How to Make Slime with PVA, Borax, and Water
Introduction: This lab teaches students about cross-linking polymers via hydrogen bonding. It should be given after students have a working knowledge of covalent bonding and polymer chains, but this lab can help reinforce those concepts. Students can see how quickly two relatively free flowing liquids, when mixed together, can form gel they can call “slime.” The students should take diligent notes in their notebooks and come up with possible explanations for the observed response of the liquids when mixed together as well as the physical response of the gel when it is exposed to different strain rates.
Materials: -Polyvinyl alcohol (PVA)
-Borax soap
-Plastic cups
-Food coloring
-Stirring stick
-Measuring cups and spoons
-Zip-lock bag
Preparation:“Slime Goo” kit can be purchased from Steve Spangler Science. If you wish to make them yourself, prepare 4% PVA and Borax solutions with water separately (take care to ensure the PVA and Borax are fully dissolved). Food coloring can be added as needed to the PVA solution for effect of the final slime.
Procedure:-Students pour PVA solution into a zip-lock bag.
-Record observations on the physical state of the liquid (students are encouraged to run liquid in bag over their fingers etc.).
-Students then add a small amount of the Borax solution to the bag.
-Record observations on the physical state of the gel/slime (the more Borax solution the student adds the less liquid like the gel will become).
-Students then write their explanations for the physicalchange of the liquids.
Explain: Most liquids, such as water, are made up of small, unconnected molecules bouncing around and tumbling over and into one another. Unconnected to each other these single molecules can be calledmonomers. Monomer liquids flow easily and are seldom gooey or sticky to the touch. In other substances, the monomers are linked together in identical, repetitive segments that form long chains of molecules known aspolymers. These long chains don’t flow over and across one another very easily. Liquid polymers tend to be gooier and flow more slowly than liquid monomers. The PVA used in this activity is a liquid polymer.
[You might use this analogy to help the kids understand what happened. Picture a box full of tiny, steel chains that slip and slide easily across one another. Each chain is made up of hundreds of individual links but one chain is not connected to another chain. If you reach in and grab one chain and pull it out, that’s what you get: one chain. Suppose you stir a whole bunch of tiny magnets into the box of chains. The magnets randomly connect the chains together in many locations, making a single, large blob of chains. Now if you reach in and grab one chain, you’ll lift out the entire pile]
Adding Borax solution to the PVA does pretty much the same thing (only it’s a chemical, not a magnetic, connection). Borax loves to connect with water and billions of Borax molecules randomly link trillions of water molecules found anywhere on the chains of PVA (Figure 1). Now when you pull out one PVA chain, all the rest come with it in a blob. In the chemical reaction that the kids made, they got a slow-moving, glistening mass that’s known as a hydrogen-bonded, cross-linked polymer gel (slime is way easier to say).
The slime will stretch out if it is pulled slowly and at a steady pace. This is the chains in the gel aligning in the direction the student is pulling. If the slime is yanked quickly the gel will break apart. The hydrogen bonding which crosslinks the gel is not as strong as the covalent bonds of the polymer chain and can be broken apart and reformed. A high strain rate from quickly yanking the gel does not allow the chains to align and the slime to stretch, so the hydrogen bonds break and the slime separates.
Pictures: