To investigate whether crosslinking of b-casein interfaces could allow recovering the interfacial mechanics of BSA assemblies, time sweep experiments were followed by a complete removal of the free proteins from solutions, using a continuous flow of PBS, and injection of the heterobisfunctional crosslinker sulfo-SMCC (Figure ). Throughout the washing step, we observed an excellent maintenance of the mechanical properties of the BSA interfaces generated (b-casein interfaces not displaying significant changes in interfacial shear moduli compared to pristine liquid-liquid interfaces, eventual changes occurring during washing could not be directly evidenced). Upon introduction of sulfo-SMCC, a steady increase in interfacial mechanics was observed, for both proteins, resulting in sulfo-SMCC crosslinked b-casein interfaces displaying comparable moduli to those based on BSA. In addition, interfacial stress relaxation profiles were also comparable for both crosslinked BSA and b-casein assemblies, further demonstrating that, at the protein densities achieved, effective crosslinking can be obtained in both cases. Similarly, BSA and b-casein protein nanosheets formed at Novec 7500 interfaces in the presence of pentafluorobenzoyl chloride (previously shown to mediate physical crosslinking of albumin and b-lactoglobulin assemblies ) resulted in significantly stiffer interfaces with significant levels of elasticity (Supplementary Figure ). Having explored the impact of the composition of mixed protein assemblies on interfacial dynamics and mechanics, we then investigated the thermodynamic stability of protein layers in response to protein exchange. Indeed, such phenomena have important implications on emulsion stability and the stability and mechanical properties of protein-based interfaces. The evolution of interfacial mechanics during exchange experiments was first examined. After formation of monoprotein assemblies at oil-water interfaces, the excess free protein was washed as detailed above and the second protein was introduced in the aqueous (PBS) phase, at a concentration of 1 mg/mL.