The aim of this proposal is to determine the thickness of a water layer surrounding colloidal particles dispersed in oil with changes in ionic strength. Recent work by our group has indicated that this interface between the hydrophilic colloid surface and the hydrophilic head group of the surfactant can attract a thin water layer. In particular, the thickness of this water layer depends on the ionic strength of the water and valency of ions in the system. We have now succeeded in colloidally stabilising both anionic or cationic silica particles in heptane with surfactants and propose to characterise their water layers. SANS is the most direct approach to characterise these water layers. we estimate that we require 3 days beam time on LOQ, given our experience of related measurements.