Small-angle x-ray scattering (SAXS) can characterize nano-scale structures in liquids. SAXS was employed in this study to assess size and shape of such structures in amine-water mixtures. SAXS experiments were performed using a Xenocs Genix 3D instrument (Sassenage, France) in medium-angle (0.02-0.07 Å -1 ), and wide-angle scattering (0.07-2.7 Å -1 ) configurations. Samples of amine-water mixtures were contained inside 1.0 mm inner diameter glass capillary tubes procured from Charles Supper, Co. (Westborough, MA, USA) and sealed with amine-compatible epoxy. A low-Q cutoff was applied to scattering data based on inspection of scattering patterns, to eliminate regions where the experimental artefact of beamstop scattering was apparent. Background correction was then performed by subtracting the scattering from an empty capillary tube. The wavelength, λ, of the incident x-ray beam was 1.54 Å. Experiments at ambient temperature were performed at 26 °C inside the instrument (i.e., without active temperature control). SAXS fitting was performed using SasView 5.0.4. A spherical model with a hard-sphere structure factor was used for all samples (details available in the Supplemental Information).