Modulation of an Induced Charge Density Gradient in the Room-Temperature Ionic Liquid BMIM+BF4

• Published in: Journal of physical chemistry. C 2018-04, Vol.122 (13), p.7361-7367
• Main Authors: Ma, Ke, Jarosova, Romana, Swain, G. M, Blanchard, G. J
• Format: Article
• Language: eng ; jpn
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.8b02345

In an earlier article (Langmuir 2016, 32, 9507–9512), we reported the existence of an induced charge density gradient, ρf, in a room-temperature ionic liquid (RTIL, BMIM+BF4 –) normal to a charged planar silica surface. In this work, we demonstrate experimental control over the sign and magnitude of the gradient. The spatial extent of ρf can exceed 100 μm from the charged surface. We characterized ρf through the rotational diffusion time constant gradient of a cationic chromophore in the room-temperature ionic liquid (RTIL). The sign and magnitude of ρf in BMIM+BF4 – is linked directly to the surface charge density of the electrode, which can be controlled. We used transparent conductive electrodes (FTO and ITO coated on glass) as supports and demonstrated that control over the electrode surface charge carrier density can influence the magnitude and sign of ρf. There are limitations to this approach based on the FTO and ITO properties, and we demonstrate these limits experimentally.