Analysis of droplet evaporation on a superhydrophobic surface
Analysis of droplet evaporation on a superhydrophobic surface
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DOI：
10.1021/la0518795
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发表时间：
2005-11-22
期刊：
影响因子：
3.9
通讯作者：
Erbil, HY
中科院分区：
文献类型：
--
作者：
McHale, G;Aqil, S;Erbil, HY
对图案化聚合物表面上直径 1-2 毫米的小水滴的蒸发过程进行了跟踪和表征。表面由排列成方格图案的SU-8光致抗蚀剂圆柱（直径5-15μm）组成，使得柱之间的中心到中心间距为20-30μm。这些类型的表面为超疏水系统提供了水滴的理论初始卡西-巴克斯特接触角高达 140-167 度，这明显大于光滑疏水表面所能达到的接触角。实验表明，在这些 SU-8 纹理表面上，水滴最初以固定接触线模式蒸发，然后接触线以逐步方式在柱子之间跳跃而后退。如果水滴在没有来自针的太大压力的情况下沉积，则初始状态似乎对应于卡西-巴克斯特状态，其中水滴位于柱的顶部。在某些情况下，但不是全部情况下，液滴会突然塌陷到柱结构中。对于这些塌陷的液滴，进一步的蒸发发生在与文泽尔型状态一致的完全钉扎的接触区域中。结果表明，可以进行基于水蒸气扩散到周围大气中的简单定量分析，并获得扩散系数和浓度差（饱和度减去环境）的乘积的估计值。
The evaporation process for small, 1-2-mm-diameter droplets of water from patterned polymer surfaces is followed and characterized. The surfaces consist of circular pillars (5-15 mu m diameter) of SU-8 photoresist arranged in square lattice patterns such that the center-to-center separation between pillars is 20-30,mu m. These types of surface provide superhydrophobic systems with theoretical initial Cassie-Baxter contact angles for water droplets of up to 140-167 degrees, which are significantly larger than can be achieved by smooth hydrophobic surfaces. Experiments show that on these SU-8 textured surfaces water droplets initially evaporate in a pinned contact line mode, before the contact line recedes in a stepwise fashion jumping from pillar to pillar. Provided the droplets of water are deposited without too much pressure from the needle, the initial state appears to correspond to a Cassie-Baxter one with the droplet sitting upon the tops of the pillars. In some cases, but not all, a collapse of the droplet into the pillar structure occurs abruptly. For these collapsed droplets, further evaporation occurs with a completely pinned contact area consistent with a Wenzel-type state. It is shown that a simple quantitative analysis based on the diffusion of water vapor into the surrounding atmosphere can be performed, and estimates of the product of the diffusion coefficient and the concentration difference (saturation minus ambient) are obtained.