Controlling the Speed of Light‐Activated Colloids with a Constant, Uniform Magnetic Field

Abstract

It is demonstrated how the strength of activation for photocatalytic, self‐propelled colloids can be enhanced with a constant, uniform magnetic field. When exposed to ultraviolet light and hydrogen peroxide, the titanium dioxide‐based colloids become actively propelled. Due to the iron oxide core, a uniform field oriented perpendicular to the surface where motion takes place causes the asymmetrically shaped particles to rotate, which consequently leads to an increase in activity. The field‐dependent dynamics of self‐propulsion is quantified, and a qualitative description of how this effect arises is proposed. Since the application of the field is easily reversible, modulating the field on‐and‐off serves as a de facto “switch” that controls particle behavior.

Apparent phototaxis enabled by Brownian motion

“…21,23,26 There were no indications that variations in magnetic field strength could further improve particle guidance. Although major dependency of particle velocity on the magnetic field strength is reported for some microswimmers, 27,28 we found no significant effect in the probed Au@Ni@TiO 2 system. When the MF was reoriented in a way that the particle tracks went diagonally with respect to the light stripe, the apparent phototaxis was also observable (see ESI, † Fig.…”

Enhanced and Robust Directional Propulsion of Light-Activated Janus Micromotors by Magnetic Spinning and the Magnus Effect

“…The velocity of the light-driven spherical micromotor under electrophoretic propulsion by the photocatalytic reaction is described by the Smoluchowski equation U is the migration speed of the micromotor, ε is the fluid permittivity, ζ is the ζ potential of the micromotor surface, η is the fluid viscosity, and E is the self-built electric field which dominates the propulsion of the micromotor. Because of the opacity of Pt and TiO 2 under UV light (the self-shadow effect), , the photocatalytic reaction can only occur in the part of TiO 2 that is exposed to the incident light. In addition, the fluid that is far from micromotors remains static.…”

Magnetically locked Janus particle clusters with orientation-dependent motion in AC electric fields

“…11–15 Such micromotors can be propelled by various energy sources, including magnetic, 16–21 acoustic, 2,22–24 and electric fields, 11,25–28 as well as catalytic reactions. 29–33 As a category of electrical stimulation, induced-charge electrophoresis (ICEP) is a useful method to drive the motion of metallodielectric particles ( e.g. , dielectric particles with metal patches) in alternating current (AC) electric fields due to the highly tunable interactions between the particles and applied field.…”