Molecular Arrangement and Surface Tension of Alcohol Solutions

Abstract

This study investigated the relationship between molecular arrangement and surface tension of water mixtures with methanol and ethanol. It has been found that the molecular structure of interfacial zone was deterministically correlated to alcohol concentration. From the water dipole moment, an interfacial boundary was defined. The boundary then was used to calculate the water and alcohols in the interfacial zone, which was then used to calculate the surface tension. The prediction from simulated data closely followed the experimental data. The analysis revives the relevance of the molecular arrangement, which had been the main focus in the early 20th century, in quantification of surface energy. The results can supplement the current thermodynamic analysis to correctly predict the surface adsorption.

Surface properties of the ethanol/water mixture: Thickness and composition

“…To further verify the consistency of the simulations, the surface tension reduction at each concentration was compared with experimental data [6], as shown in Figure 4. It can be seen that the simulated values were consistent with experimental values, and similar to previous reports [36,37].…”

Adsorption of sodium iodine at air/water interface

“…It should be noted that a newly-defined interfacial limited has been successfully applied to the systems of alcohols aqueous solutions [29], alcohols/NaCl mixture [30] and NaCl solution [14] to quantify the molecular arrangement of the adsorption zone. Most importantly, this limiting plane of interfacial zone helps verify the positive net ionic adsorption at the air/water interface of NaCl solution, which is in contrast to traditional understanding of a negative adsorption at air/liquid interface [15,31], where ions are expected to be depleted from the surface due to the less polarization of outmost interfacial water layer [32].…”

Surface Potential of the Air/Water Interface

“…The exact position of this plane was found by fitting the profile of the dipole water moment against a polynomial function. It is worth noting that the presence of non-ionic surfactants 69 disrupted the well-structured arrangement of the interface, and shifted the positive peak further outside in response to increasing the surfactant s concentration. More importantly, the new limit allows quantitative models of the surface potential.…”