The Properties of Slime {Polymer Play}

This session of polymer play extends yesterday’s session as the children learn about the properties of slime.

Key Properties of Slime

Slime is a non-Newtonian fluid, which means it exhibits properties of both a solid and a liquid depending on the stress applied to it. Its unique texture and behavior come from a chemical process called cross-linking, which creates a polymer network that traps water.

Physical properties

Non-Newtonian behavior: Unlike water, which has a constant viscosity, slime’s viscosity changes with stress.
- Acts like a liquid: When left alone or stretched slowly, the polymer chains slide past one another, allowing the slime to flow and ooze like a thick liquid.
- Acts like a solid: When squeezed, pulled quickly, or hit, the polymer chains become entangled, causing the substance to resist the force and feel like a wet solid. A ball of slime can even bounce.
Viscoelasticity: Slime exhibits both viscous (liquid-like) and elastic (solid-like) properties, which is why it can stretch and deform without breaking when manipulated slowly, but will snap if pulled too quickly.
Flexible and deformable: The substance is highly flexible and can be molded and shaped in many ways.
Texture: Slime has a gooey, slippery, and sometimes sticky or wet-to-the-touch consistency.
Self-healing: If torn into pieces, the separate parts can be pushed back together to reform as a single mass.
Temperature sensitivity: The texture of most slimes is affected by temperature. It tends to become more fluid when warm and firmer when cold.

Chemical Properties

Polymer composition: Standard slime is a polymer-based material. It is created by combining a polymer, typically polyvinyl acetate (PVA) found in white school glue, with an activator.
Cross-linking: The defining chemical property of slime is the cross-linking reaction between the polymer chains and an activator.
- The process: The activator, such as borax, saline solution, or liquid starch, releases borate ions. These ions create temporary hydrogen bonds that act as “bridges” between the long, tangled PVA polymer chains.
- The network: This process transforms the mixture from a free-flowing liquid into a gel-like, three-dimensional network that traps water, giving slime its characteristic consistency.
Adjustable consistency: The ratio of ingredients used significantly impacts the final product.
- Adding more activator creates more cross-links, resulting in a firmer, less stretchy slime.
- Adding less activator results in fewer cross-links and a stretchier, more fluid consistency.
pH sensitivity: The firmness of slime can be affected by pH. Adding an acid can break the hydrogen bonds and make the slime more liquid, while adding a base can restore the firmness.

What Makes Slime Behave This Way?

Slime is made by mixing a polymer, like polyvinyl alcohol (PVA) from white glue, with a borate ion solution (like contact lens solution or borax).
The borate ions create cross-links between the long PVA polymer chains.
When you apply a gentle force, the cross-links have time to shift, allowing the slime to flow.
When you apply a sudden, hard force, the cross-links can’t shift fast enough, and the slime resists and snaps, behaving like a solid.