非对称微沟槽表面液滴各向异性润湿行为研究

ANISOTROPIC WETTING BEHAVIORS OF DROPLETS ON THE SURFACE OF ASYMMETRICAL MICROGROOVES

液滴在各向异性表面的润湿行为对于液滴操作和运动控制具有重要的科研与工程价值.采用重力式测试系统对非对称沟槽表面上液滴各向异性润湿行为进行表征,分析了沟槽几何结构非对称性、沟槽高度和宽度以及浸油处理对液滴静润湿与动润湿行为的影响规律.结果表明,沟槽几何结构不对称性会影响液滴润湿状态,液滴在非对称沟槽表面不同方向上接触角差异比对称沟槽更大,使得各向异性更显著;浸油处理会减小沟槽表面液滴接触角,从而表现出更明显的各向异性;非对称沟槽表面的接触角随沟槽高度增大而减小,随宽度增大而增大,表面浸油处理会缩小试件间接触角的差异,高度和宽度对浸油处理后的非对称表面的调控作用基本失效;当沟槽宽度增加时,浸油处理后的非对称沟槽表面滑动角减小,同时液滴沿非对称沟槽大顶角向小顶角方向运动时的滑动角大于沿反方向运动时的滑动角,且液滴体积越大,滑动角越小.最后,对上述规律进行了接触线理论分析,并从表面能模型角度推导出滑动角理论公式,与实验结果基本吻合.

The wetting behaviors of droplets on anisotropic surface have importantly scientific research and engineering value for the control of droplet operation and movement.In the paper,a gravity test system is used to characterize the anisotropic wetting behaviors of droplets on the surface of asymmetric grooves,and the effects of groove geometry asymmetry,groove height and width,and oil immersion treatment on droplet static and dynamic wetting behaviors are studied.The results indicate that geometric asymmetry of the groove affects the wetting state of the droplet,and the difference of the contact angle of the droplet in different directions on the surface of the asymmetric groove is greater than that in the symmetrical groove,so the anisotropy of the asymmetric groove surface is more significant than that of the symmetric groove surface.The contact angle of droplets on grooves surface with oil immersion treatment decreases,resulting in more significant anisotropy than that in the non-oil immersion state.The contact angle of the asymmetric groove surface decreases with the increase of the groove height h,and increases with the increase of the width c.The regulation effect of height and width on the asymmetric surface after oil immersion is basically ineffective with the same contact angle anisotropy characteristics in different specimens basically due to the difference of contact angle among specimens reduced by surface oil immersion treatment.When the width of the groove increases,the sliding angle of the surface of the asymmetric grooves decreases.At the same time,the sliding angle of the droplet moving along the direction of the asymmetric groove from the large top angle to the small top angle is larger than that in the opposite direction,and the larger the droplet volume,the smaller the sliding angle.Finally,the above laws are analyzed by contact line theory,and the slip angle theory formula is derived from the surface energy model,which is basically consistent with the experimental results.