2. Tina Michetti tinamichetti@hotmail.com SLIME INSTITUT DON BOSCO Avenue du Val d’Or, 90 d 1150 Bruxelles

3. Subject area : Chemistry Age of the students : 12 to 14 Content involved :Chemical bonding, non-Newtonian fluids, polymers, Student skills involved :-Experimental work -Capacity to observe -Capacity to work as a group -Communication skills. Aims :- Develop experimental skills to arouse interest in sciences. -Introduce students to the concepts of chimical bonding, non Newtonian fluids and polymers Turn this ever popular science activity into a real learning experience that is filled with real fun.

5. SLIME is a non-Newtonian fluid, easily made from polyvinyl alcohol and borax, that flows under low stresses but breaks under higher stresses and pressures. This combination of fluid-like and solid-like properties makes it a Maxwell solid. Its behaviour can also be described as being viscoplastic or gelatinous

7.  Tétraborate de sodium décahydraté Na 2 B 4 O 7.10H 2 O  Polyvinylalcool, PVA (MM 88000 n°CAS 9002-89-5 Acros + Eklyps)  Food coloring  Distilled water  1 beaker - 250 ml  1 beaker – 20 ml  Glass stirrer  Magnetic stirrer/hot plate SOLUTIONS  Borax solution 4% Tétraborate de sodium décahydraté Na 2 B 4 O 7.10H 2 O Dissolve 40 g of borax in warm distilled water. Allow to cool, complete to 1l and transfer to a labeled storage bottle  PVA solution 4% : Polyvinylalcool, PVA (MM 88000 n°CAS 9002-89-5 Acros + Eklyps)  Dissolve 40 g PVA in 900 ml hot distilled water (about 80°C), allow to cool and complete the volume to 1 l with water.  The PVA is difficult to dissolve. Use a magnetic stirrer/hot plate, you can simply heat the water to about 90 o C, start the stir bar, and sprinkle in the powder  Ladle the solution into a labeled storage bottle for later use

8. Put 10 ml of borax solution in the 20 ml beaker - add a few drops of food coloring Put 100 ml of PVA solution in the 250 ml beaker Pour the Borax solution into the PVA solution and stir well. Watch the slime form! The polymer you made should be kept in a sealed plastic bag when you aren't playing with it. Also, be sure to keep it away from young kids or pets who might think it's food. Have fun!

10. Slime is a great hands-on lesson in non-Newtonian solids and liquids and the physics of them. In addition, students will gain valuable knowledge about polymers and their formation.

11. How does it work? Two clear liquids are combined and stirred. Within seconds, a gelatinous blob forms, and coalesces on the stirring stick. After a few minutes, the entire liquid has turned to... SLIME!

12. Now for the SCIENCE part.... This POLYMER is unique because it has qualities of both a solid and a liquid: -like a solid you can hold it in your hand and pick it up. -like a liquid does it can take the shape of its containers As you might know, solid molecules are tight together, liquid molecules spread out and break apart (drops). POLYMER molecules CHAIN themselves together (they can stretch and bend like chains) and that makes them special. Jell-O, rubber bands, plastic soda bottles, sneaker soles, even gum are all forms of polymers. and …..for older students

13. Cross-Linking PolyVinyl Alcohol So we start with the single Vinyl Alcohol molecule (called an alcohol by the addition of the hydroxyl group OH- to the vinyl group CH 2 -CH) and string a bunch of them together to form Poly Vinyl Alcohol. Now we have some polymer ready for cross-linking. Our objective will be to add something that will bind several of these long molecules together side-by-side, something like the rungs of a ladder. We start by dissolving some Borax (Na 2 B 4 O 7.10H 2 O) in water, which dissociates into sodium ions and tetraborate ions. The tetraborate ion reacts with water (hydrolyzes) to produce boric acid and the OH - ion. B 4 O 7 -2 (aq) + 7 H 2 O 4 H 3 BO 3 (aq) + 2 OH - (aq) Reaction mechanisms The formation of a gel may be due to hydrogen bonding between boric acid hydroxyl groups and the alcohol groups in polyvinyl alcohol. Hydrogen bonding, as opposed to covalent bonding, would account for the physical properties of the gel. Cross-links in synthetic polymer chemistry When polymer chains are linked together by cross-links, they lose some of their ability to move as individual polymer chains. For example, a liquid polymer (where the chains are freely flowing) can be turned into a "solid" or "gel" by cross-linking the chains together. Cross-links are bonds that link one polymer chain to another. They can be covalent bonds or ionic bonds.

14. The boric acid further reacts with water to form the borate anion. H 3 BO 3 (aq) + 2 H 2 O B(OH) 4 - (aq) + H 3 O + (aq) So now we have the form of the borate ion that we need.,. Hydrogen bonds form between the borate ion and the OH groups on the sides of the Poly Vinyl Alcohol. These bonds are not very strong, and are broken and reformed easily, allowing the slime to sag and move slowly under stress. Let's study this scrambled mess. The green borate ion is in the middle, the PVA chains are on the outside and are bent and twisted, water molecules are dispersed randomly throughout the assembly and dotted blue lines (hydrogen bonds) make connections between Oxygen and Hydrogen, especially to those Oxygen and Hydrogen that are paired up and sticking out the sides of the PVA chains. There are some important features in this picture: a) the polymer chains distort to allow these hydrogen bonds to occur, and b) water molecules dispersed throughout the mess add to the hydrogen bonding. Notice that this picture describes the bonding as if a water molecule had simply been removed from each bond site. This treats the bond as a covalent bond, and not the weaker hydrogen bond which we believe is responsible for the true nature of the relatively weak cross-linking

15. The students can take their slime home in the sealed cup. They should be told that the slime will keep for weeks in the refrigerator, but may become moldy after a week or so if left out. The slime will wash out of most clothing with detergent and warm water.