Effects of Temperature and Ionic Concentration on Nanodroplet Electrocoalescence.

Abstract

Droplet electrocoalescence is of interest for various applications such as petroleum dehydration, electrospray ionization, and surface self-cleaning. Here, the effects of temperature and ionic concentration on nanodroplet electrocoalescence are investigated by molecular dynamics simulation. The results show that low ionic concentration rapidly drives ions towards water clusters and leads to dipole polarization of droplets. With an increase of ionic concentration, the particle-particle interaction is enhanced, but the mobility of free water molecules and salt ions is curbed by hydration and ion pairs, which then slows the electrocoalescence. Low temperature accelerates the rotation of water molecules but does not enhance the mobility of ions. Alternatively, high temperature not only breaks the self-assembly of water molecules along the electric field direction but also helps ions to overcome the electrostatic barrier between particles. The latter effect promotes dipole polarization to compensate for the shortcoming of less orientation polarization. The combined effects of ion concentration and temperature are investigated and unified by droplet conductivity from the microscopic point of view. The conductivity increases with the increase in temperatures and ionic concentrations. We confirm that the accurate control of droplet electrocoalescence can be achieved by a suitable combination of temperature and ionic concentration.