Synthesis and Propulsion of Magnetic Dimers under Orthogonally Applied Electric and Magnetic Fields

Abstract

Anisotropic particles have been widely used to make micro/nanomotors that convert chemical, ultrasonic, electrical, or magnetic energy into mechanical energy. The moving directions of most colloidal motors are, however, difficult to control. For example, asymmetric dimers with two lobes of different sizes, ζ-potential, or chemical composition have shown rich propulsion behaviors under alternating current (AC) electric fields due to unbalanced electrohydrodynamic flow. While they always propel in a direction perpendicular to the applied electric field, their moving directions along the substrate are hard to control, limiting their applications for cargo delivery. Inspired by two separate engine and steering wheel systems in automobiles, we use orthogonally applied AC electric field and direct current (DC) magnetic field to control the dimer's speed and direction independently. To this end, we first synthesize magnetic dimers by coating dopamine-functionalized nanoparticles on geometrically asymmetric polystyrene dimers. We further characterize their static and dynamic susceptibilities by measuring the hysteresis diagram and rotation speed experimentally and comparing them with theoretical predictions. The synthesized dimers align their long axes quickly with a planar DC magnetic field, allowing us to control the particles' orientation accurately. The propulsion speed of the dimers, on the other hand, is tunable by an AC electric field applied perpendicularly to the substrate. As a result, we can direct the particle's motion with predesigned trajectories of complex shapes. Our bulk-synthesis approach has the potential to make other types of magnetically anisotropic particles. And the combination of electric and magnetic fields will help pave the way for the assembly of magnetically anisotropic particles into complex structures.

Dual-Mode-Driven Micromotor Based on Foam-like Carbon Nitride and Fe3O4 with Improved Manipulation and Photocatalytic Performance

“…In the rotating magnetic field, the rotation speed of the Fe 3 O 4 /f-C 3 N 4 motor increases as the frequency of the magnetic field increases up to 9 Hz. Due to the viscous resistance, the rotation speed declines with increasing frequency of the magnetic field at higher frequencies (Figure c) as the motor fails to follow the external magnetic field Figure d shows the snapshots of a Fe 3 O 4 /f-C 3 N 4 micromotor rotating in a rotary magnetic field of 1 Hz and 3 mT.…”

“…Due to the viscous resistance, the rotation speed declines with increasing frequency of the magnetic field at higher frequencies (Figure 5c) as the motor fails to follow the external magnetic field. 57 Figure 5d shows the snapshots of a Fe 3 O 4 /f-C 3 N 4 micromotor rotating in a rotary magnetic field of 1 Hz and 3 mT. 40,54 The mechanism for the increased reaction kinetics under a rotary magnetic field is further explored.…”

Travelling-Wave Electrophoresis, Electro-Hydrodynamics, Electro-Rotation, and Symmetry-Breaking of a Polarizable Dimer in Non-Uniform Fields

“…The special arrangement of two (dimer) or more (chain) touching spherical particles often occurs in many branches of mathematical physics and nanotechnology, such as electrostatic [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 ] and optics [ 22 , 23 , 24 , 25 ]. The tangent-sphere coordinate system can be effectively used for analytically tackling some related problems involving particle-wall interactions in various electrokinetic [ 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 ], heat transfer [ 36 , 37 , 38 ], inviscid [ 39 , 40 , 41 , 42 , 43 ], and viscous [ 44 , 45 , 46 , 47 , 48 , 49 , 50 ] flow scenarios.…”

Microrobots Powered by Concentration Polarization Electrophoresis (CPEP)

“…[9] Further, asymmetric colloidal dimers [10] and also metallo-dielectric Janus particles [11] placed on an electrode and subjected to a vertical electric field are propelled perpendicularly to the electric field in a random direction in the 2D plane defined by their current orientation. Within this setup, magnetic fields have been used in combination with ferromagnetic metallo-dielectric Janus particles [12] and ferromagnetic asymmetric colloid dimers [13] to introduce maneuverability. Further, it has been demonstrated that metallo-dielectric Janus particles can be used to transport other dielectric particles.…”

“…Within this setup, it was demonstrated that asymmetric colloidal dimers [9] and metallo-dielectric Janus particles [10] are propelled perpendicularly to the electric field in a random direction in the 2D plane. To introduce maneuverability, magnetic fields have been used in combination with ferromagnetic metallo-dielectric Janus particles [11] and ferromagnetic asymmetric colloidal dimers [12]. Further, it has been demonstrated that metallodielectric Janus particles can be used to transport other dielectric particles [11, 13, 14].…”