Effects of interfacial rheology on shear-induced dynamics of MXene-covered droplets

Abstract

Hypothesis: Liquid-liquid interfaces covered by nanosheets such as MXenes represent versatile building blocks for multiphase materials in many applications. Due to their high hydrophilicity, MXene nanosheets assemble at the interface only when interacting with other stabilizers such as cationic surfactants. Depending on the surfactant properties, such as the number of charged head groups, the nanosheet-surfactant interactions result in distinct interfacial network structures and interfacial rheological properties, which influence the dynamics of MXene-covered droplets. Experiments: This study uses interfacial shear and dilatational rheological techniques, such as double wall ring (DWR) rheometry and pendant drop tensiometry, to characterize the mechanical properties of the interfacial network formed by different MXene-surfactant complexes. The dynamics of single MXene-covered droplets are investigated by analyzing the deformation, breakup, and retraction behavior in a shear flow cell. Findings: Our findings suggest that the rheological properties of nanosheet-covered interfaces can be tailored by using surfactants with a different number of charged head groups, thereby changing the interfacial network structure. The interfacial network, and more in particular the interfacial shear properties in the non-linear regime, influence the dynamics of droplets under shear flow, ranging from solid-like droplets with a brittle interfacial network to droplets with an elastic interface that show a residual deformation after cessation of shear.