(111b) Active Janus Particle Behavior at Oil/Water Boundaries

Janus particles (JP) are asymmetrical particles with each hemisphere having a unique surface composition. The JP in focus is a silica particle with a smooth platinum (Pt) cap on one side. When placed in an aqueous solution of hydrogen peroxide (H2O2), the Pt reacts with the H2O2 and produces water and oxygen on one side of the particle, propelling it forward in the opposite direction. This JP is active without the presence of a magnetic, electric or acoustic field, making it an autonomous swimmer with a chemical motor. Micromotors have become of recent interest of researchers and industry professionals for applications in drug delivery, wastewater treatment and sensors.

JPs are fabricated by depositing Pt on top of silica monolayers in a physical vapor deposition machine (PVD). During the deposition, the Pt is deposited normal to the surface of the silica particles. The top half of the silica particles shield the bottom half of the silica particles leaving the top half Pt and the other half silica. The Pt surface and silica surface have different wettability properties making the JPs amphiphilic.

An observation cell was designed to observe JP behavior at an oil/water boundary. A hexadecane droplet was placed on the bottom of a swimming basin of JP and water. From a top view, the oil/water boundary was clearly defined, and the JPs interaction with the boundary could be observed. The oil phase and water phase lay next to each other on the same X-Y plane, so gravity in the Z direction does not affect the JP’s interaction with either phase.

Here we are reporting on the behavior of JPs at an oil/water boundary including the JP position at the oil/water boundary, the guidance of active JPs along the perimeter of the oil droplet, and the effect of JP activity on the JP interactions with the oil/water boundary. Having a greater understanding of the behavior of micromotors in a variety of environments will supply the knowledge needed to engineer guided JP systems.