 3D.

- 10 m

**Notes:**
Are glasses merely extremely slow liquids? Liquids take on the shape of their container. In our work, we show that unlike liquids, glasses aren't comfortable in confined spaces.  We study colloidal samples composed of plastic particles in a liquid, a model system which acts like a glass when the particle concentration is increased. To produce our 3D pictures, we use an optical confocal microscope.  When the sample is confined between two parallel plates, particles move slowly and the sample becomes even glassier. As the sample particle concentration is increased toward the glass transition point, we observe confinement-induced slowing at larger plate separations. Our previous research has shown groups of particles in dense suspensions move cooperatively, similar to how molecules move in regular molten glasses as they are cooled. Our work suggests glasses are solid-like because these groups can't move when the sample chamber is thinner than the typical size of these groups. These experiments help us understand earlier work done with thin polymer films and other glassy materials, but as we use particles rather than atoms, we get to directly see how confinement influences the glass transition.

Our paper was featured in Physical Review Focus, which picks approximately one article per week from Physical Review to highlight.

## CAREER:  Static Properties and Dynamical Behavior of Jammed SystemsEric R. Weeks, Emory University,  DMR 0239109 & DMR 0603055 

- Two undergraduates (Carolyn Nugent and Hetal Patel) led this work, with additional help from a graduate student (Kazem Edmond).  Nugent is now a graduate student at UCLA, Patel is currently in medical school, and Edmond is continuing this project at Emory.  In the past five years, 15 undergraduates and 12 graduate students have worked in our laboratory, and learned skills such as computer programming, image analysis, microscopy, and chemistry lab skills.
- Our group in Summer 2007 is shown at right; the PI is at the front-right.

**Developing new software tools:**
- We maintain a website with free programs for particle tracking, along with a tutorial.  We have recently expanded this website to include software for tracking particles in 3D.  Our software is used by many other research groups around the world.

**CAREER:  Static Properties and Dynamical Behavior of Jammed Systems**Eric R. Weeks, Emory University,  DMR 0239109 & DMR 0603055** **

**Notes:**
We work with squishy materials such as colloids, foams, and emulsions.  Common examples of these are toothpaste, shaving cream, and mayonnaise, respectively.  Our primary experimental technique is microscopy.  Thus our work with these squishy materials is hands-on and visually appealing, and it is easy to get undergraduate students involved.  Many of these students attend national meetings such as the American Physical Society March Meeting, and give ten-minute talks on their work there; this has included about half of the undergraduates and nearly all of the graduate students.  Many of the undergraduates earned their degrees and have gone on to a variety of paths, including graduate school in physics or chemistry, medical school, and also directly into industry.