Magnetic-Induced Actuation of Fe₃O₄-Hydrogel Composites Incorporating with Functionality of Capacitor AITranslate

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Basic Information:

DOI：10.13373/j.cnki.cjrm.XY23010008

Chinese Library Classification Number:TB332

Citation Information:

With the rapid development of robotics，the intensive interactions between robots and humans/environment require the development of flexible actuators capable of attenuating external shocks and adapting in complex environments. In the large family of flexible materials，magnetic-induced flexible robots have been widely used in closed environments due to the penetrability，fast response and nondestructive characteristics of magnetic fields. Compared with other robot actuation methods，magnetic-induced actuation has many advantages，including the realization of wireless drive through most materials. By controlling the direction and intensity of the magnetic field，the robot can be accurately manipulated. Among magnetic-induced composites，the most common material is hydrogels. Hydrogel is a three-dimensional network structure formed by cross-linking macromolecules through chemical or physical actions，with flexible and adjustable functional properties. Since hydrogels absorb water by interacting with water molecules but do not dissolve，they can effectively bind solutions containing conductive ions in their polymer networks，achieving ionic conductivity while avoiding the problem of liquid leakage. At the same time，hydrogel materials usually have amazing stability under electric fields and can exhibit excellent functional properties even at 15 V. So，they can protect the water molecules inside them from electrolysis and facilitate the stable realization of their functions under the action of electric fields. After incorporation of magnetic particles，hydrogels can also be endowed with the ability to respond to magnetic deformation. However，the weak mechanical strength of most hydrogel electrolytes largely limits their applicability. In order to supply a new opinion for the preparation of hydrogel electrolyte with excellent mechanical properties，a capacitor was prepared based on polyvinyl alcohol （PVA）/NaCl hydrogel，MnO₂ and Fe₃O₄ used as cathode and anode materials to provide capacitance and magnetic response capabilities. The types of the materials in the samples were systematically analyzed by means of X-ray diffraction analysis （XRD），Fourier transform infrared spectroscopy （FT-IR） and Raman spectroscopy. In addition，the finite element analysis model of magnetic-responsive hydrogel was established. The mechanical effects of different magnetic fields were simulated by finite element analysis （FEA） software. By adjusting the direction and magnitude of the magnetic field and the elastic modulus of the material，the regulation of strain adjustment was clarified. FEA software was used to analyze cyclic voltammetry （CV） curve of the ideal hydrogel actuator under different magnetic fields. Because the area of the electric double layer of the capacitor was closely related to the area of the electrode，the parameters of the electric double layer were set in direct proportion to the percentage of the change of the electrode area. The simulation results showed that the area of the double electric layer before （0 mT） and after （100~500 mT） the strain was only slightly changed （less than 0.5%）. And then，the electrochemical performances of hydrogel actuator were examined by CV and galvanostatic charge-discharge （GCD） tests on electrochemical workstation. The electrochemical properties of the hydrogel actuator were tested by two-electrode test system. In the two-electrode system，carbon nanotube （CNTs）/MnO₂ and CNTs/Fe₃O₄ was used as the anode and cathode. The hydrogel actuator was placed in different magnetic field intensities and its electrochemical performance under different strains was tested by electrochemical workstation. The results showed that CV curves of the hydrogel actuator showed a symmetrical quasi-rectangular shape and always maintained good symmetry as the scan rate increased，indicating that the hydrogel actuator could withstand rapid voltage/current changes. The specific capacitance changed from 13.27 to 4.99 F·g⁻¹ when the scan rate increased from 1 to 50 mV·s⁻¹. GCD plots curve had an approximate isosceles triangle shape，demonstrating that the charge-discharge behavior was highly reversible. The corresponding specific capacitance calculated by GCD plots was from 3.74 to 1.67 F·g⁻¹ when the current density increased from 0.01 to 0.3 A·g⁻¹. The performance of the hydrogel actuator based on traditional aqueous electrolytes often degraded or internal short circuits under external forces such as bending，twisting，stretching and shearing. In order to estimate the electrochemical stability of the prepared hydrogel actuator under external stress disturbance，the electrochemical performances of the hydrogel actuator were tested under different bending angles. At the same scanning rate，when the magnetic field intensity increased from 0 to 100 mT，the integral area of CV curve had a 1% area change. Similarly，under the same current density，GCD plots did not change with different bending angles （the charge discharge time difference under different magnetic field intensities was 0），indicating the stability of the hydrogel actuator after strain under different magnetic field intensities. When the magnetic field intensity increased to 100 mT，the specific capacitance increased by 2.5%. When the magnetic field intensity increased to 500 mT，the specific capacitance of the hydrogel actuator was 5.44 F·g⁻¹，which was 0.6% higher than the specific capacitance under 100 mT. The results showed that the prepared hydrogel actuator could withstand certain bending and had good capacitance retention. In addition，the calculated specific capacitance according to GCD plots indicated that the hydrogel actuator maintained the same specific capacitance after strain under different magnetic field intensities，which further illustrated the stability of the hydrogel actuator.