ABSTRACT
The motion of magnetic particles under magnetic fields is an object to be solved in association with basic and practical phenomena. Movement phenomena of magnetite-encapsulated graphene particles at air-water interfaces were evaluated by manufacturing a feedback control system of the magnetic field to cause the motion of particles due to magnetic torque. A homogeneous magnetic field was generated using two pairs of electromagnets located perpendicular to each other, which were connected to an electronic switch. The system influenced the translational movement and the self-rotational speed of magnetic particles located at a center on the surface of fluid media in a continuous duty cycle. Operating the particle at a remote control in the same duty cycle at the air-water surface, the short and elongated magnetic particles successfully rotated. In addition, the rotational speed of the curved particle was slower than that of the elongated particle. The results indicate that the translational and self-rotational movements of magnetite-encapsulated graphene particles at the air-water interface under the external magnetic field are size- and shape-dependent for the speed and the direction. A short magnetic particle was used as a target particle to rotate on cancer cell lines, aiming to study the advantage of this method to induce the growth of HeLa cells. It was monitored for up to 4 days with and without magnetic particles by checking the viability and morphology of cells before and after the electromagnetic treatment. As an outcome, the movement of magnetic particles reduced the number of biological cells, at least on HeLa cells, but it was inactive on the viability of HeLa cells.
ABSTRACT
The effect of conductive materials (polyaniline (PA) or carbon dots (Cdots)) added to supercapacitor consisting of nitrogen-doped graphene oxide (NG) and magnetic nanoparticles (magnetite, Fe3O4) was assessed. Small amounts (4 wt%) of Cdots in composites of NG and Fe3O4 nanoparticles have shown better supercapacitor performance than the addition of PA. When the external stimulating force (magnetic field, 8.98 mT) was coupled with the electrochemical system, the specific capacitance was highest (2213 F/g at a scan rate of 5 mV/s) and the cyclic retention was 91% after 5000 cycles for the NG/Cdots/Fe3O4 composite electrode. These reports show that the adequate ternary composite materials effectively enhance the specific capacitance, increase the specific energy density and maintain the durability of supercapacitors under the magnet. The increase in the specific capacitance under the uniform magnetic field was proportional to the 3/5 power of bulk electrolyte concentration, although the power value was different from the theoretical estimation. The complex capacitance was almost double under the magnetic field due to the convection induced by the Lorentz force. It was also confirmed in comparison with the theoretical estimation that the Lorentz effect was responsible for the reduction of the charge transfer resistance, the increase of the relaxation time constant, the facilitation of the ion diffusion, and hence the increase of the double-layer capacitance. The present results will open a new window for the enhancement mechanisms on the capacitance efficiency under the magnetic field.
