X-ray Reflectivity Study of the Water−Hexane Interface

Abstract

Synchrotron X-ray reflectivity is used to study the electron density profile normal to the bulk water−hexane interface. This first measurement of the microscopic interfacial width of a neat water−oil interface relied upon the development of a novel technique to flatten the liquid−liquid interface. The measurement is interpreted in terms of an error function electron density profile to yield an interfacial width of 0.33 ± 0.025 nm. Within the context of capillary wave theory, it is shown that this microscopic parameter is in agreement with macroscopic measurements of the interfacial tension. These measurements are compared to computer simulations of water−alkane interfaces.