The Secrets Behind Slime, from Borax to Biology
- Synthesis Writers
- Apr 27
- 3 min read
Have you ever meticulously mixed different ratios of household materials, hoping they would combine to form the delightful slippery substance we call slime? You may not have realized it in the moment, but you could consider yourself an amateur chemist!
If you successfully created slime as a kid, you were doing more than just contributing to the 2016-era craze; you were forming a non-Newtonian fluid. These fluids don’t follow Isaac’s law of viscosity; their “thickness” changes when a force is applied. You may be familiar with other non-Newtonian fluids, such as ketchup or mixtures of cornstarch and water (“Oobleck”).
Non-Newtonian fluids can be categorized into shear-thinning and shear-thickening fluids. Shear-thinning fluids become less viscous when more force is applied. Think of how paint feels thinner when it’s mixed up. Conversely, shear-thickening fluids become more viscous when more force is applied; slime typically falls into this category.
Slime can be created using a variety of household materials. Broadly, slime is composed of polymers, which are large molecules that have repeated monomer subunits. If one LEGO brick is a monomer, a polymer is the assembled LEGO set.
Polymers can be natural, such as starch, or synthetic, such as polyester or homemade slime. Mixing glue and borax in water is one classic way to assemble the beloved polymer that makes up slime.
Borax (Na2B4O7•10H2O) is a salt that dissolves and reacts with water to form borate ions (B(OH)4-). Polyvinyl alcohol is the chemical that makes up PVA glue like Elmers’ glue. When these two chemicals are mixed together, they form hydrogen bonds: both chemicals have partially positive hydrogen atoms and partially negative oxygen atoms that are attracted to each other.
As its name implies, polyvinyl alcohol is already a polymer, but mixing it with borax creates an even larger cross-linked system. This new polymer acts like a net with water molecules trapped inside, making slime feel wet.
It’s pretty simple to create slime at home, given that you have the necessary materials. But slime isn’t just a man-made phenomenon. It can occur naturally and has a variety of functions.
Take the hagfish. When attacked, this eel-like fish releases mucus and fibrous “slime threads” into the surrounding water to rapidly create a defensive cloud of slime. Despite consisting mostly of water, the ejected protein threads (another example of a polymer) strengthen the slime. This slime can clog predators’ gills and give the fish a chance to escape.
Slimy secretions play an important role in the plant world as well. Mucilage is a mixture primarily made of polysaccharides, which are polymers composed of many linked sugar monomers. It can be secreted by roots, seeds, leaves, and stems, depending on the plant species.
Mucilage can serve a protective function in plants; root mucilage is a slimy coating that reduces friction as a root grows. It can also help roots take up water in drought conditions, as well as feed the beneficial microorganisms that live in the rhizosphere, which is the microenvironment around the roots.
In humans, mucus coats our moist surfaces, such as our eyes, lungs, and stomach. This slimy shield prevents tissues from drying out and hopefully traps pathogens before they can cause illness. When you breathe in bacteria, they typically get trapped in the mucus lining your airways before they are swept away by tiny hairs called cilia.
While you eat, sleep, or play with your DIY slime, your body makes its own slime (with no glue and no borax) to keep you healthy. The sticky and viscous properties that come from slime’s fascinating polymers are crucial, whether that’s in creating the perfect stress-relieving craft or serving as an important line of defense.
By Amelia DeHoff
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