ABSTRACT
Hydrogels are attractive objects consisting of cross-linked networks of polymer swollen with aqueous solutions, and have both liquidlike and solidlike properties. As hydrogels have a variety of properties including their sorption capacities, swelling behavior, mechanical properties, permeabilities, surface properties, and optical properties, they are highly promising materials for wide applications in various fields such as medicine, agriculture, and biotechnology (15). Such fascinating properties of hydrogels are governed by the characteristics of polymer chains in aqueous solutions and the cross-linking structures. In general hydrogels, the cross-linked polymer networks are formed by covalent bonds, electrostatic interactions, hydrogen bonding, hydrophobic interactions, van der Waals forces, physical entanglements, crystallite, and so on. The polymer chains in hydrogels are generally hydrophilic and compatible with aqueous solutions to be swollen. Therefore such crosslinked structures and polymer chains must be designed for developing useful hydrogels for a given purpose.
