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 Non-Newtonian 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. If something is slowly pushed down through the mixture, little resistance will be felt and the item will reach the bottom of the cup. If something is quickly rammed onto the surface of the mixture it will not be able to penetrate into the mixture which has become rigid due to the added energy (force).

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 Putty - 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).

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