Effect of Solid Substrates on the Molecular Structure of Ionic Liquid Nanofilms

• Published in: Langmuir 2021-12, Vol.37 (50), p.14753-14759
• Main Authors: Wang, Bingchen, Li, Lei
• Format: Article
• Language: English
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/acs.langmuir.1c02722

Fundamental understandings of the interfacial molecular structure of solid-confined ionic liquids (ILs) have significant impacts on the development of many cutting-edge applications. Among the extensive studies on the molecular structure at the IL/solid interface, direct observation of a double-layering quantized growth of [Cnmim]­[FAP] on mica was recently reported. In the current work, the atomic force microscopy (AFM) results directly show that the growths of [Bmim]­[FAP] nanofilms on silica and amorphous carbon are different from the double-layering growth on mica. The growth of [Bmim]­[FAP] nanofilms on silica is dominated by the aggregation of the IL molecules, which can be attributed to the inadequate negative charging of the silica surface resulting in a weak electrostatic interaction between silica and the IL cation. [Bmim]­[FAP] on amorphous carbon shows a fairly smooth film for the thinner nanofilms, which can be attributed to the π–π+ parallel stacking between the cation imidazolium ring and the randomly distributed sp2 carbon on the amorphous carbon surface. Our findings highlight the effect of different IL/solid interactions, among the several competing interactions at the interface, on the resulting molecular arrangements of various IL.