润湿性梯度和Laplace压力共同作用下的冷凝液滴自移除

It is well known that, high efficient self-removal of condensed microdroplets is very important in increasing the efficiency of cooling system and anti-icing. However, all most superhydrophobic coatings will lose low wettability under condensation condition. To explore the determinants on the transitions between Cassie condensed drops and Wenzel ones based on analyzing the relationship between the parameters of roughness structures of superhydrophobic coatings with CA, CAH, θadv, θrec, θr and Laplace pressure firstly. Then, the interface free energy of a local condensate is calculated, combined with the experimental results, the possible approaches to achieve the transition from Wenzel condensed state to Cassie case aided by roughness gradient and surface energy gradient are discussed. Finally, considering droplet nucleation requires a wettable region while droplet self-removal necessitates a superhydrophobic surface. We have combined the design of superhydrophobic surface with hydrophilic regions, enables quick nucleation, controllable coalescence, and high-efficiency self-removal of the condensed microdroplets. The relation between the wettability gradient and Laplace pressure with nucleation density, the frequency of self-propelled jumping of merged microdroplets, water condensation rates, heat transfer efficiency and anti-icing properties are explored.

针对超疏水材料在冷凝条件下易失去动态疏水性，本申请项目集实验摸索与理论分析于一体，首先，研究微纳复合表面精细结构参数与润湿性参量、Laplace压力、耐压程度间的关系，分析部分表面冷凝液滴呈Wenzel粘附态的原因，提炼促使冷凝液滴最终处于Cassie态的条件；其次，通过计算系统润湿状态转变中局部自由能变化规律，结合实验结果，探索粗糙度梯度和表面能梯度作用下冷凝液滴从凹槽中反向运动至微结构凸起处的可行性方案；最后，利用亲水区域成核势垒低，巧妙控制冷凝成核位置、提高成核密度、加速初始液斑生长，研究亲-疏水区域参数设置、表面化学成分调控与冷凝液滴合并自移除半径、频率乃至传热效率、防冰霜性能间的关系。

针对超疏水材料在冷凝条件下易失去动态疏水性，本项目集实验摸索与理论分析于一体。首先，研究了微纳复合表面精细结构参数与润湿性参量、Laplace压力、耐压程度间的关系，分析部分表面冷凝液滴呈Wenzel粘附态的原因，提炼促使冷凝液滴最终处于Cassie态的条件；其次，通过计算系统润湿状态转变中局部自由能变化规律，结合实验结果，探索了粗糙度梯度和表面能梯度作用下冷凝液滴从凹槽中反向运动至微结构凸起处的可行性方案；最后，利用亲水区域成核势垒低，巧妙控制冷凝成核位置、提高成核密度、加速初始液斑生长，研究了亲-疏水区域参数设置、表面化学成分调控与冷凝液滴合并自移除半径、频率乃至传热效率、防冰霜性能间的关系。. 项目研究成果表明，在Cu(OH)2纳米针超疏水表面，冷凝液滴会频繁的合并自移除，1-10微米范围内液滴占比维持在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；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/mm2、1000/mm2和360/mm2左右；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；通过水热法制备出了耐磨性能优异的铝基超疏水材料，经动态摩擦试验机2000次循环摩擦后，仍能维持超疏水特性且具有良好的耐酸碱腐蚀能力。冷滴液滴会在微纳米复合结构中随机生成，有益的是凹槽中的冷凝液滴在长大、合并过程中会逐渐脱离凹槽底部，最终悬浮于粗糙结构表面，证实冷凝液滴在样品表面保持Cassie态；使用自制的结冰监测系统对制备出的超疏水表面的静态和动态防冰性能进行分析，结合经典成核理论和一维传热理论，证实超疏水材料在防覆冰领域的应用前景；利用激光加工等技术，实现了各向异性或同性润湿材料的可调制备；搭建了一套材料表面覆冰强度在线测量装置及覆冰过程实时监控系统和一种集成两种特殊润湿性材料的可旋转式油水分离装置。系列成果表明，项目研究内容和目标基本实现。