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Watch Thinking Putty shatter when you hit it with a hammer!What happens when you hit Thinking Putty with a hammer? IT SHATTERS! Doesn't seem to make any sense does it? You play with Thinking Putty BECAUSE it stretches and melts and acts like a real liquid solid. So what's the skinny?The simple answer: Thinking Putty displays four different properties on four different time scales. At very long timescales, it behaves like a liquid spreading out onto a flat surface. At moderate timescales, the Thinking Putty stretches like a plastic solid. At short timescales, it bounces like an elastic solid. And, at very short timescales (the impact of a high-speed projectile), the Thinking Putty simply shatters. Thinking Putty is a dilatant compound, which means it becomes solid under the influence of pressure. If you've ever played with Oobleck, you've experienced the same properties. Now, let's see it in action! Check out the movies below and let me know what you think of them.
If you're careful, and don't mind taking a hammer to your own Thinking Putty, this experiment can be pretty fun. Don't forget eye protection, it is a must! The complicated answer for all you Chemistry Majors: Some of the behaviors listed above are an example of a dilatant compound, where the viscosity (i.e. the resistance to flow) increases faster than the strain rate. Although not common, some materials do exhibit dilatant behavior (concentrated aqueous corn starch suspensions -- read: Oobleck). However on its own, this is not enough to explain the behavior of Thinking Putty. In fact there are two mechanisms (and hence two characteristic time scales) at work. The high molecular weight of the primary ingredient PDMS (Poly Dimethyl Siloxane) has a characteristic polymeric relaxation time, defined by the time that a random walk allows the chain to relax from a stretched state through thermal vibrations. However due to the Boric acid (the fourth ingredient by weight), there are also transient Boron mediated crosslinks (and you thought I was kidding about the chemistry major bit) arising from associating Boron linkages. These act to give the Thinking Putty a behavior more like an elastic solid than a liquid. However since these crosslinks are dynamic, the material is not permanently locked in place and can consequently flow under the correct conditions. Therefore at longer time scales, the Thinking Putty behaves like a high molecular weight polymeric fluid. (Still here? Wow, you must be really interested!) Over very short time scales the putty behaves like a crosslinked elastic solid, shattering like a ceramic on impact. QED. Best,
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