Variation of interfacial electric fields on molecular length scales are important for chemistry on surfaces. These variations are complicated to study and model, especially when the interface involves large ions at high concentrations such as room temperature ionic liquids. An experimentally accessible method of measuring electric fields is through the use of vibrational Stark effect. We have used self-assembled monolayers (SAM) of 4-mercaptobenzonitrile, a known Stark shift reporter, to study the electric fields at the junction of gold substrates and various ionic liquids of varying anion sizes. First, based on the sign of frequency shift, we found that in all of the ionic liquids studied, there was evidence that the cations formed the closest layer adjacent to the SAM. Second, we found a correlation between the electric field and anion size, with smaller anions producing larger electric fields. We suspect that this trend arises because the size of the anion affects the packing density of the cations near the surface. These findings are important for understanding the intimate relationship between electric fields and ionic structure at interfaces, which is relevant to many electrochemical processes.<br/>

Dependence of interfacial electric fields on anion size of ionic liquids

2019 Spring National Meeting

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