On the Diffuse Structure of the Toluene - Water Interface

TL;DR

This study uses X-ray reflectometry to measure the width of the toluene-water interface, revealing it is broader than theoretical predictions due to its intrinsic diffuse structure.

Contribution

It provides experimental measurements of the toluene-water interface width and compares it with theoretical capillary wave predictions, highlighting the diffuse nature of the interface.

Findings

Measured interface width is 5.7 Å, larger than the predicted 3.9 Å.

Observed broadening attributed to intrinsic diffuse structure of the interface.

Interface width is comparable to other high-molecular-weight hydrocarbon-water interfaces.

Abstract

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.