Since the local structure of complex mixtures can show effects that are not explained by continuum models of solvents, studies such as the current one can be expected to lead to a greater understanding of solvent mixture systems. The orientation of molecules around one another, hydrogen bonding structure, and longer-range aggregation all have strong impacts on the local environment experienced by a species in a mixture. For example, conditions at the sub-nanometer scale may alter the immediate region around interfaces, catalytic sites, and minority species in solution, and have a strong bearing on the behavior of a mixture. Our novel application of double-differential pair distribution function analysis to biphasic liquids over wide ranges of composition and temperature has shown to give reproducible results, despite the weak signals, and is a powerful method for studying molecular interactions inside such complex systems. In particular, we found that, even at low water loading, DIPA-water mixtures showed signs of structuring. Whilst very careful and detailed models of solvation have been developed using diffraction methods and large-scale models on model systems, for example through the determination of partial PDFs with the use of selective deuteration, our approach of rapid measurements of entire phase diagrams, combining multiple complementary measurements, combined with modeling ideal clusters and bulk systems, can give critical insights that are difficult to extract in other ways.