Department of Cogno-mechatronics Engineering, Pusan National University , Busan 609-735, Korea.
BK21+Nano-integrated Cogno-mechatronics Engineering, Pusan National University , Busan 609-735, Korea.
ACS Appl Mater Interfaces. 2016 Nov 2;8(43):29770-29778. doi: 10.1021/acsami.6b09541. Epub 2016 Oct 19.
The effects of the continuity of the surface pattern on wetting enhancement was investigated using micropillar and microhole arrays on hydrophilic and hydrophobic materials. Isolated micropillar arrays and continuous microhole arrays were prepared by a microscale imprinting technique using positive and negative Si molds fabricated by a conventional photolithography technique. The contact angles (CAs) and contact angle hysteresis (CAH) of the prepared surfaces were measured as a function of the surface parameter ξ, defined as the ratio of the top surface area of the microstructure to the surface area of the flat unit cell. It was found that the CAs of the micropillar array monotonically increased as the surface ratio decreased, regardless of the native wettability of the solid. However, an abnormal and consistent decrease of the CAs for the microhole array was observed when ξ < 0.5. To investigate the mechanism of this abnormality in wetting enhancement, the energy barriers for normal direction wetting, the so-called wetting transition from Cassi-Baxter (CB) wetting to Wenzel wetting, and lateral direction wetting, that is, spreading, were investigated with consideration of the trapped air in the microhole. The analysis unveiled that the hydrophobicity of the hydrophilic surfaces are attributable to the liquid-air interface pinning at the discontinuous edge of the pillar, which results in CB wetting. The abnormal decrease in the CAs of the microhole-patterned surfaces with ξ < 0.5 has been attributed to the relatively low energy barrier for spreading influenced by the continuity of the three-phase contact line. Additionally, trapped air in the microhole also plays a role in the spreading of water droplets by hindering the wetting transition from CB wetting to Wenzel wetting.
采用微尺度压印技术，通过传统光刻技术制备正、负硅模具，在亲水和疏水材料上制备了微柱和微孔阵列，研究了表面图案连续性对润湿增强的影响。孤立的微柱阵列和连续的微孔阵列。通过微尺度压印技术制备，采用常规光刻技术制备正、负硅模具。作为表面参数 ξ 的函数，测量了制备表面的接触角（CA）和接触角滞后（CAH），定义为微结构的顶表面积与平面单元表面积的比。结果表明，无论固体的固有润湿性如何，微柱阵列的 CA 都随着表面比的降低而单调增加。然而，当 ξ < 0.5 时，观察到微孔阵列 CA 的异常一致下降。为了研究润湿增强异常的机制，考虑到微孔中的被困空气，研究了法向润湿的能量势垒，即所谓的从 Cassi-Baxter (CB) 润湿向 Wenzel 润湿的润湿转变，以及侧向润湿，即扩展。分析表明，亲水表面的疏水性归因于微柱不连续边缘处的液-气界面钉扎，导致 CB 润湿。具有 ξ < 0.5 的微图案化表面的 CA 异常下降归因于受三相接触线连续性影响的扩展的相对较低的能量势垒。此外，微孔中的被困空气也通过阻碍从 Cassi-Baxter 润湿向 Wenzel 润湿的润湿转变，在液滴扩展中起作用。
