On the diffuse structure of the toluene-water interface

The electric density profile along the normal to the phase interface between aromatic hydrocarbon toluene and water has been studied by X-ray reflectometry using synchrotron radiation. According to the experimental data, the width of the interface under normal conditions is (3.9 $\pm$ 0.1) Å. This value is much larger than a theoretical value of (5.7 $\pm$ 0.2) Å predicted by the theory of capillary waves with an interphase tension of (36.0 $\pm$ 0.1) mN/m. The observed broadening of the interface is attributed to its own diffuse near-surface structure with a width no less than Å, which is about the value previously discussed for (high-molecular-weight saturated hydrocarbon-water) and (1,2-dichloroethane-water) interfaces.