Patchy Bubble‐Propelled Colloids at Interfaces

Abstract

Liquid–liquid or liquid–air interfaces provide interesting environments to study colloids and are ubiquitous in nature and industry, as well as relevant in applications involving emulsions and foams. They present a particularly intriguing environment for studying active particles that exhibit a host of phenomena not seen in passive systems. Active particles can also provide on‐demand controllability that greatly expands their use in future applications. However, research on active particles at interfaces is relatively rare compared to those at solid surfaces or in the bulk. It is studied magnetically steerable active colloids at a liquid–air interface that self‐propel by bubble production via the catalytic decomposition of chemical fuel in the liquid medium. It is investigated the bubble formation and dynamics of “patchy” colloids with a patch of catalytic coating on their surface and compare to more traditional Janus colloids with a hemispherical coating. It is found that the patchy colloids have a tendency to produce smaller bubbles and undergo smoother motion which makes them beneficial for applications such as precise micro‐manipulation. this it is demonstrated by using them to manipulate and assemble patterns of passive spheres on a substrate as well as at an air–liquid interface. It is also characterized the propulsion and bubble formation of both the Janus and patchy colloids and find that previously proposed theories are insufficient to fully describe their motion and bubble bursting mechanism. Additionally, it is observed that the colloids, which reside at the air–liquid interface, demonstrate novel interfacial positive gravitaxis toward the droplet edges, which it is attributed to a torque resulting from opposing downward and buoyant forces on the colloids.