Long range interactions in insulating fluids probed by SANS

The study of the microscopic interaction law represents a centraltopic in the physics of the fluid state of matter. Particular interest has been devoted in the past decades to the long-range part of the interatomic force. We review here some recent results, obtained investigating the low-q part of the static structure factor S(q) of insulating fluids, which provide a direct and unambiguous demonstration of the r-6 dispersion tail of the potential and allow an experimental determination of the strengths of the long-range double and triple dipole interactions.