An X-ray Reflectivity Study of the Water-Docosane Interface

Abstract

Synchrotron X-ray reflectivity is used to study the electron density profile normal to the interface between bulk water and bulk n-docosane (C22H46). These measurements are interpreted in terms of an error function electron density profile to yield an interfacial width of 5.7 ± 0.2 Å. In contrast with an earlier measurement on the water−hexane interface, this interfacial width disagrees sharply with the prediction from capillary wave theory, σ cap = 3.5 Å. This width can be accounted for by combining the capillary wave prediction with a contribution from intrinsic structure due to the bulk correlation length of docosane. We also discuss the absence of interfacial freezing at this interface, a phenomenon observed for n-alkanes of a similar chain length at the alkane−vapor and alkane−silicon oxide interfaces.

Transfer of non-ionic surfactants across the water-oil interface: A molecular dynamics study

“…Both theoretical and experimental studies indicate that the water-oil interfaces that are molecularly sharp (immiscible) [65], at the molecular level are actually characterized by intrinsic width of a perturbed-density layer broadened by capillary waves [66]. According to our estimates the magnitude of this separation is ca.…”

Simulations of the adsorption of ionic species at polarisable liquid∣liquid interfaces

“…In addition, the modelisation of the differential capacitance of the ITIES has been carried out using theoretical models based on ionic association [28,29], ionic penetration [30], and capillary waves [31]. Experimentally, the interfacial width and roughness of the liquidjliquid interface have been addressed by X-ray reflectivity [32][33][34] and neutron reflection measurements [33,35]. The results obtained with these techniques appear to confirm the predictions of computer simulations.…”

X-ray scattering from liquid–liquid interfaces

“…Error bars on the data are similar to the symbol size in the inset. [27,28] X-ray reflectivity data measured from the water-alkane interface for chain lengths longer than six carbons (i.e., hexane) yield interfacial widths s that are significantly larger than the value predicted by capillary wave theory (Fig. 2).…”