Re: How does Sodiumpolycrylate or 'Water Loc' make water turn into a gel?

Dear Joy,

I'm sorry that you've had to wait for your answer... hope that it's not really too late.

I can't do better than direct you to a concise article entitled "Superabsorbers". Also try out "A Plastic that Grows", What is Sodium Polyacrylate good for, besides toys?", and "Yet Another Super absorbent Plastic!"

But in summary:

• Sodium polyacrylate (CH₂-CH)_nCOONa) is the sodium salt of polyacrylic acid (CH₂-CH)_nCOOH)
• It absorbs water due to its hydrophilic nature opening up the polymer chains to form a giant hydrogen-bonded sponge (in contrast we tend to think of most polymers as hydrophobic) somewhat analogous to gelatin.
• Salt removes the water because NaCl has an even stronger affinity for it. Ever poured salt on a slug? The effect on an onion is similar but less cruel.
• Iodized or uniodized, the effect will be the same.

If you need to buy the stuff for a demo, you can even purchase it online! Or you can break open a (clean) diaper!

Thanks for your question,
      A Mad Chemist with lots of diaper-changing experience!