Effects of the interaction between neighboring droplets on the stability of nanoscale liquid bridges

Abstract

The mechanism of mechanical and hydraulic properties of unsaturated clays at the nanoscale hasn’t been fully understood, especially for three-phase systems. Through molecular dynamics (MD) and a series of microscopic test methods, the stability of kaolinite-water-CO2 under Dh, Sr, M∗, ds∗ and ε∗ was evaluated. The results of density field, adsorption, contact angle and capillary force of water and CO2 molecules indicated that Dh and M∗ controlled the coalescence and jumping of adjacent droplets, while the wettability of minerals depended on Sr and ε∗. When the two droplets ranged from coalescence to separation, not only the contact angle enlarged, but the capillary force declined. Although the rise of ε∗ will enhance the wettability of kaolinite, it will cause the liquid bridge to break and be adsorbed on the surface of particle in the form of a liquid film if it’s too high. In this case, contact angle of liquid bridges suddenly dropped to zero. The capillary force will also present a trend of first increasing and then decreasing. In the three-phase environment, the enlargement of Sr induced CO2 molecules to be adsorbed on the surface of solid and liquid phase due to hydrogen bonds, thereby reducing the wettability of minerals. Subsequently, capillary force became smaller. In addition, CO2 and H2O molecules at the interface were arranged in order, and the thickness of adsorption layer was from small to large: solid–gas, solid–liquid, gas–liquid. By fitting the critical conditions of liquid bridges in instability and fracture, it may be beneficial to explain macroscopic unsaturated theory and long-term experimental observations.