Orientation and surface activity of Janus particles at fluid-fluid interfaces.

Abstract

We study the influence of shape of Janus particles on their orientation and surface activity at fluid-fluid interfaces via molecular dynamics simulations. The Janus particles are characterized by two regions with different wettability divided along their major axes. Three types of Janus particles are considered: Janus spheres, Janus rods, and Janus disks. We find that Janus spheres and Janus rods prefer one orientation at the interface, regardless of the surface property. In contrast, Janus disks can adopt one of two orientations when adhered to a fluid-fluid interface: one orientation corresponds to the equilibrium state and the other is a kinetically trapped metastable state. The orientation of Janus disks strongly depends on the disk characteristics, such as their size, aspect ratio, and surface property. Furthermore, we find that changes in the shape of Janus particles strongly influence the interfacial tension at the fluid-fluid interface. According to the time evolution of the interfacial tension, the adsorption of Janus particles is characterized by three adsorption stages based on different surface activities and adsorption kinetics depending on the particle shape.