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Portal 2 Interactive Gels, Science, and You!

How to rip and tear your Portal 2 Interactive Gels

Don't pull and stretch it to get two pieces; that takes forever. Tear it, instead! Hold the putty as seen in the photograph. Dig the nails of your thumbs and forefingers into the putty.

With a quick and sure motion, just rip it! On the first couple of tries, you may end up just stretching the putty. Try to move quicker with more force. You'll get it eventually.

Some Science: Normally when you stretch your Portal 2 Interactive Gels, the molecules realign themselves with the direction of motion. Herding together like sheep, they stay attached to each other and let you stretch. By moving quickly, you don't give the molecules inside the putty time to realign themselves with the direction of motion. Instead of flowing, they tear apart.

How to witness your Portal 2 Interactive Gels behaving like a liquid

This is a great trick that always elicits a great response. The first step it to take a big handful of Portal 2 Interactive Gels and make a symmetrical cylinder (pictured is two tins worth, but one works just as well). Next, stand on a chair, ladder, coworker, table, or use Portal technology to firmly stick yourPortal 2 Interactive Gel to the ceiling. Give the cylinder a little squeeze about three quarters of the way down (closer to the part now facing the ground).

Now watch and wait. Slowly the putty below where you squeezed make its way to the table/floor/etc. If you've gotten your indentation right, you can watch a thin strand of Portal 2 Interactive Gel pouring from the ceiling. It's like watching molasses run, only cooler! It's hypnotic and can last a really long time with a little luck and a little practice.

How to shatter your Portal 2 Interactive Gels

If you strike your Portal 2 Interactive Gels with a hammer, they will shatter. But why? Becasuse Portal 2 Interactive Gels are dilatant compounds, which means it becomes solid under the influence of pressure. If you've ever played with Oobleck, you've experienced the same properties.

And now for even more SCIENCE!

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 (ex. concentrated aqueous corn starch suspensions).

However on its own, this is not enough to explain the behavior of your Portal 2 Interactive Gels. 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.

Due to the Boric acid (the fourth ingredient by weight), there are also transient Boron mediated crosslinks arising from associating Boron linkages. These act to give the Portal 2 Interactive Gels 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 Portal 2 Interactive Gels behave like a high molecular weight polymeric fluid. Over very short time scales the putty behaves like a crosslinked elastic solid, shattering like a ceramic on impact.