Sistem non-Newton
Non-Newtonian bodies adalah zat-zat yang tidak mengikuti persamaan
aliran Newton; dispersi heterogen cairan dan padatan seperti larutan
koloid, emulsi, suspensi cair, salep dan produk-produk serupa. Jika bahanbahan non-Newton dianalisis dalam suatu viscometer putar dan hasilnya
diplot, diperoleh berbagai kurva konsistensi yang menggambarkan adanya
tiga kelas aliran yakni; plastis, pseudoplastis, dan dilatan.
Aliran Plastis
kurva aliran plastis tidak melalui titik (0,0) tapi memotong sumbu shearing
stress (atau akan memotong, jika bagian lurus dari kurva tersebut
diekstrapolasikan ke sumbu) pada suatu titik tertentu yang dikenal dengan
harga yield. Bingham bodies tidak akan mengalir sampai shearing stress
dicapai sebesar yield value tersebut. Pada harga stress di bawah harga
yield value, zat bertindak seperti bahan elastic. Ahli rheologi
menggolongkan Bingham bodie sebagai suatu bahan yang
mempunyai/memperlihatkan yield value, seperti halnya zat padat. Sedang
zat-zat yang mulai mengalir pada shearing stress terkecil didefinisikan
sebagai cairan. Yield value adalah suatu sifat yang penting dari dispersedispersi tertentu. Aliran plastis berhubungan dengan adanya partikelpartikel yang terflokulasi dalam suspense pekat. Akibatnya, terbentuk
struktur kontinu di seluruh sistem. Adanya yield value disebabkan oleh
adanya kontak antara partikel-partikel yang berdekatan (disebabbkan oleh
gaya van der waals), yang harus dipecah sebelum aliran dapat terjadi.
Akibatnya yield value merupakan indikasi dari kekuatan flokulasi. Makin
banyak suspense yang terflokulasi, makin tinggi yield valuenya.
Aliran Pseudoplastis
Aliran pseudoplastis diperlihatkan oleh polimer-polimer dalam larutan,
yang merupakan kebalikan dari sistem plastis, yang tersusun dari partikelpartikel yang terflokulasi dalam suspensi. Sejumlah besar produk farmasi
termasuk gom dan sintesis, misalnya: disperse cairan dari tragacanth,
natrium alginate, metilselulosa dan natrium karboksimetil selulosa,
menunjukkan aliran pseudoplastis.
Viskositas zat pseudoplastis berkurang dengan meningkatnya rate of
shear. Viskositas nyata dapat diperoleh pada setiap haraga rate of shear
dari kemiringan tangen (garis singgung) pada kurva pada tittik tertentu.
Aliran Dilatan
Suspense-suspensi tertentu dengan persentase zat padat terdispers yang
tinggi menunjukkan peningkatan dalam daya hambat untuk mengalir dengan
meningkatnya rate of shear. Aliran dilatan adalah kebalikan dari aliran
pseudoplastis. Bahan-bahan aliran dilatan dikenal dengan istilah shearthickening system.
Zat-zat yang mempunyai sifat-sifat aliran dilatan adalah suspensesuspensi yang berkonsentrasi tinggi (kira-kira 50% atau lebih) dari
partikel-partikel kecil yang mengalami deflokulasi .
Diposkan oleh Afra Chemistry Lover di 03.46
http://afrachemistrylover.blogspot.com/2010/02/viskositas.html
2011-02-15
http://web2.clarkson.edu/projects/subramanian/ch301/notes/nonnewto
nian.pdf
2011-02-21
Non-Newtonian fluid
From Wikipedia, the free encyclopedia
This article needs
additional citations for verification.
Please help improve this article by adding reliable
references. Unsourced material may
be challenged and removed. (June 2010)
Continuum mechanics
[show]Laws
[show]Solid mechanics
[hide]Fluid mechanics
Fluids
Fluid statics · Fluid
dynamics
Surface tension
Navier–Stokes equations
Viscosity:
Newtonian, Non-Newtonian
[show]Rheology
[show]Scientists
v·d·e
A non-Newtonian fluid is a fluid whose flow properties differ in any way
from those of Newtonian fluids. Most commonly the viscosity of nonNewtonian fluids is not independent of shear rate or shear rate history.
However, there are some non-Newtonian fluids with shear-independent
viscosity, that nonetheless exhibit normal stress-differences or other
non-Newtonian behavior. Many salt solutions and molten polymers are nonNewtonian fluids, as are many commonly found substances such
as ketchup, custard, toothpaste, starch suspensions, paint, blood,
and shampoo. In a Newtonian fluid, the relation between the shear
stress and the shear rate is linear, passing through the origin, the
constant of proportionality being the coefficient of viscosity. In a nonNewtonian fluid, the relation between the shear stress and the shear
rate is different, and can even be time-dependent. Therefore a constant
coefficient of viscosity cannot be defined.
Although the concept of viscosity is commonly used to characterize a
material, it can be inadequate to describe the mechanical behavior of a
substance, particularly non-Newtonian fluids. They are best studied
through several other rheological properties which relate the relations
between the stress and strain rate tensors under many different flow
conditions, such as oscillatory shear, or extensional flow which are
measured using different devices or rheometers. The properties are
better studied using tensor-valued constitutive equations, which are
common in the field of continuum mechanics.
Contents
[hide]

1 Types of non-Newtonian
behavior
o
1.1 Summary
o
1.2 Shear thickening fluids
o
1.3 Shear thinning fluid
o
1.4 Bingham plastic
o
1.5 Rheopectic
2 Examples

o
2.1 Oobleck
o
2.2 Flubber
o
2.3 Chilled caramel topping
o
2.4 Silly Putty
o
2.5 Ketchup

