Molecular Dynamics Studies of Homogeneous and Heterogeneous Thermal Bubble Nucleation

Thermal bubble nucleation was studied using molecular dynamics for both homogeneous and heterogeneous argon systems using isothermal-isobaric (NPT) and isothermal-isostress (NP_zzT) ensembles. Unlike results using NVE and NVT ensembles, no stable nanoscale bubble exists in the NPT ensembles, but instead, the whole system changes into vapor phase. In homogeneous binary systems, reducing the interaction strength between alien atoms and argon atoms significantly decreases the nucleation temperature; however, enhancing the interaction strength only increases the nucleation temperature marginally. For nanoconfined heterogeneous NP_zzT ensembles with liquid argon between two solid plates, the nucleation temperature increases as the channel height decreases if the channel height is less than ∼7.63 nm. More interestingly, in this regime, the bubble nucleation temperature could be significantly higher than the corresponding homogeneous nucleation temperature. This observation is different from the common expectation that homogeneous thermal bubble nucleation, as a result of fundamental thermodynamic instability, sets an upper limit for thermal bubble nucleation temperature under a given pressure. However, the result can be understood physically based on the more ordered arrangement of atoms, which corresponds to a higher potential energy barrier.