Viscous Goo Challenge
Notes
This simple experiment is fun for everyone and is often used as “entertainment”
in science clubs, Open Days or end of year activities. However in this format it
is used as a science investigation by linking observation to numerical values.
This is not intended to be a thorough piece of investigative work, but is used to
illustrate scientific principles in an entertaining way. There are several levels at
which this can be approached depending on the ability of the class that will
carry out the investigation.
Very young / low ability: This can be simply a bit of fun tied in with data
collection
More able KS3 / KS4: The experiment can be used to reinforce ideas about…
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Solid, liquids and gases and their basic properties
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Polymers, their properties and cross linking
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Viscosity
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Discussions about accuracy and precision of data and what level is
appropriate
Top GCSE and A’ level
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Hydrogen bonding
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Curing (properties will change with time)
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Creep (and an analogy to convection in the mantle of the Earth or
metals)
…and more besides.
PVA adhesive is non toxic, but is not edible.
Borax is poisonous if swallowed and may cause skin irritation where students
have sensitive skin or an allergy. Borax has been used as a domestic water
softener, a mild antiseptic and domestic cleaner, though today, these
applications are generally superseded by more commercial products.
Viscous Goo Challenge - Teachers’ Notes
PVA adhesive (wood glue / white paper glue) will vary in composition
depending on its source, so it is necessary to try quantities for yourself. White
paper glue mixed with water in a 1 :2 ratio (glue to water) has been found to
give consistent results. PVA could stand for Poly Vinyl Alcohol or Poly Vinyl
Acetate. In fact glues are probably a mixture of the two, but since both are
polar and can interact with borax, this is not important for the experiment.
PVA is non toxic; Borax would be poisonous if consumed but (other than
occasional skin irritation) is harmless. Uses include mild anti-septic, fridge and
kitchen surface cleaner, water softener. Until recently borax was readily
available from chemist shops. The solution used is made as a saturated (4%)
solution prior to use.
The behaviour of Goo is useful as a discussion on solids and liquids (stretches
if pulled slowly, snaps if pulled quickly). The flow of goo on a bench surface
illustrates creep. Creep is common in polymers and metals at about 1/3 mpt
(lead is a good example). Also convection currents in the solid mantle of the
earth can be describes as creep in a ceramic material. Although not the same
process, there are similarities with bonds being broken and reforming in a
different position. Whereas Goo will creep by several cm in a few seconds,
lead will take centuries and the mantle takes millennia.
Experiments can be aimed at KS2 to A-level, from purely fun activities to
simple experiments illustrating changes in physical properties of polymers due
to cross linking and intermolecular forces (Hydrogen Bonds).
It is possible to develop investigations based on the above experiments,
particularly the sinking coin by linking this to the amount of borax used on a
fixed amount of PVA.
Viscous Goo Challenge
Plastics (polymers) are large chains of repeating molecules. We can sometimes
change the properties of polymers and make them into more useful materials by
joining up the separate chains using chemical bonds. This is called crosslinking.
Chains of PVA (Poly Vinyl Alcohol) can be (loosely) cross-linked by adding
borax solution. This results in the PVA changing from a liquid to a rubbery
slime.
Polymer chains can slide past each other under the effect of a force. Liquid
polymers are viscous (thick, not very runny liquids) because of forces between
the chains. We can change the viscosity by changing the way that the chains
slide past each other – effectively changing the friction between them.
More force/friction = harder for chains to slide past = more viscous liquid.
Polymer chains are
tangled together
Forces make the chains slide Cross linking stops the
past each other and line up. chains from untangling.
PVA molecules and how they interact
Polymer Chain
Alcohol Group (Covalent –OH )
The alcohol groups interact weakly and the chains
tangle. This slows the molecules down when they try
to slide past each other, making the polymer behave
as a viscous (treacly) liquid.
PVA molecules with Borax
Polymer Chain
Alcohol Group (Covalent –OH )
Cross-Link: Strong Attractive Force
(Hydrogen Bond can be broken and re-formed easily)
Borate Anion: [B(OH)4]2The cross-link causes a MUCH stronger interaction,
making the material MUCH more viscous and can even
give the appearance of being a solid.
(Note: if the cross link was made using a stronger, full
covalent bond, then the material would be a solid: e.g.
rubber and thermosetting polymers.
Your challenge:
Design and test:
 The slime with the greatest bounce.
 The slime that can stretch the most without breaking.
 Investigate the viscosity of slime as a function of the amount of borax
used
Your time limit is 30 minutes.
 5 minutes to make a plan.
 10 minutes to carry out your plan.
 10 minutes to carry out your tests.
 5 minutes to clean up the mess.
The basic recipe for the slime is given below.
Chemical and Apparatus Lists
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250 ml bottle of 25% PVA solution (shared).
250ml beaker of saturated Borax solution (shared).
Borax is a >>>-  POISON  -<<< Wash your hands after using it!!!
Plastic dropper (each).
100 ml beaker (each).
Food dyes (optional).
Stirring rod (each).
Procedure
Use the scale on the side of the 100ml beaker to measure 20ml of the PVA
solution. You may need to estimate from the scale. Ask for help if you are not
sure about this.
1. OPTIONAL – you can stir in one (or two) drops of food colouring at this
point.
2. Add between 1 and 10ml of the 4% borax solution. (Note: It’s best if
each member of the team agrees to investigate a different amount
of Borax – organise this between yourselves e.g. 2, 4, 6 etc ml.)
3. Stir vigorously for several minutes until the solution has gelled. You may
find that you have to scrape the GOO from the rod several times before
you get an even mixture. The more stirring you give, the better the GOO.
4. Wash your hands before eating or drinking anything. Borax is a poison
if swallowed.
Testing viscosity – this is one possible method: feel free to test your own.
1. Prepare samples of slime made with different amounts of borax (2, 4,
cm3 etc.)
2. Leave to settle in a small beaker.
3. Place a coin on the surface and time how long it takes to sink.
4. Draw a graph of time to sink (viscosity) against volume of borax solution
used.