Surface charge dependent structure of ionic liquid/alkali halide interfaces investigated by atomic force microscopy

Abstract

Abstract Ionic liquid (IL)/solid interfaces are relevant to a broad range of physicochemical phenomena and technological processes such as catalysis, corrosion, electrochemistry, and lubrication. Hence, understanding the effect of substrate surface nature on the interfacial properties has a significant impact on improving technological processes in which interfacial properties are dominant. In this work, we investigated interfacial structures between 1-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF6) IL and KBr crystal surfaces by frequency modulation atomic force microscopy utilizing a quartz tuning fork sensor. KBr(100) and (111) surfaces were used as the substrates, where the (100) surface is electrically neutral, and the (111) surface is highly charged. We investigated the influence of surface charge on their surface structures and interfacial solvation structures by atomic-scale topographic imaging and frequency shift versus distance curve measurement. The behavior of IL at these two interfaces was found to be significantly different due to these different surface properties.