Sticky, slippery, slimy: The Rheology Zoo is totally touchable

MechSE assistant professor Randy Ewoldt was awarded a National Science Foundation (NSF) grant for his proposal, “Hagfish Defense Gel and the Rheology Zoo.” The grant, awarded through the “Broadening Participation Research Initiation Grants in Engineering (BRIGE)” program, will give his project $175,000 over two years.

The BRIGE program is designed to promote the development of early career faculty, who show promise of becoming champions for diversity and broadening participation throughout their careers. It is part of a larger “Broadening Participation in Engineering” program at the NSF to support the development of a diverse and well-prepared workforce of engineering graduates.

Ewoldt hopes to better prepare students for the next stages of their education through his project, “The Rheology Zoo.” Rheology is the study of the flow of materials that behave and deform in interesting or unusual ways. While there are no living creatures in this zoo, there are many interesting and unique materials. Some of them are familiar to the everyday consumer, such as Silly Putty, aloe gel, Play Dough, frosting, and peanut butter.

“These materials can be complex in different ways, and that’s hard to understand if you just see pictures or videos,” Ewoldt said. “But if you feel it with your hands, you can really tell.”

The theme of the zoo is “hands-on research,” where students can develop intuition about rheologically interesting materials in a first-hand way. They can study properties such as viscosity and elasticity, and study the structural causes behind these properties inside the materials.

“The big idea is to have a tactile learning entry point for students of all types,” Ewoldt said. “I want my graduate students who are taking my advanced, upper-level classes to have hands-on intuition of what these materials are, and it’s also a good entry point for undergraduates to give context to the courses they’re taking like fluid mechanics and solid mechanics. If you see materials like these, and you think about both fluid and solid concepts in one material, I think it gives more context to what you’re learning.”

In its early stages, the zoo will simply be a collection of materials in a designated space in Ewoldt’s lab, where students will be invited to complete projects studying the materials. Once there is an appropriate and diverse collection of strange materials, Ewoldt’s vision is that the zoo will include a mobile unit that can be taken to different campus locations.

“In its best embodiment, the Rheology Zoo will be a classroom in a box or on a cart that I can take across campus,” Ewoldt said. “It will be structured learning for someone who comes at rheology and complex materials having never seen it before. But if they can accelerate their learning with hands-on demos, they can also accelerate their creativity to be thinking about these weird materials in a product design, for example. Having this layer of open-ended creativity is a big intention, so people can learn about something they haven’t thought about before, in ways they haven’t thought about before, and then be creative with that new information.”

Towards this effort, Ewoldt is working with several programs at Illinois to create a research experience related to the Rheology Zoo for incoming undergraduate students to the College of Engineering.

One of the “all-stars” of the Rheology Zoo, and a subject of Ewoldt’s own research, is a material called hagfish defense gel. The hagfish, an eel-shaped marine animal, secretes a small amount of material into the surrounding seawater when attacked. This material swells to a gel with a volume much larger than its original state. The quick and enormous change in volume, which Ewoldt calls “heroic,” is on the order of 10,000. As predators try to consume the hagfish, this swelling gel chokes the predator and allows the hagfish to get away unharmed.

The material the hagfish secretes is incredibly absorbent, and completely different from any other kind of gel material that has been studied, or that mankind has tried to produce. It appears to be at least partially made of a mucin-like material. Mucins are polymers found in snot, tears, saliva, and other slippery/slimy things found in nature. But it also consists of long threads that, when the gel absorbs water, somehow stretch and form a unique network that holds the gel together despite the volumetric change.

“We want to write out our physical and mathematical understanding of relating the structure to the macroscopic mechanical properties of the material,” Ewoldt said. “And if we can write that appropriately, and demonstrate that understanding, it means that we can eventually start designing materials based on this mechanism. If we’re successful in outlining the structure rheology models in the appropriate way, it will set the stage for how to make that property result from materials that are based on fibers and sticky molecules that stick things together.”