Comparative Studies of Light-Responsive Swimmers: Janus Nanorods versus Spherical Particles

The
shape of objects has a strong influence on their dynamics.
Here, we present comparative studies of two different motile objects,
spherical Ag/AgCl Janus particles and polystyrene Janus nanorods,
that move due to an ionic self-diffusiophoretic propulsion mechanism
when exposed to blue light. In this paper, we propose a method to
fabricate Janus rodlike particles with high aspect ratios and hemispherical
tip shapes. The inherent asymmetry due to the ratio between capped
and uncapped parts of the particles as well as the shape anistropy
of Janus nanorods enables imaging and quantification of rotational
dynamics. The dynamics of microswimmers are compared in terms of velocities
and diffusion coefficients. We observe that despite a small amount
of the Ag/AgCl reagent on the surface of rodlike objects, these new
Janus micromotors reveal high motility in pure water. While the velocities
of spherical particles reach 4.2 μm/s, the single rodlike swimmers
reach 1.1 μm/s, and clusters reach 1.6 μm/s. The effect
of suppressed rotational diffusion is discussed as one of the reasons
for the increased velocities. These Janus micro- and nanomotors hold
the promise for application in light-controlled propulsion transport.