A hydrogel is a solid material that absorbs water and swells to form a network. It consists of polymer chains that are cross-linked to form a three-dimensional structure. When dry, the polymer chains are collapsed, but when placed in water, the chains hydrate and expand to create a gel-like swollen network. Common examples of hydrogels include the superabsorbent polymers used in diapers to absorb moisture and gelatin, which forms a solid gel when cooled from a liquid state due to the cross-linking of gelatin molecules.

1. Hydrogels

2. WHAT IS A HYDROGEL?
Hydro=Water
Solid that absorbs
water
So, what does the solid
part look like?

3. Many Small
Molecules
One Large
Molecule
POLYMER

4. CROSS-LINKING = POLYMER
NETWORK
http://soft-matter.seas.harvard.edu/index.php/Cross-linking
Polymer Chains
Crosslinks

5. EFFECT OF WATER
Dry solid
(collapsed)
Hydrogel
(swollen
network)

6. DIAPER
http://disposablediaper.net/general-information/disposable-diaper-history/
What’s really going
on?
POLYACRYLAT
E hydrogel

7. HAVE YOU EVER MADE JELL-O?

8. WHAT’S IN JELL-O?
Gelatin
Structure

9. MAKING JELL-O &
WHAT HAPPENS WHEN YOU HEAT
IT?
Gelatin Powder
Water
Liquid Solid Hydrogel
cooling
re-heating