Glancing angle metal evaporation synthesis of catalytic swimming Janus colloids with well defined angular velocity

Abstract

The ability to control the degree of spin, or rotational velocity, for catalytic swimming devices opens up the potential to access well defined spiralling trajectories, enhance cargo binding rate, and realise theoretically proposed behaviour such as chiral diffusion. Here we assess the potential to impart a well-defined spin to individual catalytic Janus swimmers by using glancing angle metal evaporation onto a colloidal crystal to break the symmetry of the catalytic patch due to shadowing by neighbouring colloids. Using this approach we demonstrate a well-defined relationship between the glancing angle and the ratio of rotational to translational velocity. This allows batches of colloids with well-defined spin rates in the range 0.25 to 2.5 Hz to be produced. With reference to the shape and thickness variations across the catalytically active shapes, and their propulsion mechanism we discuss the factors that can lead to the observed variations in rotational propulsion.

A Pickering Emulsion Route to Swimming Active Janus Colloids

“…In both cases, τ R is close to the theoretical value (1.01 s at 21 °C), at low velocities but decreases with higher velocities. However, no evidence for regular spiraling behavior was seen in the trajectories or MSD plots, suggesting that the colloids were not producing a constant propulsive angular velocity vector, as is the case for PVD prepared Janus colloids with deliberately rotationally asymmetric catalytic activity 37. When a similar phenomenon was initially observed for PVD active colloids it was suggested to be caused by surface imperfections in the active cap.…”

Helical paths, gravitaxis, and separation phenomena for mass-anisotropic self-propelling colloids: Experiment versus theory

“…However, it has been shown that self-propulsive Janus colloids often produce rotational propulsion in addition to translations. Such a rotational propulsion can be due to an accidental or engineered-in asymmetry of the platinum cap 12,23 and is also observed in self-assembled agglomerates of self-propelled colloids. 24 The 3D trajectories of massanisotropic colloids with both translational and rotational self-propulsion have not yet been considered and can be expected to be complex, as three different factors can now affect device orientation: self-propulsive rotations, a gravitational torque due to an anisotropic mass distribution, and stochastic Brownian rotations.…”

Reactive Inkjet Printing of Biocompatible Enzyme Powered Silk Micro‐Rockets

“…However, patterning platinum to produce useful directed motion requires access to vacuum evaporation equipment. [ 3,13 ] In other examples, where enzymatic catalysts have been investigated, such as catalase, which also performs rapid peroxide decomposition, these have often been bound to evaporated metals using time-consuming chemical functionalization steps. [14][15][16] Devices that perform functions such as attaching cargo, [ 6 ] require additional spatially well-defi ned chemical functionalization, distributed so as not to interfere with the catalytic activity responsible for generating motion.…”