ABSTRACT
What do soft contact lenses, disposable diapers, and sanitary towels have in common? They all absorb a lot of body ¤uid. Superabsorbers are made of a crosslinked network of polyacrylate. The network may be considered a highly concentrated salt where sodium ions neutralize the carboxyl groups along the polymer chains. Polyacrylate is well soluble in water, and due to osmosis, the network sucks up the aqueous body ¤uid. The sodium ions become hydrated and dissociate from the carboxyl groups. The negatively charged carboxyl ions repel each other, which causes the polymer chains to stretch and the network to swell. This creates more space for the ¤uid to enter. A hydrogel is thus formed in which the amount of absorbed water may exceed 50 times the dry weight.
