(43b) Pt-SiO2 Janus Particles Near the Water/Oil Interface : A Competition between Motility and Thermodynamics

The first experimental investigation of the behavior of spherical amphiphillic glass particles, i.e., Janus particles, near an oil/water interface was done by Casagrande et al. in 1989. Ever since their initial work, continued attention has been devoted to developing the field of Janus particles. In some of these studies, it was observed that these particles indicate a strong tendency of adsorbing to the oil/water interface compared to their homogeneous analogs, making Janus particles promising candidates for many applications such as emulsion stabilization, oil recovery, and cosmetics. More recently, active Janus particles have become of interest due to their behavior near interfaces ranging from investigations of the dynamics of a single particle to their self-assembly at air/water and oil/water interfaces.

Although various aspects of the behavior of Janus particles near liquid/liquid interfaces have been studied through different experimental and theoretical realizations, the effect of motility on the behavior of Janus particles near liquid/liquid interfaces has not been investigated. In our study, we demonstrate our ability to engineer the behavior of highly interfacially active Janus particles near a water/oil interface by introducing motility to the system. Passive, i.e., non-motile, platinum-capped silica (Pt-SiO2) Janus particles are fabricated using physical vapor deposition. They exhibit a strong tendency to attach to water/oil interfaces with the Pt cap facing the oil and the SiO2 side facing the water phase. In contrast, we show that active, i.e., motile Pt-SiO2 Janus particles in the presence of H₂O₂, approach the interface, orient in a sideways fashion with the Janus boundary perpendicular to the interface, and then swim in the vicinity of the interface similar to observations reported near solid/liquid interfaces.