This proposal aims to extend our understanding of ionic liquid structure and determine the effect of a short and long alkyl chain length ionic liquid on the nanoscale segregation within the liquid structure. Any changes to this property will have significant effects on not only the ionic liquid¿s physical properties but also the tunability of the ionic liquid to undertake selective reactions whereby different reagents/functional groups will be solvated by different parts of the ionic liquid. Neutron diffraction will be used to study the structure of combinations of 1-ethyl-3-methyl imidazolium and 1-octyl-3-methyl imidazolium hexafluorophosphate ionic liquids as a function of composition. 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.