There are few studies on the effect of pressure on ionic liquids; however, there are indications that, at pressures around 1.0 GPa, these systems undergo a significant change in their structure. We have examined a range of ionic liquids as a function of chain length at ambient pressure to explore the presence of microsegregated domains. Although not found at low pressure, it is possible that, as the liquid is pressurised, the domains proposed will form and an ordered structure akin to that found for the long alkyl chain length materials/liquid crystalline ionic liquids results. Neutron diffraction will be used to study the structure of 1-octyl-3-methyl imidazolium hexafluorophosphate ionic liquids as a function of pressure. In order to probe the structure and facilitate the analysis of the data obtained, selective isotopic substitution on the ionic liquid cation will be used.