Swelling degree and shape change of photo- and thermo-response of spirobenzopyran-functionalized porous pNIPAAm hydrogels

Novel hydrogels that shrink in response to light irradiation and temperature change have been developed. Since any technical application of polymer gels critically depends on the response rate, therefore porous hydrogels have been prepared in order to accelerate the response reaction. Poly(N-isopropylacrylamide) gels were functionalized with photo-responsive spirobenzopyran and solvent/nonsolvent mixtures were used as swelling agent to introduce network heterogeneities during the gelation process. Both photo- and thermo-responsive properties of gels have been investigated and compared. The time dependence of bending deformation due to the asymmetric light irradiation as well as kinetics of shrinking has been measured. It was found that the fastest photo- and thermo-responsive shrinking was observed for loosely crosslinked porous hydrogels. Furthermore, it was confirmed that the highly cross-linked cylindrical gel rod with macroporous structure showed rapid bending deformation due to the asymmetric light irradiation.