Microscopic visualization of heterogeneous nucleation process on smooth spherical particle: Method and results

Abstract

Heterogeneous nucleation is a very fundamental step in vapor condensation. However, it is scarcely possible to directly visualize the nucleation process because it is very quick and complicated. In present work, a method is proposed to create a mixed surface, where the hydrophilic SiO2 particle is dispersed on the super-hydrophobic substrate for a direct visualization of the nucleation process. The time-resolved images are recorded by Environmental Scanning Electron Microscopy (ESEM) system. The results indicate that only one embryo drop forms at a random point of a single particle surface and subsequently grows up and finally wraps the single particle. For multiple particles, the embryo drop occurs on the junction of particles and continues to enlarge to finally wrap all the particles. The numerical analysis shows that the nucleation ability of SiO2 is qualitatively consistent with the theoretical prediction, and quantitatively, the experimental Scr is much smaller than the predicted results.