Thermal bubble nucleation was studied using molecular dynamics for both homogeneous and heterogeneous systems using isothermal-isobaric (NPT) and isothermal-isostress (NPzzT) ensembles. Simulation results indicate that homogeneous thermal bubble nucleation is induced from cavities occurring spontaneously in the liquid when the temperature exceeds the superheat limit. In contrast to published results using NVE and NVT ensembles, no stable nanoscale bubble exists in NPT ensembles, but instead, the whole system changes into vapor phase. For a heterogeneous system composed of a nanochannel with an initial distance of 3.49 nm between the two solid plates, it is found that if the liquid-solid interaction is equal to or stronger than that between liquid argon atoms, the bubble nucleation temperature of the confined liquid argon can be higher than the corresponding homogeneous nucleation temperature, because of the more ordered arrangement of atoms within two solid walls nanometers apart. This observation is in contradiction to the common understanding that homogeneous bubble nucleation temperature sets an upper limit for thermal phase change under a given pressure. Compared to the system where the liquid-solid interaction is the same as that between liquid argon atoms, the system with reduced liquid-solid interaction possesses a significantly reduced bubble nucleation temperature, while the system with enhanced liquid-solid interaction only has a marginally increased bubble nucleation temperature.

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