Articles

    Silly Putty

    Kids, did you know that Silly Putty®, in addition to being the pinkish, bouncing, stretchy stuff, is also a "dilatant" chemical compound? Silly Putty is a unique material. It stretches without breaking, yet it can be "snapped off" cleanly. It bounces higher than a rubber ball. It floats if you shape it in a certain way, yet sinks in others. It can pick up pencil marks from pages and comics from some newspapers. If you slam it with a hammer, it keeps it shape, yet if you push with light, even pressure, it will flatten with ease. Gravity has a slow, yet devastating effect on Silly Putty creations.

    Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

    All kinds of information can be found at:  www.sillyputty.com/default.htm.  There are even some experiments described there for you to try, such as "Floating Silly Putty", "Making It Bounce", "Silly Putty Running", "Squishing Silly Putty", and "Stretching and Snapping". We'll describe one here. When you shape Silly Putty into a ball it will bounce great on a hard, smooth surface. Cooling it actually improves its "bouncability." Shape it into a ball and bounce it. Measure how high it bounces. Then place the ball in the freezer for about an hour. While it's still cold, bounce it the same way you did when it was warm and compare the result. Silly Putty is said to have a rebound of 80 percent, meaning it will bounce back 80 percent of the height from which it was dropped.

    As we said before, Silly Putty is a dilatant - a silicone based polymer that is highly elastic, exhibits high bounce, can be easily molded, yet can hold it shape while at rest. It was invented by a chemist at General Electric who was working on synthetic rubber substitutes, at first by mixing silicone oil with boric acid. Warning, here are some more big words: a dilatant is a "non-Newtonian fluid" for which "viscosity" increases as the "shear rate" increases. This is called shear-thickening. There are four different kinds of non-Newtonian Fluids based on viscosity behavior and a dilatant is one of them. Examples of regular Newtonian fluids include water, soda, and gasoline; some non-Newtonian fluids are wet clay, Gack (12/94 ChemShorts), and starch in water (see 4/93 ChemShorts "Tangled Molecules").

    Silly Putty is also reported to be a "grip enhancer", used by athletes to increase hand strength. Unfortunately though it no longer lives up to what us older folks remember to be it's best quality. Changes in printing inks and processes, not in the putty itself, have limited its ability to pick up newspaper images. And just in case you or your parent needs to know, there is a method at www.crayola.com (see "Helpful Information") for removing Silly Putty from carpet.

    --------------

    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    kcarrado@anl.gov
    February 2003

    ----------------

    Reference: Ann Thayer, Chemical & Engineering News, 11/27/00, page 27. Dilatant info is at: www.sasked.gov.sk.ca/forum/science/archive/messages/1958.html