Organic Chemistry
                                Cross-Linking Polymers

Purpose:      To make “slime” from polyvinyl alcohol and sodium borate decahydrate.

Materials:            4% polyvinyl alcohol solution; 4% sodium borate decahydrate solution, food coloring, cup, stirring rod, graduated cylinder

Safety:    Wear goggles.

Background:   Polyvinyl alcohol is a homopolymer.  The repeating monomer in polyvinyl alcohol contains C2H3OH.  This monomer is attached to another of its kind over and over for any amount of times.  It is soluble in water, but not very.  This is why it is a 4% solution.

Procedure:

  1. Measure 50 mL of the polyvinyl alcohol solution and pour it into the cup.
  2. Add 2 drops of food coloring.
  3. Measure 6 mL of the sodium borate solution.
  4. Add the sodium borate solution to the polyvinyl alcohol solution while stirring. (Stir well.)
  5. Remove the material from the cup and knead it in your hands. The material will become firm and lose some of its stickiness.
  6. Explore and shape the resulting substance. (It is fairly harmless, and you can handle it as long as you wash your hands afterwards. Do not place the slime or your hands in our near your mouth since the sodium borate is toxic when ingested.)
Observations:

            The polyvinyl alcohol had a very oily texture and felt very slippery.  When the food coloring was added to the alcohol, it stayed in a small area and did not mix with the entire solution until it was stirred with the stirring rod.  When the borate was poured into the alcohol, the solution gelled up where it had been poured.  The gel stuck to the stirring rod while the rest of the solution stayed as a liquid.  Once enough borate was added, the entire solution became a gel.  There were lots of tiny air bubbles in the gel.  After molding the gel, it became firmer and less sticky.  When the gel was stretched slowly, it stretched into a very fine piece of material without breaking.  If it was pulled apart quickly, the slime broke apart in a clear line through the middle.  It could be rolled into a ball and when it was gently dropped, it bounced a little bit, but not very high. When it was thrown down with great force, the slime splattered in small crumbles everywhere.



Part II

Purpose:  To observe the effects of sodium chloride on hair gel.

Materials:  Sodium chloride (table salt), Petri dishes, hair gel.

Procedure:

·      Pour hair gel into two Petri dishes

·      Cover one with sodium chloride

·      Stir if necessary

 

 

Observations:

            The hair gel that was poured into the two Petri dishes was light blue/turquoise and almost see-through.  It had tiny air bubbles throughout.  It was between a solid and a liquid, as it did not form to the Petri dish, yet it was still moveable.  When the sodium chloride was added, the gel began to liquefy and run off to the sides of the Petri dish.  When it was stirred, all of the gel liquefied and became a murky, light blue liquid.  The air bubbles went out to the sides of the Petri dish.  While this was happening, it smelled very strongly of the hair gel.

 

                                                                 Overall Discussion

            The high viscosity of the polyvinyl alcohol was due to the size of the molecules and how slowly they moved. The reason that the polyvinyl alcohol gelled up when the sodium borate decahydrate was added is that the borate formed links between all of the polyvinyl alcohol polymer chains.  This stuck them together in a chaotic jumble and restricted their movement.

            The sodium chloride reacted with the links in the polymers of hair gel and broke them up.  This made the molecules only tangled within each other, but not linked in all directions.  With a bit of movement from the molecules, they would untangle and release any air, water or aromas trapped within the gel.  This also let the molecules move much more freely, making it a liquid.