Spherical colloids decorated with
a surface coating of catalytically
active material are capable of producing autonomous motion in fluids
by decomposing dissolved fuel molecules to generate a gaseous product,
resulting in momentum generation by bubble growth and release. Such
colloids are attractive as they are relatively simple to manufacture
compared to more complex tubular devices and have the potential to
be used for applications such as environmental remediation. However,
despite this interest, little effort has been devoted to understanding
the link between the catalyst distribution at the colloid surface
and the resulting propulsive trajectories. Here we address this by
producing colloids with well-defined distributions of catalytic activity,
which can produce motion without the requirement for the addition
of surfactant, and measure and analyze the resulting trajectories.
By applying analysis including fractal dimension and persistence length
calculations, we show that spatially confining catalytic activity
to one side of the colloid results in a significant increase in directionality,
which could be beneficial for transport applications. Using a simple
stochastic model for bubble propulsion we can reproduce the features
of the experimental data and gain insight into the way in which localizing
catalytic activity can reduce trajectory randomization. However, despite
this route to achieve trajectory control, our analysis makes it clear
that bubble-driven swimmers are subject to very rapid randomization
of direction compared to phoretic catalytic swimming devices with
equivalent geometries
