Self-Assembled Multilayer Structures of Imidazolium Based Ionic Liquids at Mica Interfaces Are Induced By Confinement and the Presence of Water

• Published in: Meeting abstracts (Electrochemical Society) Vol. MA2016-02; no. 47; p. 3530
• Main Authors: Cheng, Hsiu-Wei, Dienemann, Jan-Niklas, Stock, Philipp, Merola, Claudia, Chen, Ying-Ju, Valtiner, Markus
• Format: Journal Article
• Language: English
• Published: 01.09.2016
• ISSN: 2151-2043; 2151-2035
• DOI: 10.1149/MA2016-02/47/3530

Tuning chemical structure and molecular layering of ionic liquids (IL) at solid interfaces offers leverage to design performance of ILs in emerging technologies including super-capacitors, heterogeneous catalysis or lubrication. Recent experimental interpretations suggest that ILs containing cations with long hydrophobic tails form well-ordered bilayers at interfaces. Here we demonstrate that interfacial bilayer formation is insignificant and not an intrinsic quality of hydrophobic ILs. In contrast, bilayer formation is triggered by boundary conditions including confinement and humidity present in the IL. Therefore, we performed force versus distance profiles using atomic force microscopy and the surface forces apparatus. Our results support models of disperse low-density bilayer formation in confined situations, and at high surface charging in the presence of water. Conversely, interfacial structuring of long-chain ILs in dry environments and at low surface charging is disordered and bulk structuring also dominates interface structures in confinement. Our results demonstrate that boundary conditions such as charging, confinement and the presence of impurities drive structure formation of ILs at interfaces, while at low surface charge solvophobic interactions have a much weaker influence on interface structuring than generally believed. These results have important implications for understanding solid/IL interfaces and clarify previous interpretations.