To better understand the co-assemblies observed, we investigated the kinetics of adsorption of the two proteins alone and the architecture of the resulting interfaces via tensiometry and neutron reflectometry. The interfacial pressure of corresponding liquid-liquid interfaces increased rapidly upon adsorption of both b-casein and BSA, further confirming that both proteins adsorb rapidly in the system studied (Supplementary Figure ). In addition, although increases in interfacial shear storage moduli were slow and overall remained very modest in the case of b-casein (Figure ), the interfacial pressure rapidly and very significantly increased for this protein. This is in good agreement with the evolution of surface pressures previously reported for b-casein at other oil or air interfaces .