Science AMA Series: We are chemical engineers at North Carolina State University, working on non-Newtonian fluids, soft matter, and biomaterials. We test out your favorite ideas with real experiments and report back in Part 2 of this virtual lab event. AUA!

Abstract

Ever wanted a real material scientist to test your favorite ideas/hypothesis? This is your chance!

What is a non-Newtonian fluid or soft matter? The hydraulic press channel has a great video showing what happens if you crush cornstarch suspensions. Shampoo and espresso are all non-Newtonian. Our blood, mucus, and joint fluids are all non-Newtonian too! Soft matter are things like plastics, silly putty, gelatin... even soil can be considered a kind of soft matter. They really are everywhere!

The Hsiao Lab is an experimental soft matter group in the Department of Chemical and Biomolecular Engineering at North Carolina State University. Last year, we showed /r/science that coffee, amongst other materials, is actually a non-Newtonian fluid that has weird liquid properties. We are hosting a new Reddit event which will consist of two phases. This first part will allow Reddit users to ask questions about any curiosities or ideas that they would like us to test. Our group members will help you refine your questions into a way that we can address.

In our earlier AMA, /u/slp50 asked us if his/her idea using non-Newtonian fluids to build speed bumps will work. That was a great question, and we are going to design an experiment to test this!

We want you to come up with creative questions that can be tested in our lab. We will collect these questions and discuss with you ways to frame them in a way that can be tested within reason. Part 2 is another AMA event where we will release our answers in the form of pictures or videos. This will probably occur a month after the first AMA to allow us to purchase materials and perform tests.

Edit 1: It will help us a lot if you can think specifically of an idea, instead of a very broad question, that you want us to test! Bonus points if it is a cool idea related to everyday life.

Edit 2: Thanks for all the questions! We are going through them as fast as we can. These are some experiments that we designed thus far to test your ideas:

/u/Cronanius wants to know if non-Newtonian fluids could be used to separate particles in geology. We will have a tank filled with different types of fluids and record how they fall through the fluids.

/u/bangbangIshotmyself wants to know what happens when two non-Newtonian fluids collide. We don't really know either, although we think some weird fingering phenomena might appear. We will record how jets of fluids behave when they fall at different velocities into a tank of the same fluid.

/u/ittimjones has this idea that maybe sound waves can be directed at parts of the fluid to make only certain spots harden. We have just the equipment (sonicator) to test this out!

/u/voilsb wants to look at the fluid properties of melted cheese. We'll be sure to prepare lots of grilled cheese on our rheometer.

Edit 3: Lots of people have asked if shear thickening fluids are resistant against explosives, stabs, athletic injuries, or being shot at. All great ideas! Because these are somewhat violent activities (nonlinear deformations), we may not be able to test them all - but we may be able to do a few experiments in a somewhat controlled fashion.

Edit 4: Thank you all for the fantastic responses! We are signing off for the evening and will be compiling your questions. Keep a lookout for part 2 of our AMA where we tell you what happened in those experiments! - Lilian Hsiao, Alan Jacob, Daniel Vasquez

I will phrase this test idea as a question: can you use flowing, non-newtonian fluids to more effectively separate variably-sized particulate by density (analogous to gold panning) than standard fluids (like water) or "dense fluids"?

Normally, to get very accurate density separations in [glacial/fluvial] till samples, [quaternary geologists] would use buoyancy separation techniques via "dense liquids", which I'm sure you know are often nasty and toxic. There are less accurate separation methods that use flowing water, but water's relatively low density and propensity for turbulent flow (at useful velocities) prevents it from being widely used for this purpose. A clever flow technique that used a non-toxic (or at least non-volatile) non-newtonian fluid would probably be pretty welcome among that scientific community. Cool AMA!

Edits for clarity.

Cronanius

I will start off by saying that studying this excellent question is worthy of a journal article.

How does one determine the density of a solid material? Toss it in a fluid of that density and see if it floats or sinks. It floats? Try a lower density fluid. Repeat until the solid does not float or sink. We actually do this in our lab to determine the density of particles.

In scientific terms, the speed at which a solid sediments is determined by its size, density difference with the fluid, and the fluid's viscosity. A non-Newtonian fluid has different viscosity at different speeds; so, a particle will fall much more quickly through a shear thinning fluid as compared to standard fluids. The timing of the falling would have to be accounted for.

So in short, yes - non-Newtonian fluids absolutely could be used to separate particles. However, they will be more complicated to administer, especially in the field.

We will definitely try tackling this question! We will start by measuring the sedimentation velocity of small particles in different types of fluids (say, two Newtonian fluids with different viscosities and two non-Newtonian fluids with different changes in the viscosity when speed differs) and report back our results.


I will phrase this test idea as a question: can you use flowing, non-newtonian fluids to more effectively separate variably-sized particulate by density (analogous to gold panning) than standard fluids (like water) or "dense fluids"?

