Two-wavelength-selective Soft Actuators Comprising Thermosensitive and Lanthanoid-ion-coordinated Interpenetrating...

Near-infrared wavelength-selective soft actuators have attracted much attention for applications in microsystems in bioliving. It is desirable for the photothermal conversion materials in the actuators to be downsized to the molecular scale. However, in conventional actuator materials using copolymer gels composed of thermosensitive and photothermal conversion molecule-coordinated monomers, the strong cross-linking of molecules in the networks impairs the actuator deformation. In this study, we fabricated soft actuators consisting of interpenetrating polymer network (IPN) gels to suppress the cross-linking of the thermosensitive networks. Nd³⁺ and Yb³⁺ were used as wavelength-selective photothermal conversion molecules at 808 and 980 nm. Hydrophobic acrylamide derivatives and sodium acrylate were used as the thermosensitive and lanthanoid-ion-coordinated polymers, respectively. The lanthanoid ion concentrations in the IPN gels were about 0.2 M, which is 6 times larger than those of previous gels. The temperature response of swelling degrees (wt%) of the lanthanoid-ion-coordinated IPN gels were three times larger than that of the previous gels. Sandwich structure actuators consisting of Nd³⁺ and Yb ³⁺ IPN gels bent selectively toward the Nd ³⁺ gel side under 808 nm irradiation and toward the Yb³⁺ gel side under 980 nm irradiation.