Zhang Wangyang, Zhang Dongdong, Yan Weishan, Luo Wenyao, Zhao Chaopeng, Liu Duo
State Key Laboratory of Crystal Materials , Shandong University , 27 South Shanda Road , Jinan , Shandong 250100 , P. R. China.
Langmuir. 2019 Nov 19;35(46):14791-14796. doi: 10.1021/acs.langmuir.9b02629. Epub 2019 Nov 7.
The design and fabrication of surfaces that support rapid wetting transition remain technologically challenging. Here, we examine the effects of optical illumination on the wetting behaviors of zinc oxide (ZnO) single crystals. We find that ultraviolet irradiation above the band gap energy promotes a rapid wetting transition, characterized by sliding of the water droplet, within a few seconds. Notably, the transition for Zn-polar (0001) ZnO surfaces is even faster than that for O-polar (0001̅) ZnO surfaces. We confirmed that process is dependent on power, surface polarity, and solution pH and reversible through illumination by near-infrared light, which restores the water contact angle back to its initial value. Surface chemical analysis revealed that the instantaneous photocatalytic formation of surface-terminated hydroxyl (-OH) groups is responsible for the observed rapid wetting transition. Density functional theory calculations with the inclusion of onsite Coulomb interactions revealed that both the Zn-polar and O-polar surfaces can be easily covered with -OH groups through the adsorption of -OH groups or hydrogen atoms, respectively. This study develops a route to fabricate optically active and controllable microfluidic devices that support rapid wetting transitions for water droplet manipulation.
设计和制造能够支持快速润湿转变的表面在技术上仍然具有挑战性。在此，我们研究了光照对氧化锌（ZnO）单晶润湿行为的影响。我们发现，高于带隙能量的紫外线照射会促进快速润湿转变，其特征是水滴在几秒钟内滑动。值得注意的是，锌极性（0001）ZnO表面的转变甚至比氧极性（0001̅）ZnO表面的转变更快。我们证实该过程取决于功率、表面极性和溶液pH值，并且通过近红外光照射是可逆的，这会使水接触角恢复到其初始值。表面化学分析表明，表面终止的羟基（-OH）基团的瞬时光催化形成是观察到的快速润湿转变的原因。包含在位库仑相互作用的密度泛函理论计算表明，锌极性和氧极性表面分别可以通过吸附-OH基团或氢原子而容易地被-OH基团覆盖。这项研究开发了一种制造光学活性和可控微流体装置的途径，该装置支持用于水滴操纵的快速润湿转变。
