Thursday, April 8, 2010

What is Silly Putty Made Of? GUEST BLOG

Todays guest blogger is Trent.
It said that silly putty was made of polymethylsilicane molecules crossed-linked with boron-based molecules, essentially silicone oil mixed with borax.
Polymethylsilicane sounds impressive but it's simply a polymer, a very long molecule consisting of a series of small identical molecules linked end-to-end in a chain, in other words: plastic. Think of it as a piece of spaghetti. A large quantity of these spaghetti-like molecules flow like a liquid because they are able to slip and slide around each other.

But, mix some of this oily liquid with boric acid (almost the same thing as water with a little Borax laundry booster in it) and some of the Borax molecules will stick to the sides of the long plastic molecules and in so doing create bridges (cross-links) between them that mechanically bind them together. Think of the Borax cross-links as pieces of very sticky rice. These rice particles glue the long spaghetti strands together and prevent them from slipping past one another. If there is a small amount of cross-linking the result is a slimy goo the consistency of honey. If the amount of cross-linking is very high these bridges between the long molecules lock everything up and you have a block of hard plastic. But, if the amount of cross-linking is just right the resulting material is soft enough to mold and you have Silly Putty.

So far so good. The spaghetti and sticky rice analogy gives us an idea of what Silly Putty looks like on a molecular level, but that doesn't explain its unusual abilities to slowly flow like a liquid, stretch to incredible lengths, bounce like a rubber ball and shatter like glass if struck with a hammer.


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