Making slime with PVA glue

It seems that slime is a current craze amongst older children than mine (the small boy has thankfully not yet reached the age where he's influenced by the fashions for particular toys), and as a result there are lots of 'recipes' around to make it at home. Despite it being popular with older children, I thought he might find it fun.  It would give us an opportunity to play with a non-Newtonian fluid again (we tried cornflour and water before, which I've since learnt is called 'oobleck') and to try a new type of chemical reaction than our usual acid and alkali experimentation.

The method we tried was to mix PVA (polyvinyl acetate) glue with bicarbonate of soda and contact lens solution. The quantities we used were 100g, half a teaspoon and one-and-a-half tablespoons respectively. I wouldn't recommend this (see later for why) though.

The small boy happily mixed some green food colouring into the glue first with a lolly stick, then he added the bicarbonate of soda and gave it a mix. I helped him mix it in a little more evenly and then we poured in the contact lens solution together.  There was no particular reason for green, although I think I might subconsciously have been influenced by the film 'Flubber' from my own childhood!

The contact lens solution contains boric acid. When added to bicarbonate of soda, borate ions are released and react with the PVA glue, forming cross-links between the polymer chains in the glue. This is an endothermic reaction which means it gets cold - the small boy was able to notice this (with prompting to ask if it was getting hotter or colder) by holding the plastic beaker that we made the slime in.

Mixing the ingredients of slime

The slime itself went, well, slimy as expected. It was a gooey substance that stretched, which was neither solid nor liquid. I thought he might like to play with shaping it in his hands but he touched it once and refused to do as much as poke it with his fingers again. It did feel pretty weird, and he's not a fan of getting messy hands or things with strange textures (e.g. he refuses to do finger painting and was pretty horrified when I tried to get him to play with some jelly a few months ago), so I shouldn't have been surprised.

I didn't want the slime to be a total flop and instead I decided to try something else and found a couple of goggly eyes and some more lolly sticks and invited him to create 'monsters' by poking them into the slime. He was pretty keen on this - he could do it without touching the slime if he told me what shape to make, and he set about making monsters with different numbers of eyes, arms, legs and antennae which occupied him for about 10 minutes.

One of the small boy's slime 'monster' creations

The slime was pretty disappointing though as after about an hour back in the beaker, there was a layer of watery liquid. I tipped it off and the same thing happened again, and the slime hardened pretty fast.   I'd been hoping we'd make something that was reuseable for a few days, but sadly this was only useable for a few hours.  I've seen other 'recipes' with additional ingredients such as cornflour or shaving foam, and I think when we next try this I will test out another method. However, we won't be doing it again in a hurry given my son's reluctance to really interact with the slime!