The spontaneous selfassembly of nanoparticles (NP) at liquid-liquid interfaces is a phenomenon present in nature and relevant for many applications, such as, emulsion technology, nanostructured materials, nanoencapsulation, separative processes, food technologies, etc. The driving force for NP self-assembly at a liquid interface is their amphiphilic character, but NPs often lack this feature. In order to exploit such phenomena in applications, the adsorption of suitable surfactants at the NP surface is particularly attractive. We propose to use neutron reflectivity to study the structure of these mixed NP-surfactant at the oil/water IF to achieve a detailed control of their properties and functionality in applications. One can expect significant differences in the re-arrangement of the surfactant within the layer,which in turn influences the macroscopic equilibrium and kinetic features.