Normally, to get very accurate density separations in [glacial/fluvial] till samples, [quaternary geologists] would use buoyancy separation techniques via "dense liquids", which I'm sure you know are often nasty and toxic. There are less accurate separation methods that use flowing water, but water's relatively low density and propensity for turbulent flow (at useful velocities) prevents it from being widely used for this purpose. A clever flow technique that used a non-toxic (or at least non-volatile) non-newtonian fluid would probably be pretty welcome among that scientific community. Cool AMA!

Edits for clarity.

Cronanius

Very interesting idea, We intend to so some experiments in this direction. We will drop a ball through different fluids, newtonian and non-newtonian, and let you know how it works out !!!


Hi there,

Thanks for doing the AMA, I really like this idea of the virtual Lab. I am actually a studying chemical engineer and am glad to see some doing an AMA.

Anyways since learning more about fluid dynamics I've been curious as to what would happen when two non-Newtonian fluids collide with each other at different velocities. I'm also curious how a few other variables effect the outcome, such as temperature, density, and viscosity.

Thanks again!

bangbangIshotmyself

Hello! Let us try to examine what you are asking a bit more closely, so we can design the appropriate experiments.

Do you mean if there is a way to videotape what happens if two streams of cornstarch water hit each other straight on, at different viscosities? When non-Newtonian fluids "collide", it is really the time scale of the flow (how fast it flows) and the time scale of relaxing (how fast the things inside the fluid can rearrange themselves) that determine what we end up seeing.


Hi there,

Thanks for doing the AMA, I really like this idea of the virtual Lab. I am actually a studying chemical engineer and am glad to see some doing an AMA.

Anyways since learning more about fluid dynamics I've been curious as to what would happen when two non-Newtonian fluids collide with each other at different velocities. I'm also curious how a few other variables effect the outcome, such as temperature, density, and viscosity.

Thanks again!

bangbangIshotmyself

Hello

Scientists have already investigating the interfacial tension when two non newtonian fluids collide with each other. We could perform this experiment by injecting a dyed corn starch solution into a tank of undyed cornstarch and see what happens!! We will be interested to show what happens!!


Might be a dumb question but it can't hurt to ask.

How does something like Oobleck act at different atmospheric pressures? Ignoring all the obvious reasons we can't do it, If I had a perfect sphere that I could interact with on earth, and one on venus, what would be the difference in the typical experiments we do with them (Running and jumping on it, punching it, etc).

Thanks!

Hive_Tyrant7

That's funny! We have done activities with high school students where they jump on a cornstarch pool. We're not prone to violent outbursts though, so we don't typically jump on our experiments. :)

Oobleck is basically cornstarch particles suspended in water. Water is generally incompressible (water is still water at the bottom of the Mariana trench where the pressure is 1000x atmospheric pressure). So, we don't expect ooblect to behavior any differently at that pressure, although maybe the softer cornstarch particles could become mushed.


Right up my alley. I study Chemical Engineering and fluid mechanics particularly interest me. Just a quick question: Do you use Computational Fluid Dynamics (CFD) as part of your experiments? Thanks for doing this AMA!

lil_Mikko

We do not typically use CFD, simply because we focus more on bulk material properties and correlations to microstructure. However, CFD is very useful in modeling the flow fields of complex fluids if the constitutive relations are known. We may use software like Comsol in the future to look specifically at things like emulsions and hydrogels flowing.


I am so excited to see the results of the speed bump experiment! Finally internet (almost) fame!

slp50

I loved your idea in the last AMA. We are going to fill balloons with cornstarch suspensions and drive over them with remote controlled cars. Then, we are going to do some precise measurements to determine the fluid properties that allows you to control the speed at which the speed bump becomes uncomfortable. Lets see how far we can go with it!


Are any non-newtonian fluids particularly exothermic or endothermic when undergoing excess stress (behaving almost like a solid)? If so, can this be harnessed for a heat exchange of some sort, such as some sort of radiator?

edubsington

Unfortunately they are not exothermic or endothermic hence cannot be harnessed for heat exchange.


What are needed to set up soft matter science lab? What equipment do you guys have, what do you mostly use, and what do you wish to have in the future?

eycoli

We heavily use two workhorse instruments: a rheometer (measures stresses in fluids) and a high speed microscope. We will soon have an instrument that brings the two together, so you can look at materials deform while measuring stresses.


This is awesome, I actually just CODA'd into ChemE at nc state, got my acceptance letter a couple weeks ago. I can't think of a question off the top of my head but I love the idea. Can't wait to see what questions you answer.

thumpas

That's very kind of you! Anyone can ask questions in this AMA, so if you think of something cool related to daily life, that is even better. I will teach CHE 205 in the Fall, looking forward to meeting you and all of your classmates! - Lilian Hsiao


How much silly putty does it take to stop a .22 bullet? How does that amount compare to ballistic gel?

justinsayin

Hello!! It might not be a good idea to use silly putty in place of a ballistic gel because sillyputty flows with time. If you leave a ball sillyputty(literally roll it into a ball) on your table it will flow and lose its shape in a few hours.


I recently had a jar of peanut butter confiscated at airport security as a liquid. What are your thoughts on this?

EyeTea420

Peanut butter yummy :). Technically peanut butter is a Non Newtonian fluid which means it is a liquid that flows very slowly.


