(720e) Janus Particles and Liquid Interfaces: Approach, Breach and Flow Behavior

One fascinating characteristic of colloidal particles involves their binding to liquid interfaces, which results in a substantial desorption energy that can be harnessed to stabilize the interface. Nevertheless, to render an interface stable, proper wettability and suitable surface properties are essential. In particular, tuning the amphiphilicity of colloidal particles is believed to significantly impact their interaction with interfaces provided that upon adsorption Janus particles possess the right orientation toward the preferred phase. Dynamics of such colloidal particles moving towards and onto an interface is therefore of considerable interest. Using molecular dynamics simulations and digital holography microscopy, we have monitored the translational and rotational motion of nano- and micron-sized Janus particles approaching and binding to an interface, respectively. Based on our study, Janus particles demonstrate strong orientation both before and after breaching. More specifically, the interfacially trapped particles remain for long periods of time in a specific angular orientation, which is not necessarily the upright configuration. 

In addition to binding dynamics and interfacial configuration of colloidal particles, the flow behavior of colloidal monolayers formed at the interface contributes to stability. For instance, higher stability of Pickering emulsions is believed to stem from the viscoelasticity of the particle-laden interfaces. However, little is known about the impact of particle amphiphilicity on the flow behavior of particle-laden interfaces and even less information is available linking the rheological measurements to studies on emulsion stability. We have investigated the flow behavior of interfaces decorated with colloidal particles to examine the impact of particle wettability and amphiphilicity on the viscoelastic nature of these interfacial films manifested by the dynamic surface modulus.

The study is aimed to shed light on the significance of the colloidal particle amphiphilicty during particle adsorption and its impact on the interfacial rheology with the ultimate goal to relate all these aspects to emulsion stability.