With suitable force exerted, the putty can even be shattered.Īs well as it’s obvious appeal for entertainment value alone, silly putty has actually found some serious uses. However, when the putty is pulled with suitable force, the crosslinks do not have time to break and reform, so elastic behaviour is seen. This means we are able to see the viscous flow of the putty. When the putty is slowly molded, the crosslinks have time to break and reform at different points in the polymer chains. These ‘crosslinks’ help hold the putty together, and also contribute to its properties. The boric acid can react with these to form transient boron-mediated linkages between different polymer chains.
The PDMS chains in silly putty end in OH groups. Another ingredient in the mix, boric acid, also makes a decisive contribution.
However, the viscoelasticity of PDMS alone isn’t enough to account for silly putty’s oddities. This is what causes PDMS’s viscoelasticity. The polymer chains are quite flexible, and when they are particularly long, as in the case of silly putty, they can become loosely entangled around one-another. This basically means that it is capable of flowing like a liquid in some cases, but behaves like an elastic solid in others. It’s what’s known as a viscoelastic solid. The properties of PDMS are partly responsible for silly putty’s properties.
Silicone polymers are, of course, more commonly known for their use in breast implants – and aren’t to be mistaken for the element silicon on its own, which would be a lot more uncomfortable! PDMS is a type of silicone, a group of polymers defined by the fact that they all contain Si-O-Si units as the basis of their polymeric structure. It’s the polydimethylsiloxane (PDMS for short) that’s a large contributor to the strange properties of silly putty, however. It flows imperceptibly slowly, as if it were a thick liquid, but when rolled up into a ball will bounce if thrown at a hard surface. A closer look at the chemicals that make up silly putty can help us explain this strange behaviour.Ī number of ingredients go into making silly putty: by weight, 65% of it is a compound called polydimethylsiloxane, but colouring agents are also included to give the wide range of colours that the putty comes in. However, pull it apart with enough force and it’ll snap clean in two. Stretch it slowly and it happily deforms, and can be molded very easily. Silly putty (or science putty, as it’s sometimes referred to) is an odd material.
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