Investigation of the dew condensation and subsequent spontaneous jumping of droplets on the highly hydrophobic surface under cooling

以勃姆石和疏水硅烷为原料，制备了具有纳米级随机粗糙结构的超疏水涂层。采用Peltier冷却元件对试样进行冷却，并利用高速摄像系统从两个不同方向观察到由结露在涂层上形成的水滴的自发跳跃。水滴的自发跳跃发生在两个以上水滴的合并、变形和形状恢复之后。小的跳跃液滴具有较大的初始跳跃速度。初始跳跃速度随聚并前液滴尺寸差的增大而减小。实际跳跃速度小于理论值。当样品在30度下降时，水滴跳跃频率随冷却时间重复增加-减少的循环，并保持水滴去除性能。外加电场能显著提高水滴的跳跃高度。

Superhydrophobic coatings with nano-scale random roughness structure were prepared using boehmite and hydrophobic silanes. The samples were cooled by Peltier cooling element, and spontaneous jumping of water droplets formed on the coatings by dew condensation was observed from two different directions using high-speed camera systems. Spontaneous jumping of water droplets occurred subsequent to coalescence of more than two water droplets, deformation, and shape recovery. Small jumping droplets exhibited great initial jumping velocity. Initial jumping velocity decreased with increasing the difference in droplet sizes before coalescence. Actual jumping velocity was smaller than the theoretical value. When the sample was declined at 30 degrees, jumping frequency of water droplets repeated the increasing-decreasing cycle against cooling time and sustained droplet removal property. The jumping height of water droplets was remarkably increased under an external electric field.