A swell polymer that has three-dimensional networks, and is
solidified sol (colloidal solution) in a jelly form.
A polymer gel that changes its volume by changes of ion
concentration in solution, thermal fluctuations, chemical reactions, electric stimuli, or light
stimuli, and so on is called the mechanochemical or chemomechanical material. These gels are the
nonelectrolyte polymer gel (polyvinyl alcohol ;PVA) in which the changes of solvent composition make
the polymer chains and the solvent act on each other, thermal reversible composite (methyl cellulose
water solution), electrolyte gel (polyacrylonitrile) that contracts at changes of ion concentration,
electrolyte gel (polyvinyl alcohol) that responds to electric stimuli, and one that responds to
light stimuli (polyacrylic amide). Use of gel for micromachines, especially for artificial muscles
and drug delivery system (DDS) is being studied.