Droplet Motion on Designed Microtextured Superhydrophobic Surfaces with Tunable Wettability
Droplet Motion on Designed Microtextured Superhydrophobic Surfaces with Tunable Wettability
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DOI：
10.1021/la802033q
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发表时间：
2008-10-21
期刊：
影响因子：
3.9
通讯作者：
Qiao, Guanjun
中科院分区：
文献类型：
--
作者：
Fang, Guoping;Li, Wen;Qiao, Guanjun
超疏水表面由于其疏水性和低摩擦性能在过去的十年中在微流体系统中显示出有前途的应用。最近，设计的微结构已被实验应用于构建润湿性梯度和直接液滴运动。然而，热力学机制，负责这种规则的粗糙表面上的液滴运动还没有得到很好的理解，使得目前具体的指导方针，可调的超疏水表面的设计是不可用的。在这项研究中，我们提出了一个简单但强大的热力学方法来深入了解液滴可控运动的物理本质。在自由能和自由能垒热力学计算的基础上，系统地研究了柱状微织构表面几何形状的影响。结果发现，同时减少柱的宽度和间距，需要降低前进和后退的FEB，以有效地将液滴在粗糙度梯度表面上。此外，在粗糙度梯度的配合下，外部能量在自发液滴运动的驱动中起作用。此外，通过在微通道周围构建高度超前的FEB区域，可以实现所谓的“虚拟壁”，用于限制液体沿不期望的方向沿着流动，这对于微流控系统的设计是有希望的。
Superhydrophobic surfaces have shown promising applications in microfluidic systems as a result of their water-repellent and low-friction properties over the past decade. Recently, designed microstructures have been experimentally applied to construct wettability gradients and direct the droplet motion. However, thermodynamic mechanisms responsible for the droplet motion on such regular rough surfaces have not been well understood such that at present specific guidelines for the design of tunable superhydrophobic surfaces are not available. In this study, we propose a simple but robust thermodynamic methodology to gain thorough insight into the physical nature for the controllable motion of droplets. On the basis of the thermodynamic calculations of free energy (FE) and the free-energy barrier (FEB), the effects of surface geometry of a pillar microtexture are systematically investigated. It is found that decreasing the pillar width and spacing simultaneously is required to lower the advancing and receding FEBs to effectively direct droplets on the roughness gradient surface. Furthermore, the external energy plays a role in the actuation of spontaneous droplet motion with the cooperation of the roughness gradient. In addition, it is suggested that the so-called "virtual wall" used to confine the liquid flow along the undesired directions could be achieved by constructing highly advancing FEB areas around the microchannels, which is promising for the design of microfluidic systems.