8 Things You Didn't Know About Non-Newtonian Fluids

Non-Newtonian fluids are interesting because their properties change when stress is applied, rather than staying the same like conventional fluids. While all fluids have a specific density and can be measured using a hydrometer, non-Newtonian fluids react to stress in different ways. Non-Newtonian fluids have properties that aren’t constant; they change depending on the force being applied. When pressure is applied to Newtonian liquids, they don’t change much and you can see this in the way a car floats on water or how oil won’t drip from a piece of paper if it’s not moving fast enough. Non-Newtonian fluids are so named because they weren’t discovered until after Sir Isaac Newton, but they respond differently than conventional fluids once stress is applied. Here are 8 things you probably didn't know about non-Newtonian fluids.

You Can Tell The Difference Between Newtons And Non-Newtons

Newtonian and non-Newtonian fluids are distinguished by their viscosity and yield stress. Viscosity is the resistance to flow and is described by Newtonian fluids as having a constant viscosity, where non-Newtonian fluids have a yield stress that increases as stress is applied. Non-Newtonian fluids are non-Newtonian because their viscosity is independent of their velocity. Newtons are Newtonian fluids, like water, and non-Newtons are non-Newtonian Fluids.

They Can Be Thicker Or Shorter Depending On Stress

You may have heard the term "jamming" when it comes to non-Newtonian fluids. When a non-Newtonian fluid is in a liquid state but is pressed hard enough, it will solidify into a more solid form. This is called the jamming transition. When you press a non-Newtonian fluid hard enough, it can get thicker. In fact, one of the best examples is oobleck, which is a mixture of cornstarch and water. Oobleck is a great example of how a non-Newtonian fluid can get thicker when you increase the pressure.

Pooh Bear Is A Good Visual Reference For Thinking About Non-Newtonian Fluids

One of the most popular examples of non-Newtonian fluids is the way that honey is more like a liquid when it’s at room temperature, but turns into a solid when it’s cool enough. A great visual comparison for non-Newtonian fluids is the way that Pooh Bear likes his porridge. When Pooh Bear eats his porridge, he wants it to be just the right amount of sticky and smooth. This is a great way to think about non-Newtonian fluids. Imagine that his bowl is a mixture of water and corn starch, which is a common recipe for non-Newtonian fluids. As his spoon presses into the mixture, it gets thicker and more sticky.

They’re Used In Everything From Shaving Cream To Adhesives

Non-Newtonian fluids are used in so many products it’s almost impossible to list them all. You’ve probably noticed them in many of the products below. Shaving Cream: When you apply shaving cream to your face, it stays in a liquid form and doesn’t come off easily. However, after a few minutes, it turns into a solid and is easier to wipe off. Wallpaper Paste: Wallpaper paste is a non-Newtonian fluid, which is why it’s so thick and sticky. After you let it dry, it becomes a hard, non-Newtonian fluid that prevents the wallpaper from peeling. Food Coloring: Food coloring is made from a non-Newtonian fluid that stays in a liquid state at room temperature. Adhesives: While adhesives we make from natural materials like tree sap or tar, synthetic adhesives are non-Newtonian fluids.

They Get Sticky When Pressured

One of the most interesting properties of non-Newtonian fluids is that when pressured, they become sticky. This is because the molecules in non-Newtonian fluids are flexible enough to move around and bump into each other. The more pressure that’s applied, the more they bump into each other and get sticky. The best way to think about this is to imagine bubbles. Bubbles are made of water so they are a Newtonian fluid. So, when a bubble is sitting on the surface of water, it is free to move around, pop and float wherever it wants. Now, when that bubble is underwater, it can’t move around as easily. Pressure has been applied to the bubble and it’s stuck in one place. This is what happens to non-Newtonian fluids when they’re pressured.

They’re Typically Made From Natural Sources

Non-Newtonian fluids are typically made from a variety of natural ingredients. These include starches and proteins, like those found in soybeans, milk, eggs and corn. There are also synthetic non-Newtonian fluids that are made from polymers like polyethylene terephthalate (PET) and polyvinyl alcohol (PVOH), which you may have seen in the ingredients list on some products. Starches and proteins are made from a single molecule, which gives them very specific properties. They are very flexible, which makes them useful for many applications. They are also inexpensive and can be made in large quantities.

In The Kitchen, You’ll Find Them In Baking Mixes And Mayonnaise

Another common use of non-Newtonian fluids is in baking mixes, like pancake and cake mixes, as well as mayonnaise. Cake Mix: When you add water to a cake mix and pour it into the pan, it stays in a liquid state because there isn’t enough pressure to turn it into a solid. However, once the cake is done baking, the heat and steam inside the pan turns the cake mix into a solid, which makes it easier to remove from the pan. Mayonnaise: While the word “mayonnaise” is French for “sauce made from eggs,” American mayonnaise is made from oil, eggs, vinegar, lemon juice, mustard and other spices and flavorings like turmeric. When making mayo, the ingredients are blended together, heated and then they’re cooled. This cooling process changes the non-Newtonian fluid into a non-Newtonian solid that holds the ingredients together.

Final Words: Just Because Something Looks Weird Doesn’t Mean It’s Bad

Newtonian fluids are easy to understand, but non-Newtonian fluids are a bit more complicated. Just know that whenever you see something that looks weird, it is probably a non-Newtonian fluid. The great thing about non-Newtonian fluids is that they can be made from a variety of different sources, like starch and proteins, which makes them even more interesting.

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