My project in the Corwin Lab this year concerns jammed granular systems.

But what are granular materials?

We're all familiar with the three phases of matter: liquids, solids, and gases, but it turns out a lot of materials can act as two of those. For example, grains of sand act as a solid when not in motion, but can also behave similarly to a liquid when poured.

These granular materials are all around us, from ice to coal to petrochemicals.

So what's a jammed granular system?

A jammed granular system is exactly what it sounds like. Similar to 5:30 pm traffic jam, it's a point at which, no matter how hard anyone tries from any side, you (the particles, in this case) can't be moved (rearranged).

Jammed granular system.

Jammed granular system.

why do you care?

It turns out that these granular materials have incredibly complex mechanics, which makes them interesting to scientists. 

Okay, but what about the rest of the world? Why are jammed granular systems important to everyone else?

Since granular materials are ubiquitous, a lot of industries are involved with them, including aerospace and agriculture.

In the agricultural industry, when grains are being processed, only a certain amount of them can fit into the loading hopper at a time.

Loading hopper. Courtesy of www2.donaldson.com

Loading hopper. Courtesy of www2.donaldson.com

However, if the entrance speed of the grains into the hopper is larger than the exit speed, the grains will jam the system. These jams can cost companies significant amounts of time and money to resolve. Understanding the granular physics of jammed systems could help the industry become far more efficient.

Planetary exploration is also affected by granular materials. NASA has conducted extensive research into the risks granular materials pose for lunar and Martian missions, but that research isn't enough. 

Courtesy of wikipedia.org

Courtesy of wikipedia.org

See, the problem is this: We don't know how our vehicles, our shoes, or our suits are going to hold up against the terrain. Vehicles, for example, need to be able to maintain traction while traveling on the Martian surface, especially on steep inclines. This means we need to understand how the soil will pack under the tires. 

If a vehicle or its tires fail on Mars, it's going to take AAA a lot longer to help them than it does when you're stuck on I-5 with a flat. So, in this case, it isn't so much about money. It's about understanding how these systems work so that we can build the best equipment possible for the astronauts who go to Mars or back to the Moon. 

Great. So, we know why granular materials are important to study now, but how do we do that?

One way is to model the system. My lab is modeling a jammed granular system with oil-in-water emulsion via microfluidics.

What's that?

We are using a microfluidic droplet generator, which creates really minuscule droplets of whatever we put in there.

The two channels on the outside have a water-based solution flowing through them, while the channel in between has a silicone oil solution infused with red dye.

Lucky for us, oil and water don't mix, so when they come to flow together (in the middle of the chip down below), the water cuts the oil off into monodisperse (equally-sized) droplets.

We drop them into a chamber to be imaged. The red dye helps us here so we can see the outlines of each of the droplets. Once we reach that critical particle concentration, we study the properties of the jammed system.

what properties are you looking at?

We're looking at the forces between the droplets, the contact length of the shared area of the droplets, and the average number of droplets each one touches. This is the experimental side of physics, so we want to confirm or reject some recent theoretical predictions. However, we also want to see new things, things that may not have been theorized yet.

where are you now in your research?

Still in the data collection phase. It's ended up being harder than we thought to set this experiment up and collect data, but, hey, that's science. We'll get there.

 

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