Experimental Photo

Have you ever wondered why marshmallows, while solid, seem to behave a little like a liquid when you chew them?

Marshmallows are made up mostly of polymers:  a collagen gel network to be exact.  Unlike traditional materials, polymers have a interesting trait known as a second order phase behavior.  You probably know about the three states (or four) of matter:  solid, liquid, gas (and plasma) but there are materials that have an additional distinction.  These polymer materials have a transition we call the glass transition.  When a solid at cold temperatures, they act like a glass and are easily broken.  This is the “glassy state.”  At high temperatures, they are in their “rubbery state” and are easily deformed.  In the photo above, I am cooling marshmallows down with liquid nitrogen (-321 degrees F!) to show how they transform into their “glassy state.”  You can eat them too!  They are very similar to the marshmallows you’ll find in Lucky Charms Cereals as those are “freeze dried,” a process where the marshmallows are first frozen but the water is then sublimated off.

 

 

Research Descriptions

Materials Science and Engineering Audience:

Aqueous gels are the cornerstone of this research.  Thermoreversible gels and hydrogels are the model systems.  One of the gel systems used involves a dendrimer created almost three decades ago.  This dendrimer forms thermoreversible gels at very low weight percentages with a transition temperature not much higher than room temperature.  This molecule is used as a low-cost model system for amyloid beta studies as well as an self-assembly agent for other rod-like macromolecules.  Currently, this system is being used to study the transitions in lyotropic liquid crystals.

General Audience:

Imagine a mountain lumberjack with a lot of logs and only a stream to get those down the river.  What happens as more and more logs are placed in the stream?  At first, the logs would flow smoothly since they would have sufficient spacing.  As more logs were added to the water, the flow would slow but eventually there would be so many they’d have no choice to line up and flow down the river side-by-side.  This demonstrates the principle of lyotropic liquid crystals.  As more and more rod-like particles are added to a liquid they eventually have no choice to line up.  In our research we study systems like these on the nanoscale to understand how these systems flow and interact with light.

 

Scientific Communication Workshop

Why does Jell-O transform from a flowing liquid to a jiggly, delicious treat?

It all has to do with the formation of a gel network.  I study these networks and their structure on the molecular level in my PhD.  I look at a variety of water-based gel materials including pNIPAM, arborols, and aqueous lyotropic liquid crystals.