Supported ionic liquid phases (SILPs) - ionic liquid (IL) films deposited on a high-surface-area support - are a proven strategy for catalysis, but little is known about optimising the IL for this purpose. It is easy to make new ILs and check their properties, but this is wasteful and ineffective, and it is better to tune IL properties by making mixtures, e.g. ten compounds could make 100's of mixtures. We want to understand, and hence be able to predict, how the properties of the mixtures vary with composition and we are interested in mixtures of ILs where one contains a hydrocarbon and chain and the other a fluorocarbon chain. This leads to a structuring of the liquid film which can affect how the catalyst works and we need to get to the point where we can predict how the mixture composition determines the liquid structure. Neutron scattering can answer these questions for us.