Abstract: The spread behaviors of the underwater oil droplet on smooth brass substrate were studied using high⁃speed microscopic imaging technology. Chemical and physical modifications were made on the surface of the brass sheet to change its surface properties, and the controllable regulation of superoleophilic–superoleophobic wettability gradient of the surface was achieved successfully. The spreading length and contact angle of the oil droplet rising to different modified surfaces were tested. Different from that in air condition, influence of water surrounding the oil droplet must be considered, which is complicated in water. In this work, on the basis of the energy conservation mechanism, quantitative relationship among the eigenvalues for the spreading behaviors of the oil droplet rising to the surfaces, such as droplet dimensionless spreading length, the droplet impact velocity, droplet size, droplet properties, viscosity of the water and surface wettability, were obtained. An optimized spreading dynamic model was constructed to describe the spreading behaviors of underwater oil droplets on surfaces with different wetting properties, to give support for the design of new oil⁃water separation equipment.

Key words: Oil?water separation, Droplets spreading, Special wettability, Energy analysis

摘要： 通过高速显微实验与理论推导相结合的方式，从微观角度研究了水中油滴在光滑铜板基底的铺展行为；通过物理和化学修饰，实现了黄铜表面水下超亲油到超疏油的可控调节，观察了油滴浮升到修饰黄铜表面后铺展长度随时间变化的差异。与空气中液滴撞壁铺展不同，水中油滴的铺展需要同时考虑液滴铺展过程中周围流体对液滴铺展的黏性作用，其在基底表面的铺展过程十分复杂。采用能量守恒方法，得到了油滴在水中基底表面上的特征值之间的定量关系，建立了基于能量守恒方法的油滴在不同润湿性固体基底表面的铺展模型，用以指导新型油水分离设备的制备。

关键词: 油水分离, 液滴铺展, 表面润湿性, 能量分析