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 (5.7 +/- 0.2) Angstrom. This value is much larger than a theoretical value of (3.9 +/- 0.1) Angstrom predicted by the theory of capillary waves with an interphase tension of (36.0 +/- 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 4 Angstroms, which is about the value previously discussed for high-molecular-weight n-alkane - water and 1,2-dichloroethane - water interfaces.