Study on trapping behaviour of SiO2-containing droplets on the solid surface

Abstract

The dynamic behaviour of droplets impacting solid surfaces exists in nature, production, and life. In this paper, for the first time, the molecular dynamics method is used to simulate capturing the behaviour of nanodroplets containing SiO2 on solid surfaces. The dynamic behaviour of nanodroplets impacting solid surfaces is analysed when the initial falling velocity v0 of the droplet is 0.3–1.5 nm·ps−1 and for different particle size ds, mass fraction φs of SiO2, and solid surfaces with various wettability. The contact angles of droplets containing SiO2 nanoparticles on the solid surface were measured, and the simulated values closely matched experimental results. The results show that the droplets on the smooth solid surface are completely captured after impact when v0 = 0.3–1.1 nm·ps−1. When v0 = 1.2–1.5 nm·ps−1, the droplet is fragmented, and the fragmentation ratio ns increases with the mass fraction φs. The droplet fragments when v0 = 1.4–1.5 nm·ps−1 on the rough solid surface when the ratio of the side length of the square column to the droplet diameter is 0.07, while the pure water droplet directly bounces and does not fragment. There is a linear relationship between the minimum height of the centre of mass and the mass fraction in the process of droplet impact. The maximum droplet’s spreading factor value in the spreading stage βmax increases with mass fraction φs and v0. When the spreading factor of droplets increases to βc ≈ 3.02, the droplet fragments. The droplet spreading presents the Wenzel state on the rough solid surface. Moreover, the pinning effect affects the droplet falling into the square column gap surface, hindering droplet spreading. Therefore, the rough surface has better catching ability for the droplet than the smooth surface, while the speed range that can be caught is larger. These results provide a theoretical basis for related engineering applications.