This version of slime science is more detailed and science-focused for those who have more time. You should read the shorter version first to get an overview of things.
Polyvinyl alcohol (PVA) liquid is filled with tangled and twisted strands of polymer. Think of a plate of cooked spaghetti. Simply dumped onto a plate, the pasta forms a tangled pile. When stirred with a finger, however, the pieces tend to line up and to “smooth out” a little. With no bonding agent in the mix, stirring the PVA liquid does the same thing and produces a cool, slippery feeling on your finger.
While “smoothing” the polymer by stirring may straighten the PVA a little, a cross-linking agent – the Activator solution – is needed to produce slime. Cross-linking agents are ions that temporarily connect polymer strands using relatively weak ionic bonds. These bonds – usually hydrogen bonding – are strong enough to link the polymer strands together but not strong enough to make the mass a complete solid. They break easily but reform under flow as well. The fact that PVA is so soluble in water may be due to its extensive hydrogen bonding ability.
PVA slime is a non-Newtonian fluid that is dilatant. In other words, it dilates or expands when a force is applied to it. It earned the non-Newtonian label because it doesn’t follow the rules laid down by Sir Isaac Newton. Obedient fluids maintain a constant “viscosity” depending on their composition. (Viscosity is a measurement of the resistance to flow when a strain is produced in the substance by some externally applied force.) Liquid water is always runny and has a low viscosity. Honey is a thick, slow moving liquid with a high viscosity. (Temperature changes can alter both of these viscosities.) Slime’s viscosity can be changed based on the level of a force applied to it. Other thick liquids that have a variable viscosity include ketchup, gelatin, some glues, corn starch in water, quicksand, wet sand on the beach, some printer’s inks, and Silly Putty. If even a small amount of force is applied to slime, like stirring it with a finger, it’s somewhat watery. If a lot of force is applied suddenly, such as hitting it with your hand, the slime briefly becomes a solid as water is pushed aside by the impact and the molecular matrix resists the force. It’s how molecules are bonded in slime that accounts for the interesting results you see.
While the PVA gives slime its foundation, an Activator solution is needed to move it into the non-Newtonian realm. In most PVA slime mixtures, sodium tetraborate is used as the Activator and is about 2% of the final slime. When dissolved in water, it dissociates into sodium ions and borate ions. These ions mix among the polymer chains and form weak ionic bonds between them and the liquid that results is a thicker material: slime! These bonds allow the PVA to stretch and flow when a force is applied to the slime, be it gravity or a smack. The ratio of the polymer to the Activator solution is a factor in the consistency of the finished slime. You can change slime’s texture simply by using more or less Activator solution.
The most abundant material in slime is water. In fact, water is well over 90% of the slime you’re holding. The remaining chemistry is pretty simple. PVA is a long-chain polymer that has a “backbone” of carbon (C) atoms with numerous hydroxyl (OH) groups connected to it. As a result, only about 2% PVA is needed in the mix. The PVA molecule has a structure that’s made by repeating vinyl alcohol monomers.