The Science Behind Slime

What's Happening?

Elmer's glue is a type of linear polymer called “polyvinyl acetate," which is made of carbon, oxygen and hydrogen. The glue has long flexible molecules in it (polymers.) These polymer molecules slide past each other as a liquid.

When Borax is dissolved in water, it forms an ion called the borate ion (B(OH)4–). When the borax solution is added to the glue solution, the borate ions help link the long polymer molecules to each other so they cannot move and flow as easily.

The polyvinyl acetate polymer cross-links to itself when reacted with borax. Basically, borax acts as a linker to bring together the glue strands into a network. When enough polymer molecules get hooked together in the right way, the glue solution changes from being very liquidy to a rubbery substance that is highly viscous (SLIME!)

The Science Behind Slime

Why does this reaction create a more viscous substance (slime)?

Answer: Cross-linking!!!!

The type of slime we made forms as a result of cross-linking between the protein molecules of the glue and the borate ions (B(OH)4–) of the borax solution. Cross-linking involves the formation of bonds that link together large molecules in such a way that they are no longer free to slide past one another. The large protein molecules in the glue already have trouble moving past each other; the glue has to be squeezed from the bottle. The borate ions link the big molecules to each other, making even bigger molecules, and it becomes even more difficult for them to slide past one another. The result is a tangled mass that is SLIME!

How it Works

Glue contains the polymer polyvinyl alcohol and has the structure:

Borax forms the borate ion when in solution. This ion has the structure:

Sources

The borate ion can make weak bonds with the OH groups in the polymer chains so it can link the chains together as shown below. This is called cross-linking.

https://www.teachengineering.org/activities/view/csu_polymer_lesson01_activity1

http://www.carolina.com/teacher-resources/Interactive/chemistry-activities-with-slime/tr10850.tr

http://sacnasstudentchapter.wp.txstate.edu/welcome-to-sacnas-at-txstate/experiments/

https://www.acs.org/content/acs/en/education/whatischemistry/adventures-in-chemistry/experiments/slime.html

https://www.scientificamerican.com/article/bring-science-home-playing-with-polymers/

Polymers

The cross-linking changes the properties of the polymer from a viscous liquid to a much more viscous slime.

Polymers are long molecules made up of many smaller molecules, or monomers, in a repeating chain.

Polymers are found in a variety of materials that have a broad range of properties. Materials made from polymers can be found in nature, such as amber and natural rubber, or generated synthetically, such as glue, nylon, silicone and all plastics.

Molecular Bonding

Viscosity

ENJOY YOUR SLIME!

Viscosity refers to a fluid's resistance to flow. The more viscous a substance, the slower it flows.

Ex. Ketchup is more difficult to pour than water, because ketchup is more viscous. Peanut butter is more viscous than ketchup.

H4BO4

PVA

Slime

Cross-linking occurs when the polyvinyl alcohol polymer (PVA) from glue is added to sodium borate (Borax); the electronegative oxygen on borate forms weak hydrogen bonds with the hydroxyl groups of PVA.