Going with the flow: colloidal dynamics at moving immiscible fluid interfaces

A wide array of processes from contaminant transport to membrane defouling involve interactions between deposited colloidal particles and an immiscible fluid interface. Previous works have studied interactions between individual particles and a moving interface. However, in many cases, particle deposits are dense aggregates, giving rise to new complexities that cannot be described by single-particle models. We use confocal microscopy to visualize interactions between these multilayer deposits and moving immiscible fluid droplets in microchannels. As the immiscible fluid interface passes over particles, we observe that they strongly adsorb to it due to the influence of capillary forces exerted by the fluid interface as it impinges on particles. Eventually, the fluid interface becomes saturated with adsorbed particles and reaches its "carrying capacity," after which it continually sloughs off particles. While injection of immiscible fluid interfaces has been explored for its potential to remove deposited particles from solid surfaces, our study reveals that rapid saturation of the fluid interface by particles presents a shortcoming of this process. Our results show that this limitation can be overcome by increasing fluid interfacial area, thus suggesting a new approach to anti-fouling.