Surface behaviour of 1-alkyl-3-methylimidazolium ionic liquids at the air-water interface
Molecular dynamics simulations snapshots and electron density determined by X-ray reflectivity on layers of C20mimNTf2 ionic liquid at the air water interface undergoing a monolayer to trilayer transition with increase of surface density. [Display omitted] •1-alkyl-3-methylimidazolium ionic liquids...
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Published in | Journal of molecular liquids Vol. 370; p. 121028 |
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Main Authors | , , , , , , , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier B.V
15.01.2023
Elsevier |
Subjects | |
Online Access | Get full text |
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Summary: | Molecular dynamics simulations snapshots and electron density determined by X-ray reflectivity on layers of C20mimNTf2 ionic liquid at the air water interface undergoing a monolayer to trilayer transition with increase of surface density.
[Display omitted]
•1-alkyl-3-methylimidazolium ionic liquids with chain longer than 16 carbons and with NTF2 cation forms Langmuir monolayers.•For [C20mim][NTf2], X-ray diffraction reveal a transition from an expanded monolayer to a trilayer organized structure.•The monolayer to trilayer transition was reproduced by atomistic molecular dynamics simulations.
The ability of 1-alkyl-3-methylimidazolium ionic liquids, [Cnmim][X], to form layers at the air–water interface has been investigated systematically for the first time: five different chain lengths of the cation, n = 12, 14, 16, 18, 20 were studied, combined with three different anions, namely [N(Tf)2]−, [PF6]− and [Cl]−. The results show that only cations with chains longer than n = 16, combined with the [N(Tf)2]− anion form stable monolayers at the air/water interface, allowing measurable surface pressure vs area per molecule (π-A) isotherms immediately after spreading. The films of [C20mim][N(Tf)2] on water have been characterised using Brewster angle microscopy (BAM), Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS), specular X-ray reflectivity (XRR) and grazing incidence X-ray diffraction (GIXD). Additionally, atomistic molecular dynamics simulations were also performed to obtain a molecular level interpretation of the experimental results. The results are compatible with a transition from an expanded monolayer to a trilayer structure, followed by the 3D collapse of the film. |
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ISSN: | 0167-7322 1873-3166 |
DOI: | 10.1016/j.molliq.2022.121028 |