In Figure , the gray shaded region indicates where the mixture separates into water-rich and solventrich phases. Outside this region, the mixture is monophasic. In the phase-separated region, at a given temperature (e.g., 60 °C, shown in Figure with a horizontal dotted line), the DIPA-rich phase will always have the same composition regardless of the overall composition of the sample. The composition of the DIPA-rich phase is given by the intersection of the temperature tie-line (dotted line) with the phase boundary (dark gray curve). For example, for T = 60 °C, xA = 0.644. The water-rich phase has no signal in the ddG and can be neglected, since it either is not intersected by the x-ray beam, or will be subtracted during the difference process. This means that if we measure the PDFs of any nominal composition at 60 °C in the phase-separated region, we would expect to see exactly the same ddG signal in each case, that of the DIPA-rich phase with T = 60 °C, xA = 0.644. In Figure , we show the ddG signals for xA = 0.3, 0.4, and 0.5 (orange, red, and green, respectively) measured at 60 °C. Indeed, the ddGs are almost identical to each other, with broad peaks of similar amplitude at 3.7, 7.5, and 12 Å. The ddG curves are also very similar to a monophasic sample of similar composition and temperature (xA = 0.6, measured at 50 °C, Figure ). The ddG signal behaves exactly as we would expect a PDF of a molecular cluster structure, GMCS, to behave in the phase-separated region, giving further confidence that the ddG signals are intrinsic to the DIPA-water interactions in the mixture and are representative of features present in water-DIPA molecular clusters.