Wetting and evaporation of salt-water nanodroplets: A molecular dynamics investigation.

Jun Zhang,Matthew K Borg,Jason M Reese,Khellil Sefiane

doi:10.1103/physreve.92.052403

Abstract

We employ molecular dynamics simulations to study the wetting and evaporation of salt-water nanodroplets on platinum surfaces. Our results show that the contact angle of the droplets increases with the salt concentration. To verify this, a second simulation system of a thin salt-water film on a platinum surface is used to calculate the various surface tensions. We find that both the solid-liquid and liquid-vapor surface tensions increase with salt concentration and as a result these cause an increase in the contact angle. However, the evaporation rate of salt-water droplets decreases as the salt concentration increases, due to the hydration of salt ions. When the water molecules have all evaporated from the droplet, two forms of salt crystals are deposited, clump and ringlike, depending on the solid-liquid interaction strength and the evaporation rate. To form salt crystals in a ring, it is crucial that there is a pinned stage in the evaporation process, during which salt ions can move from the center to the rim of the droplets. With a stronger solid-liquid interaction strength, a slower evaporation rate, and a higher salt concentration, a complete salt crystal ring can be deposited on the surface.

Highlights

Salt water is one of the most abundant resources on this planet and we need to find ways of using it to help solve current social, health, environmental, and economic problems
This means that the evaporation rate of salt-water droplets decreases as the salt concentration increases
Our results show that the contact angle of saltwater nanodroplets increases with salt concentration

Summary

Introduction

Salt water is one of the most abundant resources on this planet and we need to find ways of using it to help solve current social, health, environmental, and economic problems. One promising opportunity is to produce fresh water from salt water using desalination technologies, such as distillation, membrane processes, and solar desalination [1,2]. Another is cooling electricity-generating equipment in the thermoelectric power industry. Salt water is well known as a cause of structural and environmental problems, such as corrosion and salt weathering [3] The latter is an erosion process that deteriorates natural stone and building materials and results from the crystallization of salt. Repeated wetting and evaporation and the resultant stresses can eventually lead to physical breakdown of the stone In both applications and problems, a fundamental fluid question is the wetting and evaporation properties of salt-water droplets

Objectives

Results

Conclusion