So, when trying to create an organ for transplant (still just being researched), scientists can get say, a liver, from a pig and then wash away all the cells, leaving behind a translucent scaffold.

Now, one of the main problems is trying to recreate all the blood vessels in the scaffold. You can pump cells through the scaffold organ but they don't actually adhere to the vessel linings very well to start reforming the blood vessels. Without intact blood vessels, the organ will never survive, so this is a very important step.

Now, do you think you could put these cells in some type of fluid, that when pumped through small tubes (scaffolds of the blood vessels), a fluidic force could then push the cells uniformly onto the scaffold tubular walls so that they can properly adhere? Maybe add in sound or what have you to modify the forces.

It's a very loose thought but I wondered if you had any concrete ideas to test as proof of concept. Maybe not with cells in a fluid, but some other kind of soft matter akin to it with plastic tubing.

IthinktherforeIthink

Hello.

You have pointed out an interesting and difficult application. In theory if you pump a yield stress fluid (a fluid that has yield stress when it does not flow could stick onto vessel lining. Such a material will have the consistency of a paste. The other way to do it is manipulating physical forces or chemical forces between the fluid and the vessels. For example surface tension of fluids could lead to capillary forces. We could try to brainstorm in this general direction but keep in mind that it is not trivial to solve such issues for such a specific application


I wonder if non-newtonion fluids could be used in helping with earthquakes? Where a base of liquid could be at the structures base, and when the quakes start the fluid hardens taking stain of the buildings structure. This would help with aftershocks and overall damage to the building if the substance was able to absorb enough of the shock.

duckman42

Hello. That is a cool idea but the flaw is that if you have an earthquake. You want the building to move with quake. That is the best way to dissipate the energy. If the building stays stiff due to inertia of the building it will collapse during the earth quake. So it might not be a good idea to put non Newtonian fluids at base of building as of yet. Moreover if we put a building on top of a fluid the building will sink.


Best restaurant in downtown Raleigh?

Novatronix

Mami Nora's or Alpaca! Best ever.


Could a thinner, lighter, non-newtonian filled boxing/fighting glove be designed? The idea being that during impactless movements like grappling, the glove would be soft and flexible, but upon punch contact the glove would become rigid and allow a higher transfer of kinetic energy to the target of the blow.

cosmos_jm

That sounds like you wanna hit somebody!


non-newtonian fluid ideas off the top of my head

  • bullet proof armor

  • blast proof bricks

  • car bumpers

  • phone/tablet/laptop protective sleeves/cases

  • athletic helmets (other padding too?)

  • [IDEA] Can the hardening be controlled via a small vibrating motor or high pitched sound waves? If so, you could maybe use it as a sort of access control where if certain variables are met, a hardened structure is formed in select locations?

ittimjones

Your idea on controlling the hardening in a local area has a lot of merit. We are currently looking into this research topic with light instead of sound waves to control hardening, but we will test your idea with sound waves because we have just the equipment to show you if it works!


Could you mix a shear thickening non-newtonian liquid with concrete and check if it would harden enough to stay the way it was during the time force was applied to it? Might make interesting shapes.

Juxtys

Concrete(before it hardens) take a shape of its own. Non-Newtonian fluid is not required for that purpose . Hence concrete is a non- Newtonian fluid by itself .


Hey guys! It's awesome to see some chemEs working on cool stuff like this.

My question is what is the maximum sheer stress different non-newtonian fluids can undergo before fracturing, like a typical solid ? Does it even fracture? And, once it does, how long does it take to return back to the liquid state?

Thanks and have a wonderful day!

ssimarsawhney

Toothpaste is a typical example of Bingham fluid which is a kind of non-Newtonian fluid. Every time before you brush your teeth, you have to squeeze the toothpaste out. If you don't apply stress on the toothpaste, it won't flow at all. Consider the stress difference in this case and you will find out that it's pretty small. There's no actual fracturing in the fluid but some micro-sized changes. For those kinds of Bingham fluid, once you release the stress, the fluid immediately becomes solid like just like your toothpaste.


Just a question- How would a nanofluid be classified among newtonian and non-newtoninan fluids?

cdhawan4314

You can do a rheological test on the fluid. If the viscosity changes with the shear rate, then it's a non-Newtonian fluid. If the viscosity remains constant, then it's a Newtonian fluid.


Can you make non-newtonian ferrofluids? Are they as pretty as I'm imagining?

patch47000

Yes you can - and since ferrofluids are magnetic particles suspended in a liquid, they are already non-Newtonian. You should look up ferrofluid lamps!


I just want to know what happens when you stick a typical boat engine in a non-Newtonian fluid and start the propeller. Could you boat over a sea of non-newtonian fluids? Can you think of a better mean of propulsion than a propeller? What would be a good shape for the hull?

Surcouf

If your sea exhibits a shear thinning behaviour it will be a good idea to use a propeller at high speeds and enjoy boating. On the other hand if the fluid exhibits shear thickening behaviour it might not be a good idea to do boating :)


What's the coolest doable at home think you can make with non-newtonian fluids besides makimg one?

ltcortez64

You can buy silly putty on Amazon and play with it!


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