超疏水材料表面冷凝液滴自移除及液滴尺寸分布规律

Self-propelled and Size Distribution of Condensate Droplets on Superhydrophobic Surfaces

目的优化电化学沉积法制备氢氧化铜纳米结构的实验参数,探究不同润湿性表面冷凝液滴尺寸分布规律。方法采用正交试验法,综合考虑电解液浓度、反应温度、极化时间、电流密度对接触角的影响,并通过SEM分析其表面形貌。同时,基于MATLAB软件,提出一种能快速精确识别、提取并统计冷凝液滴特征值的图像处理方法。结果正交试验最优参数为浓度0.5mol/L、温度5℃、时间2000s、电流密度4 mA/cm^2,此时样品表面接触角高达168.8°,滚动角小于3°。冷凝实验结果显示,在超疏水表面,冷凝液滴会频繁的合并自移除,液滴平均粒径最小,粒径在1~10μm范围内的液滴占比维持在50%左右;而在疏水与亲水样表面,冷凝液滴仅能发生合并现象,液滴平均粒径显著增大;冷凝后期,超疏水、疏水与亲水样表面冷凝液滴密度分别稳定在2000、1000、360 mm-2左右。结论纳米针结构能最大限度地降低固液接触面积,降低冷凝液滴粘附力,提高冷凝液滴合并自移除频率,减少冷凝液滴直径,提高冷凝液滴更新率,有望实现高效冷凝传热。同时通过与Image-J图像处理结果比对,验证了该冷凝液滴尺寸分布图像处理方法的可行性。

The work aim to optimize the experimental parameters of preparing copper hydroxide nanostructures by electrochemical deposition and to explore the size distribution of condensate droplets on different wettability surfaces.Orthogonal test method was adopted to comprehensively consider the influence of electrolyte concentration,reaction temperature,polarization time and current density on contact angle,and its surface morphology was analyzed by SEM.At the same time,a method to quickly and accurately identify,extract and count the characteristic value of condensate droplets was proposed based on MATLAB programming software.The optimal parameters of the orthogonal test were concentration 0.5 mol/L,temperature 5℃,time 2000 s,current density 4 mA/cm^2.Under this condition,the contact angle of the sample was up to 168.8°and the sliding angle was less than 3°.The condensation test results shown that on the superhydrophobic surface,condensate droplets can coalescence and self-propelled frequently.The average diameter of droplets was the smallest,and the proportion of droplets in the range of 1~10μm remained at about 50%.On the hydrophobic and hydrophilic surfaces,condensation droplets can only merge,and the average diameter of droplets increased significantly.And the condensate droplet density on the superhydrophobic,hydrophobic and hydrophilic surfaces was stable at about 2000 mm-2,1000 mm-2 and 360 mm-2 respectively,finally.We found that the nano-needle structure can minimize the solid-liquid contact area,reduce the adhesive force of condensate droplets,improve the condensate self-propelled frequency,reduce the diameter of condensate droplets,and improve the update frequency of condensate droplet,which is expected to achieve efficient condensation heat transfer.At the same time,the feasibility of the image processing method for the size distribution of condensing droplets is verified by comparison with the image-J processing results.