The reversible volume change of gels upon external stimuli was shown, for the first time, by Tanaka et al. 1 After this discovery, much effort has been made on the synthesis and application of the stimuli-responsive gels, especially those of hydrogels, in view of their scientific and technological importance. 2 A wide variety of external stimuli are available for the volume change of gels, including temperature, pH, solvent composition, and so on. ...
