梯度润湿性表面能够自主驱动液滴进行可控的定向流动,具有重要的应用价值。采用纳秒激光在304不锈钢表面加工微结构,并辅以低温热处理方法,获得了激光快速加工梯度润湿性表面。采用扫描电子显微镜、能谱分析和接触角测量仪分别观察和表征了加工表面的微结构、化学成分及接触角,采用高速相机观察液滴在梯度润湿性表面的流动状态。实验结果表明:采用激光加工后,表面C元素含量是影响表面亲疏水性的重要因素;对于304不锈钢,激光加工后通过200 ℃的短时加热,可以促进表面C元素含量发生快速变化,实现接触角的快速固化;合理设计靶材表面的微结构,可以获得具有不同接触角的均匀润湿性表面;通过合理设计表面微结构的分布,可以获得不同润湿性梯度的表面;通过改变表面微结构的分布,可以控制靶材表面液滴的流动距离和流速。

A gradient wettable surface can make a droplet autonomously flow in a pre-determined direction. Therefore, this method is important for various applications. In this study, a method is developed to quickly fabricate a gradient wettable surface on the surface of 304 stainless steel using nanosecond laser ablation and heat treatment. The surface microstructure, chemical composition, and contact angle are observed and characterized via scanning electron microscopy, energy spectrum analyzer, and contact angle measuring instrument. A high-speed CCD camera is used to observe the flow of liquid on the gradient wettable surface. The experimental results show that the content of the carbon (C) on the surface is an important factor that affects surface hydrophobicity after laser processing. For 304 stainless steel, short-time heat treatment at temperature of 200 ℃ accelerates the increase of the C content, realizing fast curing of contact angle. The uniformly wettable surfaces with different contact angles can be obtained by designing the surface microstructure of the target. Then, the surfaces with different wettability gradients can be obtained by designing the surface microstructure distribution. The flow distance and velocity of the liquid droplet on the target surface can be controlled by changing the surface microstructure distribution.