Bubble nucleation plays a pivotal role in microscale heat conduction, boiling heat transfer, and liquid-vapor phase change processes, because it not only governs heat transfer efficiency but also strongly regulates bubble dynamics. The nucleation processes are highly sensitive to the surface morphology and wettability of solid substrates. However, due to the inherent limitations of traditional experiments in terms of spatial resolution and observation times, revealing the microscopic mechanisms of bubble nucleation on a nanoscale remains a significant challenge—particularly under conditions involving complex surface structures and different wettability states. In this study, molecular dynamics simulations are employed to systematically investigate the mechanisms by which surface roughness and wettability influence bubble nucleation behavior on nanostructured surfaces on an atomic scale. Five copper substrates featuring sinusoidal protrusions are designed to represent different degrees of surface roughness. The sinusoidal profile, characterized by mathematical continuity and smoothness, not only facilitates the observation of bubble coalescence and contact angle evolution but also ensures comparability among models by maintaining identical protrusion height and overall width, thereby keeping the protrusion volume constant. This design allows for direct comparison of bubble growth rates and other physical quantities between different models. In addition, three different wettability conditions, namely hydrophobic, neutral, and hydrophilic, are achieved by modifying the interaction potential between oxygen and copper atoms. During the simulations, a constant heat flux is applied to the bottom copper substrate to trigger off spontaneous bubble nucleation, and local low-density regions are identified using density distribution analysis to track bubble nucleation sites; a piston-like pressure control mechanism is introduced through the top copper plate, and the displacement of this plate with time is used to quantify bubble growth rates under varying roughness and wettability. Additionally, the Kapitza resistance between solid and liquid phases is calculated to evaluate interfacial heat transfer efficiency. The results demonstrate that increasing surface roughness significantly promotes the formation of local low-density cavities, thereby accelerating the bubble nucleation and subsequent growth. As the surface wettability transitions from hydrophobic to hydrophilic, the solid–liquid interfacial thermal resistance decreases, leading to earlier bubble nucleation. Moreover, under hydrophilic conditions, the contact angle of the bubbles increases significantly, indicating enhanced detachment and growth behavior. Overall, the findings of this work advance the fundamental understanding of the microscopic mechanisms of bubble nucleation and provide theoretical guidance and technical references for designing high-efficiency heat transfer structures and tunable fluid–solid interfaces on a nanoscale.
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