Richard Archer1 Andrew Parnell1 Andrew Campbell1 Jonathan Howse1 Stephen Ebbens1

1, The University of Sheffield, Sheffield, , United Kingdom

Micron scale active Janus colloids produce propulsive motion at low Reynolds numbers by employing asymmetric catalytic decomposition of dissolved ‘fuels’. Many applications have been proposed for small scale motile devices such as drug delivery within the body, and mass transport in microfluidic devices.
A current limitation to practical use is the low yielding fabrication methods employed, typically involving physical vapour deposition (PVD) to deposit a thin layer of platinum catalyst. PVD is limited by its line of sight nature to planar coatings and defects arising from colloids shadowing close contact neighbours limits the packing density of the colloids and therefore the resulting yield.
Here we describe a scalable, solution based synthesis to producing large quantities of catalytic Janus colloids by the seeding and growth of the platinum metal catalyst, utilising a Pickering emulsion technique to control the asymmetric catalyst distribution.
We compare the morphology and phoretic motion between the solution based method and the traditional PVD prepared Janus colloids. Our results indicate that the solution based synthesis produces active Janus colloids with comparable propulsive velocities and trajectories to the traditionally prepared active colloids by PVD in aqueous solutions of hydrogen peroxide and is therefore a viable synthetic route. Importantly the solution based method can be easily scaled to produce gram scale quantities of active Janus colloids.
Our results also indicate that morphological differences between the two metal deposition results in less platinum being required to produce equivalent propulsion for the solution prepared active colloids.
Finally we discuss the potential for the solution based synthesis to enable coatings of alternate metal oxide catalysts which are difficult to deposit through PVD.