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Non-Newtonian Fluids and Their Properties

Anamika Kumari Apr 17, 2019
Named after the famous physicist and mathematician, Sir Isaac Newton, non-Newtonian fluids do not follow his observations made in his work classified as the Newtonian mechanics. Here's some information on these fluids, their properties and applications.

The Mystery of Quicksand

Quicksand is an example of non-Newtonian fluid, whose viscosity increases with the decrease in rate of stress being applied and vice-versa. This is why it obstructs the rapid panicky movements of any object or body inside it. The trick to get out of quicksand is to move slowly towards a safe edge.
Science is amazing and magical. The more we try to understand it, the more complicated it gets. All its complexities are a virtual gift to mankind, prompting man to push his limits to explore further into the darkness. One of such amazing occurrences are the non-Newtonian fluids.

What is a Non-Newtonian Fluid?

To understand the concept of non-Newtonian fluids it is very important to have a clear understanding of the Newtonian fluids in the first place.
According to Newton's theory, under normal temperature and pressure, fluids possess constant flow or viscosity and take the shape of the container in which they are poured. The fluids that satisfy both these conditions are known as 'Newtonian fluids'.
On the contrary, further study in the field of fluid mechanics revealed that there are certain non-homogenous fluids that exhibit a change in their state or a change in viscosity upon the application of shear stress. These fluids are categorized as non-Newtonian fluids.

Properties

The Power Law Equation for fluids give us the relationship between the viscosity, η, and the shear rate, γ.
Mathematically,

η = K γn-1

where, K = flow consistency index (of the material)
n = flow behavior index


The properties of fluids are defined by the flow behavior index, n. If,
n < 1 for Pseudoplastics
n = 1 Newtonian fluid
n > 1 for Dilatants

Thixotropy

Thixotropic plastics are the fluids that experience a decrease in their viscosity with respect to the time for which shear stress was being applied on them.

Rheopecty

Dilatant materials are those whose shear stress depends solely on the time of its application. Viscosity in dilatants increases with the increase in time duration for which the shear stress was maintained upon the fluid. This behavior in fluids is termed rheopecty.

Shear thinning

One of the properties of some non-Newtonian fluids is shear thinning.
Such fluids, under the application of rapidly increasing stress become scarce in consistency due to the slipping of fluid particles over each other.

Shear thickening

Contrary to the shear thinning behavior exhibited by some non-Newtonian fluids, there are quite a few fluids that tend to behave like solids due to the large size of its constituting particles under swift stress. While slow and delayed movement helps the particles to flow.

Bingham plastics

Bingham plastics are those materials that have a linear shear stress vs shear rate characteristics.
These have to overcome a threshold value of shear stress before they begin to flow. As long as the shear stress being applied lies below the threshold value for that material, it retains its original solid state.

Examples of Non-Newtonian Fluids

✤ Cement or paper slurry

✤ Ketchup

✤ Honey

✤ Nail polish

✤ Gelatin

Some Other Examples

✤ Oobleck

✤ Plant resin

✤ Paints

✤ Blood

✤ Whipped cream

Applications

The non-Newtonian fluids have opened up yet another world in the field of material science and its applications, awaiting us with technological surprises. There are plenty of natural events that prove how useful non-Newtonian fluids have been to mankind.
Inspired by these, research scholars have ventured forward to explore the applications of non-Newtonian fluids in our lives. Besides, it has helped science explain some of the disasters and hazardous phenomenon of nature and find ways to combat the same.
Some of these applications include:

✤ To provide a flexible foundation to the built structures in earthquake prone areas to reduce the impact of the vibrations on the construction during an earthquake.
✤ To develop a bodysuit flexible enough to allow body movements but protect the wearer from the swift physical impact of weapons.
✤ Use for recreational and educational purposes.
So, the next time you see a person walking rapidly on a fluid without getting drowned, or hitting a cornstarch mixture with all his might but not penetrating it, you know that it's not magic. Science is what you are dealing with!