Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, 1206 W. Green Street, Urbana, Illinois 61801, USA.
Langmuir. 2012 Sep 18;28(37):13441-51. doi: 10.1021/la302669g. Epub 2012 Sep 4.
In the present study, contact angle hysteresis and sliding behavior of water droplets on parallel, periodic microgrooved brass surfaces are investigated experimentally for enhancement of water drainage and compared to that on flat baseline surfaces. The surfaces (a total of 17 microgrooved samples, with a range of groove depth of 22 to 109 μm, pillar width of 26 to 190 μm, and groove width of 103 and 127 μm) are fabricated using a mechanical micromachining process. The wetting state and shape/elongation of deposited water droplets, anisotropy of the contact angle hysteresis, and the drainage behavior of water droplets on the microgrooved surfaces are found to be strongly dependent on the topography of the groove geometry, which is analyzed in detail. The wetting state is found to be Wenzel for microgrooved surfaces with very low aspect ratio (<0.2) and narrow pillars (pillar width to groove width ratio of ≈0.2), and also for the two deepest grooved surfaces of two different sample series, all of which exhibit high contact angle hysteresis. Mechanisms of the advancing and receding motions are identified. The critical sliding angle (the angle from horizontal at incipient motion of the advancing confluence) for the microgrooved surfaces is found to be significantly smaller than for flat surfaces. The sliding angle exhibits significant groove geometry dependence and is found to increase with pillar width and decrease with groove depth. The findings of this study may be useful in a broad range of applications where water retention plays an important role.
在本研究中，通过实验研究了平行周期性微槽黄铜表面上水滴滴的接触角滞后和滑动行为，以增强排水性能，并将其与平面基底表面进行了比较。这些表面（共 17 个微槽样品，槽深范围为 22 至 109μm，支柱宽度为 26 至 190μm，槽宽为 103 和 127μm）是通过机械微加工工艺制造的。研究发现，沉积水滴的润湿状态和形状/伸长率、接触角滞后的各向异性以及微槽表面上水滴的排水行为强烈依赖于槽几何形状的形貌，对其进行了详细分析。对于非常低纵横比（<0.2）和窄支柱（支柱宽度与槽宽比约为 0.2）的微槽表面，以及两个不同样品系列中两个最深的槽表面，润湿状态被发现为 Wenzel，所有这些表面都表现出高接触角滞后。确定了前进和后退运动的机制。发现微槽表面的临界滑动角（前进汇聚初始运动时与水平方向的夹角）明显小于平面表面。滑动角表现出显著的槽几何形状依赖性，随着支柱宽度的增加而增加，随着槽深的减小而减小。本研究的发现可能在广泛的应用中有用，在这些应用中，水的保留起着重要作用。
