Polymer Chemistry: Slime, Silly Putty, Instant Worms
[Shopping List: Elmer's Glue; borax powder ; food colors; Solo cups, lids; stir sticks; Sta-Flo liquid starch and/or cornstarch; Worm Goo (sodium alginate dissolved in water), Worm Activator (calcium chloride in water), Atomic Glow, Glow Powder and/or Pearl Swirl chemicals (Steve Spangler), squirt bottles, spoons]
Slime (aka Goblin Boogers, Snot, Gak, etc.):
- Prepare a mixture of 3:1 non-toxic white school glue to water. Add food color for visual appeal.
- Prepare a saturated solution of borax in water. You know it is saturated when no more borax will dissolve, so it remains at the bottom of the container. Pour into smaller bottles or bowls for use.
- Pour about 1 fluid oz. of the glue/water mixture into a 2oz. portion cup.
- Have the child stir the mixture with a popsicle stick as you slowly add drops of borax solution. The mixture should form a glob!
For more of a Silly Putty consistency use liquid starch instead of borax solution, or add a little cornstarch to the borax solution. Any of the Steve Spangler chemicals can be added for additional effects.
Instant Worms
- Pour pre-mixed Worm Activator solution (with food coloring added) into a cup or bowl.
- Squirt "Worm Goo" into the cup. Worms form instantly, but the longer they remain in the activator solution the firmer they will be.
For fluorescent worms add a little Atomic Glow solution (or other fluorescent die) to the worm goo; for glow in the dark worms, add a little Glow Powder; or for metallic worms add some Pearl Swirl. Give kids a lid for their mixing cups (or Ziploc bags) to take polymers home. Put a little of the calcium water in the cup to keep worms from drying out (at home they can allow them to dry out and watch them shrivel up, and if they're lucky, they may be able re-hydrate them).
What's Happening: Polyvinyl acetate (PVA) is a long-chain polymer and is the active ingredient in Elmer’s glue. The B-OH of borax reacts with the acetate group on the PVA, eliminating acetic acid. This reaction serves to cross-link the PVA chains via a borax bridge. The cross-linked molecules glom together and produce the putty-like substance. Explain it to kids like spaghetti: Think of a pot of freshly cooked spaghetti as the glue, with a punch of long molecules that can easily slide past one another. As the water dries from the spaghetti, however, the long strands stick together (via cross linking) forming a solid mass.
The worms also illustrate a cross-linking reaction. Sodium alginate comes from seaweed (algae), and is also a very long chain polymer. When it contacts calcium ions in the water it instantly cross-links to form a solid (actually a gel) skin layer, but the skin slows down diffusion of calcium, so the inside of the worm remains liquid alginate goo for much longer. Gently squeeze a worm and you should feel the liquid inside. You may even see some air bubbles moving around. As the worm soaks in the solution calcium will slowly diffuse through the skin and eventually the entire worm will be solid (about 10-20 minutes for a typical worm).
All of these experiments provide a good opportunity to talk about the differences between solids and liquids. Which are these?
Variations: Try making little balls and tadpoles in addition to the worms by varying your squirting technique. Another trick is to make a large ball or blob by squirting a little goo directly into a Solo cup, then adding 2 or 3 teaspoons of calcium water and swirling the solution several times in the cup before gently pouring it into the big bowl of calcium water. Again a skin forms which slows down calcium diffusion to the inside of the blob, so it will be very fragile for several minutes, and requires a couple of hours to completely solidify. Don't squeeze too hard or the blob will pop and squirt goo everywhere.
|
