Guangdong Provincial Key Laboratory of Optical Information Materials and Technology and Institute of Electronic Paper Displays South China Academy of Advanced Optoelectronics, South China Normal University, Guangzhou 510006, P. R. China.
Phys Chem Chem Phys. 2019 Dec 11;21(48):26284-26291. doi: 10.1039/c9cp04436a.
The low voltage electrowetting response of a LiCl aqueous solution on a freshly cleaved surface of highly oriented pyrolytic graphite (HOPG) is presented. For applied voltages below 1 V, the energy stored in the electrical double layer (EDL) is insufficient to drive the spreading of the drop due to the pinning of the three phase contact line at the step edges. Electrochemical impedance spectroscopy shows a dramatic increase in capacitance above 1 V, which provides a sufficient electrowetting force for depinning the contact line, resulting in a subsequent decrease of the contact angle. The transition of the interfacial capacitance from the EDL to the many-fold high capacitance of the pseudocapacitor drives the electrowetting transition on the HOPG surface. The observed changes in the capacitances above 1 V are correlated with the cyclic voltammetry and atomic force microscopy results, which show that the Cl- ions intercalate into the graphite galleries upon acquiring sufficient energy to overcome the van der Waals attraction between the graphene layers through the side of the step edge of the basal planes. To the best of our knowledge, this is the first study on the voltage dependent intercalation mediated transition of interfacial capacitance driving the spreading of an aqueous electrolyte drop on the HOPG surface, which provides a fundamental understanding of the mechanism and opens up potential applications in microfluidics and charge storage technologies.
本文介绍了在高取向热解石墨（HOPG）的新鲜解理表面上，LiCl 水溶液的低电压电润湿响应。对于低于 1 V 的应用电压，由于三相接触线在台阶边缘处被钉扎，双电层（EDL）中存储的能量不足以驱动液滴的扩展。电化学阻抗谱显示，在 1 V 以上时电容急剧增加，这为解吸接触线提供了足够的电润湿力，从而导致接触角随后减小。界面电容从 EDL 向赝电容的多倍高电容的转变驱动了 HOPG 表面的电润湿转变。在 1 V 以上观察到的电容变化与循环伏安法和原子力显微镜结果相关联，这表明 Cl-离子在获得足够的能量以克服范德华吸引力后，通过基面的台阶边缘的侧面插入到石墨层间。据我们所知，这是首次研究界面电容的电压相关嵌入介导的转变如何驱动水溶液滴在 HOPG 表面的扩展，这为该机制提供了基本的理解，并为微流控和电荷存储技术开辟了潜在的应用。
