Tuning interfacial rheology and particle microstructure with Janus particles

Particle-laden fluid interfaces are ubiquitous in nature and have attracted considerable research interest, due to their exceptional ability to stabilize interface-rich materials such as emulsions, foams and cocontinuous blends. Here, we explore the effect of a small amount of additive on the interfacial rheology and the microscopic structure of such an interface. Using a custom-built interfacial stress rheometer, we show that the addition of a small amount of platinum-polystyrene (Pt-PS) Janus particles (1:40 ratio of Janus versus PS) within a monolayer of PS colloids can lead to more than an order-of-magnitude increase in the surface modulus of the monolayer with enhanced elasticity, greatly improving the stability of the interface. This drastic change in interfacial rheology is associated with the formation of local particle clusters surrounding each Janus particle. We further develop a simple model based on interparticle interactions, which qualitatively explains the origin of local particle clusters and the increase of the interfacial elasticity. Our systematic experiments demonstrate a new way to tune the microstructure and stability of particle-laden fluid interfaces.