Microscopic visualization of interface phenomena in heterogeneous nucleation of water vapor on particles cluster

Water vapor heterogeneous condensation on nanoparticles to form droplets plays a crucial role in many fields. This process involves a complex gas-liquid-solid three-phase transition. There are two main difficulties in measuring the interface phenomenon at the microscopic level: visualization of particles nucleation and controllable condensation of water vapor. So, we proposed an in-situ observation method for controllable condensation of water vapor by constructing a mixed superhydrophobic-fine particle surface, achieving direct observation of particles nucleation by using Environmental Scanning Electron Microscopy (ESEM). The results reveal that nucleation sites are initially located at the junction of any two-close particles. Although we established a nucleation model, determining the energy barrier proved challenging through analytical expressions or definite integrals due to the complexity of finding the original function. So, we developed the code to describe the quadrature region based on Boolean operation, and solved the energy barrier for the first time by using numerical integration methods. Our results show that the critical energy barrier at the junction of two particles is only 1/37 of that on a single particle. Most notably, when water vapor condenses on complex circular and chain-shaped multi-particles, the three-fold symmetry in circled particles will firstly initiate the nucleation.