Dynamics and rheology of 2D particles at fluid–fluid interfaces

Two-dimensional (2D) particles can be confined to a fluid–fluid interface to create a rheologically-complex interface with dynamic particle–particle and particle–membrane interactions that are still poorly understood. There are dozens of bulk materials from which 2D particles can be made, including graphene, graphene oxide, hexagonal boron nitride, molybdenum disulfide, and MXenes, and there is interest in utilizing them because of the unique properties they have over their bulk counterparts. Increasing use of 2D materials in consumer products and novel materials science applications such as Pickering emulsions, composite foams, and films, adds urgency to improve our understanding of how the atomically thin nature and variable chemistry of 2D particles makes their dynamics and interfacial rheological properties at fluid–fluid interfaces different than spheroidal particles. This short review highlights key advances that have been made in understanding the dynamics of 2D particles at fluid–fluid interfaces, including in interfacial rheology and particle–particle dynamics, and it includes discussion on important future research directions. • Atomic-scale thickness of 2D particles makes their behavior at fluid–fluid interfaces different than spheroidal particles. • Surface area concentration of 2D particles determines the relevant interfacial dynamics. • Despite demonstrated applications of 2D particles at fluid–fluid interfaces, little is known about film morphology. • Interfacial rheological measurements have been made on few 2D particle systems, but more are needed.