If applied under grazing incidence beam geometry (see figure 1, right panel) neutrons can offer surface sensitivity. If in addition to the specular reflectivity, off-specular scattering or the small angle scattering is collected, correlations in the plane of the interface can be analysed.

After a very brief overview of the activities at the Physics Department and the Material Physics division at Uppsala University I will focus on neutron scattering experiments probing the solid-liquid interface. Recently, it has been demonstrated that the traditionally assumed non-slip boundary condition does not always hold. The discontinuity at the interface can be quantified by a phenomenological number, the slip length (for definition see figure 1, left panel). However, the microscopic origin of slip is still not understood and different scenarios are proposed. Surface sensitive neutron scattering experiments can probe the density profile at the interface as well as lateral correlations or possibly even surface dynamics. Our recent findings, on polymers, self-assembled surfactants and simple liquids, demonstrate that slip in simple liquids can not be explained by a density depleted layer alone. The local structure and dynamics in the liquid at the interface, which are highly sensitive to the interfacial energy, have to be taken into account as well.

Contact : tellier@ill.fr