Dual electro- and magneto-induced bending actuators of magnetite-loaded agarose ionogels.

Magnetic ionogels are a new kind of gel composites which combine the elastic properties from the swollen gel matrix and the magnetic properties from a magnetic filler. The dual electro-magneto-responsive agarose ionogels (AG IGels) were fabricated by a solution casting method using 1-butyl-3-methylimidazolium chloride [Bmim][Cl] as the ionic liquid solvent, and embedded with magnetite nanoparticles (Fe3O4 NPs). The addition of Fe3O4 NPs induced the high bending responses under applied electric and magnetic fields via the electronic polarization and magnetic interaction. The 3.0 wt.% Fe3O4/AG MagIGel showed the largest deflection distances relative to other magnetic gel composites; 14.92, 8.96, and 21.63 mm under the applied electric fields of 600 V/mm in silicone oil, 60 V/mm in air, and under the applied magnetic field of 600 G in air, respectively. The bending distances were of comparable in magnitudes to other electro-magneto-responsive materials. Thus, the fabricated Fe3O4/AG MagIGels are demonstrated here as potential for soft electric-magnetic actuator applications.

Synthesis and Characterization of Fe0.8Mn0.2Fe2O4 Ferrite Nanoparticle with High Saturation Magnetization via the Surfactant Assisted Co-Precipitation.

Manganese ferrite nanoparticles (MnFe2O4) were synthesized via surfactant-assisted co-precipitation, where sodium dodecyl sulfate (SDS) was used as the template to control particle size at various SDS concentrations. The substitutions of iron (II) (Fe2+) into the MnFe2O4 ferrite nanoparticles were carried out to obtain Fe(1-x)MnxFe2O4, with various Mn2+: Fe2+ molar ratios. The synthesized ferrite nanoparticles were characterized by the Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analyzer (TGA), X-ray diffractometer (XRD), energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), two-point probe, and vibrating sample magnetometer (VSM) techniques. The experimental Mn:Fe mole ratios of the Fe(1-x)MnxFe2O4 ferrite nanoparticles were verified to be in agreement with the theoretical values. The synthesized MnFe2O4 and Fe(1-x)MnxFe2O4 ferrite nanoparticles were of mixed spinel structures, with average spherical particle sizes between 17-22 nm, whereas the magnetite ferrite nanoparticles (Fe3O4) were of the inverse spinel structure. They showed soft ferromagnetic behavior. The synthesized Fe0.8Mn0.2Fe2O4 ferrite nanoparticle possessed the highest saturation magnetization of 88 emu/g relative to previously reported work to date.

Facile formation of agarose hydrogel and electromechanical responses as electro-responsive hydrogel materials in actuator applications.

The agarose hydrogels (AG HyGels) were fabricated by a solvent casting method at various agarose concentrations, resulting in the 3D hydrogel networks via the physical crosslinking from the hydrogen bonding. The actuator performances were investigated at various agarose contents and electric field strengths. For the electromechanical properties, the AG HyGel_12.0 %v/v possessed the highest storage modulus (G') and storage modulus relative response (ΔG'/G'0) of 4.48 × 106 Pa and 1.07, respectively under applied electric field strength of 800 V/mm due to the electrostriction effect. In the electro-induced bending measurement, the highest deflection distance was obtained from the AG HyGel_2.0 %v/v due to its initial lower rigidity. Relative to other bio-based hydrogels, the present AG HyGels are first demonstrated here as electroactive materials showing comparable magnitudes in the electroactive responses, but with the simple fabrication method without toxic ingredients required. Thus, the present AG HyGels are potential material candidates for soft actuator applications.

Influence of carrageenan molecular structures on electromechanical behaviours of poly(3-hexylthiophene)/carrageenan conductive hydrogels.

The κ, ι, and λ carrageenans were fabricated by solution casting as soft and electrically responsive actuators. The poly(3-hexylthiophene) (P3HT) was added as a dispersed phase to improve the electrical and electromechanical properties of the pristine carrageenan hydrogels. The electromechanical properties of the carrageenan hydrogels were investigated under the effects of electric field strength, carrageenan type namely κ, ι, and λ, operating temperature, and P3HT concentration. The electromechanical responses of the pristine carrageenans increased with increasing sulfated groups present; the λ-carragenan hydrogel provided the highest storage modulus sensitivity of 4.0 under applied electric field strength of 800 V/mm. With increasing temperature, the double-helical structure of the κ-carrageenan hydrogel changed into a random coil leading to the increase in the storage modulus response. On the other hand, the P3HT/κ-carrageenan hydrogel blend at 0.10%v/v P3HT provided the high storage modulus sensitivity of 2.20 at the electric field strength of 800 V/mm. The higher dielectrophoretic forces were due to the additional P3HT electronic polarization, but lower deflections relative to those of the pristine κ-carrageenan hydrogel. Both κ- and λ-carrageenans with the double helical structures are shown here as possible candidates to be fabricated as electroactive hydrogels for actuator or biomedical applications.

Soft poly(2-chloroaniline)/pectin hydrogel and its electromechanical properties.

Pectin hydrogels were successfully fabricated with various physical crosslinkers and concentrations for soft actuator applications. A small amount of synthesized P2ClAn was added as a dispersed phase into the pectin matrix. The electromechanical properties of the pectin hydrogels and blends were investigated under the effects of electric field strength, ionic crosslinker type and concentration, and P2ClAn concentration. The electromechanical properties of the pectin hydrogel as crosslinked by Fe2+ were superior to other pectin hydrogels. The pristine pectin hydrogel and the P2ClAn/Pectin hydrogel blended with 0.10%v/v P2ClAn provided the high storage modulus sensitivity values of 8.61 and 14.01, respectively, under the electric field strength of 800 V/mm. The P2ClAn/Pectin hydrogel blend responded to the electric field with higher dielectrophoretic forces, but lower deflections relative to the pristine pectin hydrogel due to the additional P2ClAn polarization and the latter lower rigidity.

Electrically responsive materials based on polycarbazole/sodium alginate hydrogel blend for soft and flexible actuator application.

The electromechanical properties, namely the storage modulus sensitivity and bending, of sodium alginate (SA) hydrogels and polycarbazole/sodium alginate (PCB/SA) hydrogel blends under applied electric field was investigated. The electromechanical properties of the pristine SA were studied under effects of crosslinking types and SA molecular weights, whereas the PCB/SA hydrogel blends were studied under the effect of PCB concentrations. The storage modulus sensitivity and bending of the pristine SA as crosslinked by the ionic crosslinking agent were found to be higher than those of the covalent crosslinking. The storage modulus sensitivity and deflection of the SA increased monotonically with increasing molecular weight. The highest electromechanical response of the PCB/SA hydrogel blends was obtained from the blend with 0.10% v/v PCB as it provided surprisingly the highest ever storage modulus sensitivity, (G'-G'0)/G'0 where G'0 and G' are the storage modulus without and with applied electric field, respectively, at 18.5 under applied electric field strength of 800V/mm.