# Presentation: 555466

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

- Our laboratory studies “squishy materials” such as foams, gels, and pastes (more formally known as “soft condensed matter”).  We use microscopy to relate the microscopic structure to material properties, such as how deformable a material is.  Recently we’ve studied properties of pastes when they are confined to small spaces.  We find the pastes strengthen and act more like a solid material in such confined spaces.  This system is a model for molecular materials in thin films, which are important for industrial applications such as nanolithography.

- 2 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.

- Microscope picture of droplets of oil in water.  By measuring the droplets’ deformations, we learn how the walls of a confined space exert forces on the droplets.

- 10 m

**Notes:**
The field of soft condensed matter is the study of materials that have properties of both liquids and solids.  This includes common substances such as peanut butter, clay, jello, shaving cream, and hair gel.  The key to understanding these materials is to know how the microscopic structure relates to their macroscopic properties, such as how easy they are to spread, deform, or compress.  We study simple examples of soft materials, such as pastes (solid particles in a liquid) and emulsions (liquid droplets in another liquid).  One of our recent projects examines how these materials behave when they are in confined spaces.  We place the materials in a thin gap between two plates of glass, where the gap thickness can be as small as 10 microns, comparable to the size of the particles or droplets.  We find that the materials become very resistant to deformation, unlike when they are not confined.  It is harder for the particles to move, for example, given that they are constrained by other particles which in turn are constrained by the glass plates – they are like cars trapped in a traffic jam that can’t leave the road.  This matches similar observations of some molecular materials whose properties change when they are spread into thin films.  In our case, we use microscopy to examine the details of why our system changes in confined spaces.  Our work should help explain the behavior of the analogous molecular materials.

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

- We have organized lab tours for home-schooled children to learn about “squishy materials.”  We also show traditional demonstrations of physics concepts.  The field trips are organized by the PI with the help of undergraduates, graduate students, and postdoctoral fellows, all of whom are involved in NSF-funded research.

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

- Postdoctoral fellow Dr. Denis Semwogerere shows a microscopic view of a squishy material

- Putting on gloves to prepare to play with squishy materials

**Notes:**
Squishy materials are quite common once you think about it – food products, soaps, toothpaste, etc.  It’s easy to show children that the materials are fun, and also that they exhibit intriguing properties.  For example, corn starch and water is easy to stir slowly, but difficult to stir quickly.  Clay particles in a liquid can behave the opposite way, appearing like a gel until stirred vigorously.  We have given several lab tours to different groups of children, where we show them the materials and discuss how a physicist thinks about the materials.  (The presentation varies depending on the age of the children, of course.)  We also show them some demonstrations of more traditional physics phenomena, using the lecture-demonstration equipment at Emory University.  The field trips are organized by Prof. Weeks and his lab group, which includes undergraduates, graduate students, and postdoctoral fellows.  The lab group tries to convey the excitement of doing research to the field trips, which is easy to do as both the children and the researchers have a lot of fun at these tours.