Structural characterization of water/tert-butanol mixtures by small-angle x-ray scattering

Water/alcohol mixtures have attracted much attention due to their peculiar properties. In this work we focus on the system containing tert-butanol and water. The aim is to determine the structure of the liquid as a function of the alcohol concentration, as it might be related to the mixture properties. Small-Angle X-ray Scattering (SAXS) was used in the structure characterization. SAXS curves were obtained for mixtures with different tert-butanol/water molar ratios at room temperature. From the absolute scaled curves, the radius of gyration of the local aggregates and extrapolation to zero angle intensity were obtained. The aggregates’ size increases with tert-butanol concentration, reaching a maximum at intermediate concentration and then decreases when more tert-butanol was added. A model developed by D`Arrigo and Teixeira was used to analyze the curves. The results showed that water-rich aggregates are present, forming clathrates. The clathrates increase when tert-butanol is added at small concentration, reach a maximum size, but when the relative amount of water in the mixture decreases, they break into smaller aggregates immersed in a medium formed mainly by tert-butanol.