Water Vapor Adsorption-Desorption Hysteresis Due to Clustering of Water on Nonporous Surfaces.

Water vapor is continuously adsorbed onto and desorbed from all kinds of surfaces depending on changes in relative humidity. Adsorption-desorption hysteresis of water that occurs on various nonporous surfaces and extends down to low relative humidities has been reported for decades, but remains unexplained. Here we show experimentally that such hysteresis is a common phenomenon on metal oxide and mineral surfaces and can be divided into two distinct categories based on the wettability of the adsorbent surface.

The molecular scale mechanism of deposition ice nucleation on silver iodide.

Heterogeneous ice nucleation is a ubiquitous process in the natural and built environment. Deposition ice nucleation, heterogeneous ice nucleation that - according to the traditional view - occurs in a subsaturated water vapor environment and in the absence of supercooled water on the solid, ice-forming surface, is among the most important ice formation processes in high-altitude cirrus and mixed-phase clouds. Despite its importance, very little is known about the mechanism of deposition ice nucleation at the microscopic level.

Computer Simulation of the Surface of Aqueous Ionic and Surfactant Solutions.

The surface of aqueous solutions of simple salts was not the main focus of scientific attention for a long while. Considerable interest in studying such systems has only emerged in the past two decades, following the pioneering finding that large halide ions, such as I, exhibit considerable surface affinity. Since then, a number of issues have been clarified; however, there are still several unresolved points (e.

Water Activity from Equilibrium Molecular Dynamics Simulations and Kirkwood-Buff Theory.

Water activity and related thermodynamic properties are calculated for several aqueous solutions using equilibrium molecular dynamics in conjunction with the recent extension of the Kirkwood-Buff (KB) theory for closed systems. The general applicability of this method is evaluated on aqueous mixtures of ethanol, glyoxal, malonic acid, and NaCl, which represent different types of condensed-phase interactions. Solution microstructures are analyzed using KB integrals and cluster analysis to identify molecular associations due to hydrophobic interactions, hydrate formation, hydrogen bonding, or electrostatic forces affecting solution nonideality in the different systems.

Molecular Structure Inhibiting Synergism in Charged Surfactant Mixtures: An Atomistic Molecular Dynamics Simulation Study.

Synergistic and nonsynergistic surfactant-water mixtures of sodium dodecyl sulfate (SDS), lauryl betaine (C12B), and cocoamidopropyl betaine (CAPB) systems are studied using molecular simulation to understand the role of interactions among headgroups, tailgroups, and water on structural and thermodynamic properties at the air-water interface. SDS is an anionic surfactant, while C12B and CAPB are zwitterionic; CAPB differs from C12B by an amide group in the tail. While the lowest surface tensions at high surface concentrations in the SDS-C12B synergistic system could not be reproduced by simulation, estimated partitioning between surface and bulk shows trends consistent with synergism.