Two-wavelength infrared responsive hydrogel actuators containing rare-earth photothermal conversion particles.

Two-wavelength infrared responsive soft actuators composed of rare-earth-oxide particles composited in a thermoresponsive hydrogel have been constructed. Because NdO and YbO particles possess independent narrow infrared adsorption at 808 and 980 nm, respectively, the vicinity of the particles in the gel can be individually heated by irradiation at each adsorption wavelength, inducing a local volume phase transition. The wavelength-selective volume phase transition can be controlled based on the combination of the particles incorporated in the gels and the wavelength of the irradiation laser at the optimized water temperature. Only the alternatively correct combinations successfully induced selective local clouding at the irradiation spots in the gel sheets. The original transparency of the gel was immediately recovered by turning off the light. Furthermore, rod-shaped block gels with NdO and YbO particles separately arranged on the left and right sides at the bottom of the rods were prepared to demonstrate wavelength-selective bending motion. The correct light combination caused reversible bending motion of only the side of the rod gel with the corresponding adsorbed particles.