In the range 0.2 < xA < 0.5, a low-Q plateau emerges. Its intensity increases with increasing water fraction. All these SAXS curves have a "knee" located at around 0.2 Å -1 , suggesting that the water-DIPA nanophase-separation is present as nanoscale objects of a quite well-defined size in the DIPA-water mixture. These SAXS curves were best fitted by a model of polydisperse spheres, with a hard sphere structure factor. This fit returns an average spherical radius parameter, rfitted, and a volume fraction parameter, φfitted, representing the volume fraction of the mixture occupied by the spheres. The fitting results are detailed in Table of the Supplemental Information, and the best-fit curves are shown as black lines in Figure .