To further investigate molecular dynamics within protein assemblies at liquid interfaces, we carried out FRAP experiments on oil droplets stabilised by corresponding protein layers (Figure ). Labelled proteins were assembled at the surface of droplets, followed by photobleaching of defined areas. Recovery of the fluorescence intensity was then monitored for at least 2 min. In contrast to quasi-2D protein assemblies that significantly recover intensities in biological systems, such as in focal adhesions within the same time frame , almost no recovery was observed for BSA and b-casein interfaces (Figure ). A very low level of recovery was initially observed in b-casein assemblies, but this reached a plateau at approximately 5% of the initial fluorescence (Figure ). BSA displayed negligible evidence of any recovery processes. This result was surprising, as we expected higher levels of fluidity and molecular diffusion at corresponding interfaces in the case of b-casein, based on the lack of changes in interfacial shear moduli observed (Figure ). However, b-casein is known to form assemblies even in solution, upon association with Ca 2+ PO4 3-species, with average diameters of 150 nm, corresponding to objects with molecular weights near 100 MDa . Therefore, casein assembly at liquid-liquid interfaces, although forming relatively fluid interfaces with aggregates not coupled with each other from a mechanical point of view, does not display significant molecular diffusion at the timescales studied.