Transcript Non-Newtonian Fluids

NON-NEWTONIAN
FLUIDS
AND POLYMERS
What are
they?
VOCABULARY
 Non-Newtonian
• does NOT follow the laws of physics as described by Newton
 Dilatant
• adding energy (shear force) makes a liquid thicker or more
rigid – more viscous
• examples – oobleck (cornstarch-water mixture), liquid body
armor
 Thixotropic
• adding energy (shear force) makes a solid thinner or liquefy
–
less viscous
• examples – catsup, concrete, some paint, printer’s ink
 Viscosity
• resistance or opposition to flow of a liquid
NEWTONIAN AND NON-NEWTONIAN
FLUIDS
 Fluids can be categorized as Newtonian and non Newtonian. The viscosity of the Newtonian fluids
remains constant at all shear rates at a constant
temperature and pressure. But, for a non -Newtonian
fluid, the viscosity varies with the shear rate and
time.
 The viscosity for fluid materials can be measured at
different shear rates using a viscometer.
 Shearing is a motion of parallel surfaces sliding past
each other.
GLOP / OOBLECK - DILATNAT
 Glop is made by adding cornstarch with water.
 Glop has many other names such as Oobleck, Gloop, etc.
OOBLECK / GLOP - DETAILS
 A “correctly-made” batch of Glop is a dilatant NonNewtonian Fluid.
 Glop should move like a liquid when slowly stirred. It
will be thick and viscous but still flow. When stirred
quickly (more shear force applied), the mixture
should “lock up” and behave like a solid. Upon sitting
still, the mixture will return to its fluid state.
DINO SNOT / SLIME / GLORAX DILATANT
 Dino Snot is a mixture of borax solution and glue . When Borax
and glue are mixed, the Borax links with the glue (polymers)
to create a slime
 It tends to be a little more viscous than glop, but just as much
fun to play with! Also a dilatant non -Newtonian fluid.
DINO SNOT / GLORAX - DETAILS
 Gloraz is also a dilatant non-Newtonian fluid. You can bounce
it, toss it around, break it. It will “snap” when ripped or bent
quickly but if pulled gently it will stretch slowly and ooze.
QUICK SAND - THIXOTROPIC
 Quick sand is the
opposite of dilatant. It is
thixotropic. The more you
move it around, the more
liquid it becomes.
 Quicksand is basically
just ordinary sand that
has been so saturated
with water that the
friction between sand
particles is reduced. The
resulting sand is a
mushy mixture of sand
and water that can no
longer support any
weight.
SILLY PUTT Y - THIXOTROPIC
 Silly putty is also a thixotropic non -Newtonian fluid. As you
move it, it becomes more fluid.
MORE THIXOTROPIC
 Ketchup, hair gel, some paint and toothpaste are good every
day examples of thixotropic non -Newtonian fluids. Each
retains its shape until force is added and then it flows. Once
force is removed, it “hardens” back to solid -like properties.
Paint stays on the brush but can spread real thin on walls.
MORE THIXOTROPIC – EXAMPLES
 A landslide is an example of a thixotropic event. Clay is very
thixotropic.
 Thixotropy in the Human Body: Synovial fluid in joints and
connective tissue each become more fluid when they are stirred
up, and more solid when they sit without being disturbed .
 Website with videos: http://www.squidoo.com/thixotropy
HOW DO NON-NEWTONIAN FLUIDS
WORK?
The answer lies in POLYMERS.
POLYMERS
 A polymer is a large molecule in which the atoms are
connected in repeating links. Each separate link is a
monomer. "Mono" means one and "poly" means
many. “mer” means part.
NAMING POLYMERS
 If the "units" called monomers in a polymer are all
the same, then the polymer is called a
"homopolymer". Homopolymers are named by adding
the prefix poly- before the monomer name from
which the polymer is made. For example, a polymer
made by bonding styrene monomer molecules
together is called polystyrene.
POLYMERS
 Polymers come naturally, such as in protein molecules, or can
be synthetic, as in rubber, plastic, white glue, money, or a
polyester fabric.
 There are 4 main types of synthetic polymers:




thermoplastics
thermosets
elastomers
synthetic fibers
DILATANT: WHAT IS HAPPENING?
 Cornstarch is a polymer.
 Water and cornstarch do not mix real well. The starch doesn’t
fully dissolve; it is more of a suspension. The starch molecule
“rolls up” from both ends and becomes somewhat of a
spherical shape that might resemble BB’s. When slowly
stirred, the starch “balls” roll around each other and the
mixture has fluid properties.
DILATANT: WHAT IS HAPPENING?
 When a larger amount of shear force is applied, the molecule
uncurls and becomes more linear. These long molecules then
entangle and the mixture becomes rigid like a solid. When the
shear force is removed, the molecules move more freely and
“roll” back up into balls which allows the mixture to flow like
a liquid again.
THIXOTROPIC – WHAT IS HAPPENING?
THIXOTROPIC – WHAT IS HAPPENING?
 Thixotropic materials are non-Newtonian fluids which are gel like at rest, but tend to flow when agitated or stressed. The
particles of this type of product are held together by weak
forces at low shear rates, whereas at high shear rates the
particles tend to separate.
 The shear force causes a disruption in the molecular
structure, weakening it and making it more fluid.
 Sometime the structure is able to return to it’s original state
instantly (like gel or catsup) and these are called
pseudoplastic fluids.
 Other times it stays more fluid (like yogurt, and ice cream).
The end 