The impact of droplets on solid walls is the primary behavior in spray cooling, seawater desalination, self-cleaning, and other technological processes. Based on the molecular dynamics (MD) method, the morphological evolution characteristics of nanodroplets impinging on the copper cylinder wall are studied. The effects of droplet size, initial velocity, impact position, and wall wettability on nanodroplet dynamics are analyzed. The results indicate that a single nanodroplet impacting on a nanocylinder exhibits four distinct impact modes: spread-partially wrapped-deposition (SPD), spread-completely wrapped-deposition (SCD), spread-completely wrapped-splitting-deposition (SCSD), and spreading-partially wrapped-splitting-deposition (SPSD). The trend of the influence of initial velocity and droplet size on the impact mode is similar. As the initial velocity and droplet size increase, the droplet’s kinetic energy and inertia force increase, successively exhibiting the SPD, SCD, and SCSD modes. The trend of the influence of impact position and wall wettability on the droplet impact mode is similar. When the impact eccentricity distance is small, and the wall is highly hydrophilic, it exhibits the SCD mode. With increasing impact eccentricity and enhanced wall hydrophobicity, the adhesion force between the droplet and the cylinder wall decreases, making the droplet less likely to be captured and more prone to splitting, exhibiting the SPSD mode. The change in droplet centroid height and mean square displacement could predict whether the droplet undergoes a splitting mode, and its influence is most significant at the impact position. Constrained by the cylindrical wall, the droplet impacts radially and spreads primarily in that direction. With the enhancement of wall hydrophilicity, the migration region of the three-phase contact line expands, and the droplet spreading transforms into synchronous development along the radial and axial directions. The research results can enrich the dynamic mechanism of micro-nano scale droplet impact and provide potential guidance for optimizing relevant technologies.

中文翻译：

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纳米液滴撞击圆柱壁的形态演化：分子动力学研究


液滴对固体壁的影响是喷雾冷却、海​​水淡化、自清洁和其他技术过程的主要行为。基于分子动力学（MD）方法，研究了纳米液滴撞击铜圆柱壁的形貌演化特征。分析了液滴尺寸、初始速度、撞击位置和壁润湿性对纳米液滴动力学的影响。结果表明，撞击纳米圆柱体的单个纳米液滴表现出四种不同的撞击模式：扩散部分包裹沉积（SPD）、扩散完全包裹沉积（SCD）、扩散完全包裹分裂沉积（SCSD）和铺展-部分包裹-分裂-沉积（SPSD）。初速度和液滴尺寸对撞击模式的影响趋势相似。随着初始速度和液滴尺寸的增大，液滴的动能和惯性力增大，依次表现出SPD、SCD和SCSD模式。撞击位置和壁面润湿性对液滴撞击模式的影响趋势相似。当冲击偏心距离较小且壁面高度亲水时，呈现SCD模式。随着冲击偏心率的增加和壁疏水性的增强，液滴与圆柱壁之间的粘附力减小，使得液滴不易被捕获并且更容易分裂，呈现SPSD模式。液滴质心高度和均方位移的变化可以预测液滴是否经历分裂模式，其影响在撞击位置最为显着。受圆柱形壁的约束，液滴径向撞击并主要沿该方向扩散。 随着壁亲水性的增强，三相接触线迁移区域扩大，液滴铺展转变为沿径向和轴向同步发展。研究成果可丰富微纳尺度液滴撞击的动力学机制，为优化相关技术提供潜在指导。