One important question is whether the molecular structures adopted by DIPA and water vary with the concentration of the mixture in the monophasic region. We plot ddG for mixtures of varying concentration (0.1 ≤ xA ≤ 0.8), all collected at T = 26 °C, in Figure . If the structure of the DIPA-water clusters does not change with composition but the number of the clusters increases, we would expect to see the same signal persist but change in amplitude with changing xA. On the other hand, if the nature of the clusters themselves changes with composition, we would see the shape of the ddG signal changing. In the measurements (Figure ) we see the same characteristic triangular peaks and valleys in the ddG as before, with broad peaks at 3.7 and 7.5 Å, that do not change shape but decrease in amplitude with increasing amine content (or, equivalently, decreasing water content). Apparently, the mixtures adopts the same molecular structures across compositions. Naively, normalizing the curves by the mole fraction of water in the mixture, xW = 1 -xA (i.e., plotting ddG/(1 -xA)), might account for the observed changes in amplitude of the ddG. The ddGs scaled in this way are shown in Figure . Except for xA = 0.1 and 0.2, the curves collapse perfectly on to each other. This is strong evidence that the MCS of DIPA and water are present and do not change significantly in nature with changing concentration for all compositions xA ≥ 0.3. The samples with xA = 0.1 and 0.2 gave significantly different signals, but we later ascertained that this was because of phase separation, resulting in the x-ray beam intersecting the aqueous phase instead of the organic phase.