Neutron reflection from wet interfaces

Neutron reflection is one of the few newly developed techniques capable of probing structure at wet surfaces, i.e. air/liquid, solid/liquid and liquid/liquid interfaces. Although neutron scattering is not intrinsically sensitive to surfaces, the grazing incidence geometry of neutron reflection and the possibility of varying neutron refractive indices by isotopic substitution, particularly H/D substitution, make reflection extremely sensitive to selected parts of many interfacial layers. The technique is able to probe the average structure along the surface normal in a number of situations where the layer is too disordered or complex to be investigated by other methods. The application of neutron reflection to small molecules, surfactants, polymers and polymer-surfactant mixtures at the air/water interface, and examples of the behaviour of surfactants, proteins and polymers at the buried solid/liquid interface are described. Where appropriate the scope of neutron reflection relative to other new techniques is assessed.