What gives slime it’s unique, slimey qualities? Crazy question… but now that we think about it, we’d love to know!
Below you will find a step by step activity for making slime along with fun ways to learn about light, color, viscosity, and pH. This activity was put together by students at the North Carolina School for Science and Math…. for students, by students and from The Science Muse!
What gives slime its unique snotty qualities?
The laugh-trigger for the gross-at-heart enjoys the formal name polyvinyl alcohol (PVA) slime. It is a high viscosity, non-Newtonian fluid with interesting characteristics.
Create PVA slime by mixing a 4% solution of PVA with a solution of sodium borate, known as borax. The molecular bonding of PVA with the borate ions explains the slime-forming process.
Cross-linking occurs when PVA is added to sodium borate; the electronegative oxygen on borate forms weak hydrogen bonds with the hydroxyl groups of PVA. The unique properties of PVA slime are a result of this cross-linking and make slime a useful teaching material. Plus the ingredients are cheap and readily available, PVA slime is nontoxic, and students enjoy snot-like substances.
Create PVA slime in your lab
Materials (small recipe)
Keep the sodium borate solution and PVA solution in a 1:5 volume ratio if you increase or decrease the amount of slime you make. Below is a picture of slime made with this formula. The slime appears green when flat on a sheet of white paper. Slime appears red as white light passes through it. Make slime more “snot-like” by increasing the PVA to sodium borate ratio.
Properties of light
Objects either absorb or reflect incoming light waves. Some light-absorbing substances reemit the light a different color.
In each molecule, electrons vibrate at a natural frequency. When the incoming light-wave frequency exactly matches the natural frequency of an object’s molecules, the light’s energy converts to the electrons’ vibrational energy, which in turn transfers into thermal energy. If all light is reflected, the object appears white. If all light is absorbed, the object appears black.
In slime, fluorescein absorbs the blue-green light and fluoresces to emit green light, while bromphenol blue absorbs every color except red. Thus, when looking at slime from the same side as the light, we only see the slime’s surface fluorescence, which is green. However, when looking from the side opposite the light, the light waves transmitted through the slime also go through the bromphenol blue, where only red light can pass. This shows in spectra below:
What is color?
Use slime to help students investigate what gives objects their color. Students can vary the amount of bromphenol blue to change the slime’s color from purple to red. Or they can use the above formula but substitute another pH indicator for bromphenol blue.
The following data table shows the color of slime left on a black lab table (Fluoresced Color) and viewed in front of a light (Transmitted Color).
|Indicator||Fluoresced Color||Transmitted Color|
If you have a spectroscope, students can investigate the wavelength transmitted and predict the effect on the color of the slime.
Before making slimes, students can analyze the dyes of the slimes to predict which dyes will work best. Have students use a spectrometer to measure the transmittances of the 5 dyes. The graphs should look like this.
Is slime a solid or liquid?
Have students observe and describe the behavior of slime.
A liquid fluid (as opposed to a non-Newtonian fluid) takes the shape of its container and is free-flowing. Different fluids have different resistances when deformed by external forces. This is known as viscosity. For example, water pours more easily than honey; thus, honey is relatively more viscous than water. Slime is a non-Newtonian fluid.
Non-Newtonian fluids such as pudding, cornstarch paste (oobleck), and slime don’t pour easily. When you put pressure on slime it will expand, much like wet sand. Slowly stretched, it will thin and flow, but applying pressure quickly breaks slime.
The pH properties of polyvinyl alcohol slime
The pH of polyvinyl alcohol slime is approximately 9.0. This basic slime contains hydrogen bonds that help maintain firmness and adherence. The addition of an acid such as HCl helps break the hydrogen bonds. If hydrogen bonds help keep the polymer together, how will a loss of hydrogen bonds affect the slime’s physical properties? The following activity helps answer that question.