Tangled Molecules

    Kids, did you ever watch someone make spaghetti? If there are just a few cooked strands in a boiling pot of water, chances are they won't touch each other. But when a whole box is cooking the strands can't avoid touching each other. Some molecules are so long and skinny that they act like strands of spaghetti. In this experiment we will see how the long, skinny molecules called polymers can sometimes behave the same way.  

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

    To one-half cup of cold water add anywhere from 5 to 10 heaping tablespoons of household corn starch, one at a time with complete mixing each time. The amount varies with the quality of both the water and the cornstarch. You will know you have the right amount when the following tests work. Do you notice a difference between stirring very slowly and stirring faster, or between slowly lifting the spoon out and quickly pulling it out? How about putting your finger in slowly and touching the bottom of the bowl vs. jamming it in?

    The starch mix should act almost like a solid when confronted with a fast motion. This is because the long, skinny starch molecules are very crowded and get tangled up with each other. When a slower motion is used, the molecules have enough time to move out of the way of each other (just like spaghetti!). Disposal: The mix gets thicker on standing, so immediately after finishing pour it into a large bowl of water and wash down the drain with lots of water.


    Kathleen Carrado Gregar, PhD, Argonne National Labs 
    [email protected]
    April 1993