Magnetically Driven Chemomechanical Device with Poly(N-isopropylacrylamide) Hydrogel Containing γ-Fe2O3

Magnetic heating was applied to convert magnetic energy into chemomechanical work by using poly(N-isopropylacrylamide), poly(NIPAAm) gel, exhibiting a reversible swellingshrinking property. y-Fe ₂ O ₃ , which can generate heat by itself due to hysteresis loss in the presence of an alternating magnetic field, was immobilized within poly(NIPAAm) gel. The shrinking rate of the hydrogel accelerated when the inner temperature of the gel was increased over 34°C, the lower critical solution temperature (LCST). The initial rate of the temperature increase, which was in proportion to the amount of immobilized ferromagnetic powder, was 0.2°C/s in the gel immobilized 24% of the y-Fe ₂ O ₃ weight under the alternating magnetic field (effective value 830 Oe, maximum value 1,170 Oe, 2.08 kHz). Cylindrical poly(NIPAAm) gel rods immobilized 24% y-Fe ₂ O ₃ , which was crosslinked by 5% N,N'-methylenebisacrylamide, were able to generate mechanical force. Five gel rods whose cross-area was 1.5 x 10 ^-1 cm ² at 22°C could lift 20 g of weight up and down repeatedly by using contractile property of the gels. Shrinking of the gel rods was completed within 2 min. The hybrid poly(NIPAAm) gel containing the ferromagnetic powder could generate heat from inside and shrink spontaneously in the presence of the magnetic field. The magnetically driven chemomechanical device, which can convert magnetic energy into mechanical work, was studied using the hybrid hydrogel which was applied under the magnetic induction heating.