It stretches. It shimmers. It shatters. It shapes endless possibilities, and I can’t seem to put it down for very long. My Smart Mass Thinking Putty, a souvenir from Science Online last week, is simultaneously the best and worse toy to enter my life in a long time. I took it to my office, thinking that it could serve as occasional thinking aid or minor stress relief. Major mistake. I can barely put the putty down to put my fingers to the keyboard.
I should have known this was a bad idea. During the #scio12 banquet, I opened the tin, and proceeded to play with the putty through the entire evening’s entertainment. Waiting in line for the bus, despite lively conversation, I tried to sneak into the tin to touch the putty. It’s that addictive. So what makes this putty the object of my serious obsession?
Part of the awesomeness, aside from the shifting color, is that the putty sometimes stretches into long, thin strings, but at other times, will tear with a snap. It’s like a solid and a liquid simultaneously. How do they put so many physical properties into one putty? The secret recipe isn’t published, but the main ingredient is a silicone named Polydimethylsiloxane. It’s a silicon based polymer, which means that it’s a large structure of repeating molecules, held together by the bonds that form when adjacent molecules share electrons.
What makes PDMS special is that it exhibits different flow behavoirs at different time scales. Left alone for a long time, it will spread out into a smooth pool, like a liquid, in it’s tin. If you watch the video below, you can see that if you smash a lump of the putty with a hammer, it will shatter into pieces, like breaking glass or ceramics, because the impact occurred so fast. If you roll it into a ball, and throw it at your desk, it will bounce. If you pull it quickly, it will tear, slowly it will stretch. In between overnight in the tin and a quick blow with hammer, it stretches like a plastic solid. This ability to act both like a liquid and also stretch like elastic, is called viscoelasticity.
In the video below, they show you all the different behaviors of the Smart Mass (new magnetic putty, which I am craving now) that occur on the different time scales.
Below, the putty demonstrates it’s liquid behavior on a long time scale. The images are from a 12 minute period, sped up to watch over 24 seconds.
Another key ingredient in my putty is boric acid, which contributes to the elasticity of the compound. The boron molecules form constantly shifting weak linkages, creating a solid that is always held together enough not to behave like a liquid, but flexible enough to stretch and stretch some more.
My putty, as you can see in the photo above, in a beautiful shimmery green. But they sell all kinds of colors, including a clear putty, one that changes color by reacting to the heat from your hands, and a black magnetic putty. So, I think I already know what I am buying everyone for presents this year.