3 See also

4 References

5 External links
[edit]Types of non-Newtonian behavior
[edit]Summary
Comparison of non-Newtonian, Newtonian, and viscoelastic properties
Viscoelas
Kelvin material
tic
"Parallel" linear
combination of elastic
and viscous effects
Timedependen
t
viscosity
Anelastic
Material returns to a
well-defined "rest
shape"
Rheopectic
Apparent viscosity incr
Some lubricants, wh
eases with duration of
ipped cream
stress[1]
Thixotropic
Some Clays,
Some Drilling Mud,
Apparent viscosity dec many paints, synovi
reases with duration
al fluid,cerebral
[2]
of stress
spinal
fluid, Honey under
certain conditions
Shear
Apparent viscosity incr Suspensions of corn
thickening(dilatan eases with increased
starch or sand in
[3]
t)
stress
water
Timeindepend
ent
Paper pulp in water,
Apparent viscosity dec
viscosity Shear
latex
thinning(pseudopl reases with increased
paint, ice, blood,
astic)
stress[4][5]
syrup, molasses
Generalized Newtonian
fluids
Viscosity is constant
Stress depends on
normal and shear
strain rates and also
the pressure applied
on it
Blood
plasma, Custard
[edit]Shear thickening fluids
Shear thickening fluids are also used in all wheel drive systems utilising
a viscous coupling unit for power transmission.
[edit]Shear thinning fluid
A familiar example of the opposite, a shear thinning fluid, or
pseudoplastic fluid, is paint: one wants the paint to flow readily off the
brush when it is being applied to the surface being painted, but not to
drip excessively.
[edit]Bingham plastic
There are fluids which have a linear shear stress/shear strain
relationship which require a finite yield stress before they begin to flow
(the plot of shear stress against shear strain does not pass through the
origin). These fluids are called Bingham plastics. Several examples are
clay suspensions, drilling mud, toothpaste, mayonnaise, chocolate, and
mustard.
[edit]Rheopectic
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 rheopectic. An opposite case of this, is a fluid
that thins out with time and requires a decreasing stress to maintain a
constant strain rate (thixotropic).
[edit]Examples
[edit]Oobleck
Oobleck on a subwoofer. Applying force to oobleck, by sound waves in this
case, makes the non-Newtonian fluid thicken.[6]
An inexpensive, non-toxic example of a non-Newtonian fluid is a
suspension of starch (e.g. cornflour) in water, sometimes called "oobleck"
or "ooze" (2 parts corn starch to 1 part water).[7][8] Uncooked imitation
custard, being a suspension of primarily cornflour, has the same
properties. The name "oobleck" is derived from the children's
book Bartholomew and the Oobleck.
[edit]Flubber
Main article: Flubber (material)
Flubber is a non-Newtonian fluid, easily made from polyvinyl
alcohol based glues and borax, that flows under low stresses, but breaks
under higher stresses and pressures. This combination of fluid-like and
solid-like properties makes it a Maxwell solid. Its behavior can also be
described as being viscoplastic orgelatinous.[9]
[edit]Chilled caramel topping
Another example of this is chilled caramel ice cream topping. The sudden
application of force—for example by stabbing the surface with a finger,
or rapidly inverting the container holding it—leads to the fluid behaving
like a solid rather than a liquid. This is the "shear thickening" property of
this non-Newtonian fluid. More gentle treatment, such as slowly inserting
a spoon, will leave it in its liquid state. Trying to jerk the spoon back out
again, however, will trigger the return of the temporary solid state. A
person moving quickly and applying sufficient force with their feet can
literally walk across such a liquid.
[edit]Silly Putty
Main article: Silly Putty
Silly Putty is a silicone polymer based suspension which will flow, bounce,
or break depending on strain rate.
[edit]Ketchup
Ketchup is a shear thinning fluid.[3] Shear thinning means that the fluid
viscosity decreases over time given a constant shear. In other words,
fluid motion is initially difficult to start, but once flowing will continue to
do so freely.
[edit]See also

Bingham plastic

Complex fluid

Dissipative particle dynamics

Newtonian fluid

Herschel–Bulkley fluid

Navier–Stokes equations

Pseudoplastic

Dilatant

Quicksand

Rheology

Superfluids
[edit]References
1. ^ Springer handbook of experimental fluid mechanics, Cameron
Tropea, Alexander L. Yarin, John F. Foss, Publisher: Springer, 9
October 2007, ISBN 3540251413, ISBN 978-3540251415,
p.676,Google books
2. ^ Springer handbook of experimental fluid mechanics, Cameron
Tropea, Alexander L. Yarin, John F. Foss, Publisher: Springer, 9
October 2007, ISBN 3540251413, ISBN 978-3540251415,
p.661,Google books
3. ^ a b Pump Application Desk Book, 3rd edition, Paul N. Garay,
Prentice Hall, August 1996, ISBN 0881732311, ISBN 9780881732313, p.358, Google books
4. ^ Rheology of Fluid and Semisolid Foods: Principles and
Applications, M. A. Rao, Publisher: Springer, 2nd edition, 28 August
2007, ISBN 0387709290, ISBN 978-0387709291, p.8, Google
books
5. ^ Emulsions, Foams, and Suspensions: Fundamentals and
Applications, Laurier L. Schramm, Publisher: Wiley VCH, 26 July
2005, ISBN 3527307435, ISBN 978-3527307432p.173, Google
books
6. ^ This demonstration of oobleck is a popular subject for YouTube
videos, such as this.
7. ^ Oobleck: The Dr. Seuss Science Experiment
8. ^ Outrageous Ooze
9. ^ Glurch Meets Oobleck. Iowa State University Extension.
http://en.wikipedia.org/wiki/Non-Newtonian_fluid
2011-02-21