Non-Newtonian fluid
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A non-Newtonian fluid is a
Most commonly, the
Although the concept of viscosity is commonly used in
Types of non-Newtonian behavior
Summary
Viscoelastic
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Kelvin material, Maxwell material
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"Parallel" linear combination of elastic and viscous effects[2] | Some lubricants, whipped cream, Silly Putty |
Time-dependent viscosity | Rheopectic | Apparent viscosity increases with duration of stress | printer ink, gypsum paste
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Thixotropic | Apparent viscosity decreases with duration of stress[2] | floc suspensions, many colloidal suspensions
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Non-Newtonian Viscosity | Shear thickening (dilatant)
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Apparent viscosity increases with increased stress[3] | Suspensions of corn starch in water (oobleck) |
Shear thinning (pseudoplastic) | Apparent viscosity decreases with increased stress[4][5] | ||
Generalized Newtonian fluids | Viscosity is function of the shear strain rate. Stress depends on normal and shear strain rates and also the pressure applied on it |
Blood plasma, custard, water |
Shear thickening fluid
The viscosity of a shear thickening – i.e. dilatant – fluid appears to increase when the shear rate increases. Corn starch suspended in water ("oobleck", see below) is a common example: when stirred slowly it looks milky, when stirred vigorously it feels like a very viscous liquid.
Shear thinning fluid
A familiar example of the opposite, a shear thinning fluid, or pseudoplastic fluid, is wall paint: The paint should flow readily off the brush when it is being applied to a surface but not drip excessively. Note that all thixotropic fluids are extremely shear thinning, but they are significantly time dependent, whereas the colloidal "shear thinning" fluids respond instantaneously to changes in shear rate. Thus, to avoid confusion, the latter classification is more clearly termed pseudoplastic.
Another example of a shear thinning fluid is blood. This application is highly favoured within the body, as it allows the viscosity of blood to decrease with increased shear strain rate.
Bingham plastic
Fluids that have a linear shear stress/shear strain relationship but require a finite yield stress before they begin to flow (the plot of shear stress against shear strain does not pass through the origin) are called Bingham plastics. Several examples are clay suspensions, drilling mud, toothpaste, mayonnaise, chocolate, and mustard. The surface of a Bingham plastic can hold peaks when it is still. By contrast Newtonian fluids have flat featureless surfaces when still.
Rheopectic or anti-thixotropic
There are also fluids whose strain rate is a function of time. Fluids that require a gradually increasing shear stress to maintain a constant strain rate are referred to as
Examples
Many common substances exhibit non-Newtonian flows. These include:[6]
- Soap solutions, cosmetics, and toothpaste
- Food such as
- Natural substances such as magma, lava, gums, honey, and extracts such as vanilla extract
- Biological fluids such as blood, saliva, semen, mucus, and synovial fluid
- Slurries such as cement slurry and paper pulp, emulsions such as mayonnaise, and some kinds of dispersions
Oobleck
An inexpensive, non-toxic example of a non-Newtonian fluid is a suspension of starch (e.g., cornstarch/cornflour) in water, sometimes called "oobleck", "ooze", or "magic mud" (1 part of water to 1.5–2 parts of corn starch).[8][9][10] The name "oobleck" is derived from the Dr. Seuss book Bartholomew and the Oobleck.[8]
Because of its dilatant properties, oobleck is often used in demonstrations that exhibit its unusual behavior. A person may walk on a large tub of oobleck without sinking due to its shear thickening properties, as long as the individual moves quickly enough to provide enough force with each step to cause the thickening. Also, if oobleck is placed on a large subwoofer driven at a sufficiently high volume, it will thicken and form standing waves in response to low frequency sound waves from the speaker. If a person were to punch or hit oobleck, it would thicken and act like a solid. After the blow, the oobleck will go back to its thin liquid-like state.
Flubber (slime)
Flubber, also commonly known as slime, is a non-Newtonian fluid, easily made from
Chilled caramel topping
Another example of non-Newtonian fluid flow is chilled caramel
Silly Putty
Silly Putty is a silicone polymer based suspension that will flow, bounce, or break, depending on strain rate.
Plant resin
Plant resin is a
. When left in a container, it will flow slowly as a liquid to conform to the contours of its container. If struck with greater force, however, it will shatter as a solid.Quicksand
Quicksand is a shear thinning non-Newtonian colloid that gains viscosity at rest. Quicksand's non-Newtonian properties can be observed when it experiences a slight shock (for example, when someone walks on it or agitates it with a stick), shifting between its Gel and Sol phase and seemingly liquefying, causing objects on the surface of the quicksand to sink.
Ketchup
Ketchup is a shear thinning fluid.[3][13] Shear thinning means that the fluid viscosity decreases with increasing shear stress. In other words, fluid motion is initially difficult at slow rates of deformation, but will flow more freely at high rates. Shaking an inverted bottle of ketchup can cause it to transition to a lower viscosity through shear thinning, making it easier to pour from the bottle.
Dry granular flows
Under certain circumstances, flows of granular materials can be modelled as a continuum, for example using the μ(I) rheology. Such continuum models tend to be non-Newtonian, since the apparent viscosity of granular flows increases with pressure and decreases with shear rate. The main difference is the shearing stress and rate of shear.
See also
References
- ^ Ouellette, Jennifer (2013). "An-Ti-Ci-Pa-Tion: The Physics of Dripping Honey". Scientific American.
- ^ ISBN 978-3-540-25141-5.
- ^ ISBN 978-0-88173-231-3.
- ISBN 978-0-387-70929-1.
- ISBN 978-3-527-30743-2.
- ISBN 978-1-4200-1538-6.
- which?]
- ^ a b "Oobleck: The Dr. Seuss Science Experiment". instructables.com.
- ^ "Outrageous Ooze". Exploratorium.
- ISBN 978-0-609-80109-3.
- ^ Glurch Meets Oobleck Archived 6 July 2010 at the Wayback Machine. Iowa State University Extension.
- ^ Barra, Giuseppina (2004). The Rheology of Caramel (PhD). University of Nottingham.
- ^ Cartwright, Jon (2 September 2011). "Microscopy reveals why ketchup squirts". Chemistry World. Royal Society of Chemistry.
External links
- Classical experiments with Non-Newtonian fluids by the National Committee for Fluid Mechanics on YouTube