Property of magneto-driven poly (N-isopropylacrylamide) gel containing γ-Fe2O3 in NaCl solution as a chemomechanical device

Magnetically triggered phase transition of the hydrogel was applied as a chemomechanical device. The thermosensitive poly (N-isopropylacrylamide) gel immobilized with γ-Fe2O3 deswelled spontaneously due to generation of heat through magnetic hysteresis loss under the alternating magnetic field. The initial rates of stress generated by the gels prepared in water and in 0.8 M NaCl at 22°C were 0.04 and 0.75 kPa s−1, respectively. The lower critical solution temperature decreased from 34°C (in water) to 24°C (in 0.8 M NaCl solution). A bundle of 20 gel rods (Φ=0.7 mm) in 0.8 M NaCl could lift the weight (20 kPa as tensile strength) within 90 s with deswelling, and then swelled and returned to its original length in 15 min repeatedly. Efficiency of the energy conversion, from the heat due to hysteresis loss of γ-Fe2O3 to the mechanical work of the device, was also investigated.