Multiple Stimuli-Responsive Cellulose Hydrogels with Tunable LCST and UCST as Smart Windows

It has been a significant challenge to prepare multiple-response hydrogels with both lower critical solution temperature (LCST) and upper critical solution temperature (UCST). This work reports the synthesis of methyl cellulose-graft-polyacrylamide (MC-g-PAM) hydrogels by ceric ion initiated graft polymerization. Mechanically strong MC-g-PAM hydrogels combine LCST and UCST in one system (LCST > UCST), which provides a transparent "temperature window". The range of this temperature window can be tuned by changing cellulose contents or adding sodium chloride. In addition, the transmittance of MC-g-PAM hydrogels can be precisely controlled via application of varied DC voltage. These desirable properties make the MC-g-PAM hydrogels as smart materials.