Water contact angles on charged surfaces in aerosols

Interactions between water and solid substrates are of fundamental importance to various processes in nature and industry. Electric control is widely used to modify interfacial water, where the influence of surface charges is inevitable. Here we obtain positively and negatively charged surfaces using LiTaO₃ crystals and observe that a large net surface charge up to 0.1 C/m² can nominally change the contact angles of pure water droplets comparing to the same uncharged surface. However, even a small amount of surface charge can efficiently increase the water contact angle in the presence of aerosols. Our results indicate that such surface charges can hardly affect the structure of interfacial water molecular layers and the morphology of the macroscopic droplet, while adsorption of a small amount of organic contaminants from aerosols with the help of Coulomb attraction can notably decrease the wettability of solid surface. Our results not only provide a fundamental understanding of the interactions between charged surfaces and water, but also help to develop new techniques on electric control of wettability and microfluidics in real aerosol environments.     

光解水的原子尺度机理和量子动力学

利用阳光直接将水分解为不含碳的氢气燃料和氧气是面向全球能源危机环保且低成本的解决方案.得益于电子结构理论和量子模拟方法的进步,人们已经能够直接研究在纳米颗粒上等离激元诱导光解水过程在原子尺度上的反应机理和超快动力学.本文简述近年来的相关工作进展.吸附在氧化物薄膜上的金纳米颗粒很有希望成为水分解的高效新型光催化剂.在光激发条件下,水分解反应速率和光强、热电子转移之间有强相关性.水分解速率不仅取决于光吸收强度,还受到等离激元量子振动模式的调控.这对于太阳能光解水器件中纳米颗粒的设计有借鉴意义.我们发现液态水在金团簇等离激元催化下100 fs内就能产生氢气.超快量子动力学模拟表明,该过程中场增强起主导作用,从金属到水反键态的超快电荷转移也扮演着重要角色.综合这些原子尺度上的量子动力学研究,我们提出受激水分子中氢原子高速碰撞(速度远远超出其热速度)合成氢分子的"链式反应"机理.