Make Rheopectic slime in less than 15 minutes! (It is not Oobleck)

Step 7 Differences with other non-Newtonian fluids (Oobleck vs Slime )

Is this slime the same as Oobleck? The answer is NO.

Oobleck and this slime are quite different. Both are non-Newtonian fluids that share some properties but not all. The chemical and structural reasons for their behavior are different.

Here are the differences:

First:
Oobleck is a simple colloidal dispersion of starch in water.
Slime is a cross-linked polymer made from another polymer, polyvinyl acetate.

Second:
Starch is a polysaccharide, a natural polymer present in plants.
Polyvinyl acetate is obtained by chemical synthesis. It is a synthetic polymer.

Third:
You can explain the properties of slime by referring to its chemical structure. (refer to step 6)

However, Oobleck is only a physical dispersion, so there is not chemical reactions involved. I think its odd properties are due to a physical phenomenon called adsorption. (NOTE: This is not the same as "absorption." See the glossary in the next step.)

I'll try to explain how I reached this conclusion:
I read a lot of things about Oobleck on the net. 99% of the sites focus on its non-Newtonian properties but no one tries to explain the phenomena that produce it. I found this link (which is in Spanish; sorry) which tried to explain the origins of Oobleck's behavior, but none of these theories satisfied me. So I formulated my own theory:

First I'll explain something about starch and its properties at different temperatures. Commercial native starch is formed by grains which have a low humidity. Starch is not soluble in cold water, it only disperses and adsorbs a few water molecules. With water at room temperature, starch grains can absorb a little water, but it is really a minimal amount. To make starch grains absorb water, you need to heat the water to at least 70 degrees C (158 degrees F). When the starch grains start to absorb water they swell; you get a clear and viscous starch solution at this point. At higher temperatures (90 C/194 F), the starch grains finally break and at 95 C/203 F they form a solution. When this solution is cooled the solution becomes very viscous until it forms a soft gel.

Knowing that, my conclusion is that at room temperature the predominant phenomena between water and starch grains is adsorption. So the Oobleck behavior is due to adsorption. I think when Oobleck is fluid, the starch grains and water have a normal adsorption rate and the space between starch grains is bigger. But when you apply a shear force on it, the starch grains are forced to adsorb more water. The higher the shear force, the more the starch grains adsorb water. Because it is a really saturated dispersion and the grains are spherical there is a large amount of surface area for the water to be adsorbed onto. Most of the water is adsorbed; the grains pack together; and Oobleck becomes solid like a rock. But this kind of adsorption is highly unstable so when the shear force is stopped, the starch grains automatically expulse the adsorbed water and in a matter of seconds the Oobleck becomes liquid again. The more you play with Oobleck the more viscous it becomes, but it is still liquid. I think this happens because of the slight water absorption that occurs at this temperature. You are heating the Oobleck with your hands, so you are helping the grains to absorb water a little bit; the water binds to the starch grains, thus the solution becomes more viscous.

Fourth:
For practical applications there are other differences:
Making Oobleck is a really dirty activity, because it tends to leave everything that it touches covered with a thin white layer of dried starch.
Slime is less dirty and when it is done is not sticky any more. You can pour it on the table, your skin, your clothes, your toys, etc., and you can remove it easily.

Oobleck is starch. If a kid tries to eat it, is less dangerous than if a kid tries to eat slime.

I tried and tried and tried, but my Oobleck never bounced, if you make a thick slime ball it can bounce.

Oobleck's solid form only lasts a few seconds. Slime flows slowly so you can use your creativity to use it for Halloween decoration, for example.

Oobleck is opaque. Slime is very shiny.

You cannot change Oobleck's texture. You can control the slime's synthesis and make it thicker or thinner if you want.

Using the correct shear force, Oobleck can become as hard as a rock. You cannot do this with slime.

Oobleck's shelf life is shorter than slime's because it is more susceptible to microorganism attacks. If you keep your slime well protected from air, its shelf life is longer.

In my opinion both fluids have interesting properties. You should try both of them.

I took the starch images from thissiteCheck it out if you are interested in learning about starch