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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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Keywords:
- molecular dynamics /
- bubble /
- roughness /
- wetting condition
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图 1 模拟系统结构 (a) 整体结构图; (b) 不同模型基底结构投影图; (c) 基底中Cu原子的功能分层示意图
Figure 1. Structure of the simulation system: (a) Overall structure diagram; (b) projection diagrams of substrate structures for different models; (c) schematic diagram of functional layering of Cu atoms in the substrate.
图 2 模拟系统在中性润湿条件下的气泡成核快照 (a) 模型#1; (b) 模型#3; (c) 模型#5
Figure 2. Snapshots of bubble nucleation under neutral wetting condition in simulation systems: (a) Model #1; (b) Model #3; (c) Model #5.
图 3 密度统计区域示意图
Figure 3. Schematic diagram of the density statistical region.
图 4 各模型统计区域内H2O分子数密度随时间的变化图
Figure 4. Number density variation of H2O molecules over time in the statistical region for each model.
图 5 各模型顶部铜板位移随时间变化图 (a)模型#5, 0.21 ns; (b)模型#5, 0.5 ns; (c)模型#5, 0.61 ns
Figure 5. Time evolution of the top Cu plate displacement for each model: (a) Model #5, 0.21 ns; (b) Model #5, 0.5 ns; (c) Model #5, 0.61 ns.
图 6 各模型顶部Cu板高度相同时的密度分布图 (a) 模型#1, 0.75 ns; (b) 模型#3, 0.65 ns; (c) 模型#5, 0.54 ns
Figure 6. Density distribution maps of each model at the same top Cu plate height: (a) Model#1, 0.75 ns; (b) Model #3, 0.65 ns; (c) Model #5, 0.54 ns.
图 7 0.5 ns时刻模型1#温度分布图
Figure 7. Temperature distribution of model #1 at 0.5 ns.
图 8 统计区域内各模型H2O的温度随时间的变化
Figure 8. Temperature variation of H2O in the statistical region over time for each model.
图 9 模型#1和#5在不同润湿条件下的气泡成核快照 模型#1: (a) 疏水条件; (b) 中性条件; (c) 亲水条件 模型#5: (d) 疏水条件; (e) 中性条件; (f) 亲水条件
Figure 9. Snapshots of bubble nucleation in Model #1 and #5 under different wettability conditions. Model #1: (a) Hydrophobic condition; (b) neutral condition; (c) hydrophilic condition. Model #5: (d) Hydrophobic condition; (e) neutral condition; (f) hydrophilic condition.
图 10 模型#1和#5在不同润湿条件下统计区域内H2O分子数密度随时间的变化图
Figure 10. Temporal evolution of H2O molecular number density in the sampling region for Model #1 and #5 with different wettability conditions.
图 11 模型#1在不同润湿条件下气泡成核时刻的密度分布图 (a) 疏水条件, 1.12 ns; (b) 中性条件, 0.77 ns; (c) 亲水条件, #0.67 ns
Figure 11. Density distribution diagram at the moment of bubble nucleation in Model #1 under different wettability conditions: (a) Hydrophobic condition, 1.12 ns; (b) neutral condition, 0.77 ns; (c) hydrophilic condition, 0.67 ns.
图 12 模型#1在不同润湿条件下气泡接触角随时间变化图
Figure 12. Temporal evolution of bubble contact angle for Model #1 under different wettability conditions.
图 13 模型#1和#5在不同润湿条件下顶板的位移随时间的变化图
Figure 13. Displacement of the top copper plate over time in model #1 and #5 under different wettability conditions.
图 14 模型#1和#5在不同润湿条件下统计区域内H2O的温度随时间的变化图
Figure 14. Temperature variation of H2O in the sampling region over time for model #1 and #5 under different wettability conditions.
图 15 模型#1和#5在不同润湿条件下的Kapitza热阻随时间的变化图
Figure 15. Variation of Kapitza resistance over time for model #1 and #5 under different wettability conditions.
图 16 不同粗糙度和润湿条件下的稳定气泡形成时间
Figure 16. Stable bubble formation time under different roughness and wetting conditions.
表 1 L-J势函数参数
Table 1. L-J potential parameters.
Atom pairs σ/nm ε/meV Cu—Cu 0.2377 409.300 O—O 0.3166 6.739 O—Cu (疏水) 0.3380 3.685 O—Cu (中性) 0.3190 7.370 O—Cu (亲水) 0.3011 14.740 
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表 2 各模型的表面粗糙度
Table 2. The surface roughness of each model.
模型 #1 #2 #3 #4 #5 粗糙度 1.04 1.16 1.32 1.49 1.67
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