Surface Ordering of Amphiphilic Ionic Liquids

Bowers, James; Vergara-Gutierrez, Marcos C.; Webster, John R. P.

doi:10.1021/la035495v

Cited by 186 publications

(199 citation statements)

References 28 publications

(35 reference statements)

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“…IL surface properties have been investigated by numerous surface-sensitive spectroscopic techniques and scattering methods. Initially, these studies were mainly restricted to methods that can be applied under ambient conditions, such as sum-frequency generation (SFG) [100,[109][110][111][112][113][114][115][116], X-ray reflectivity and neutron reflectometry [112,[117][118][119][120][121], grazing incidence X-ray diffraction [122], atomic force microscopy (AFM) [104,[123][124][125][126][127][128][129][130][131][132][133][134] and surface force balance (SFB) [135][136][137]. In 2005, it was realized that the surface properties of ILs can also be investigated using the well-developed techniques of ''classical'' surface science.…”

Section: Molecular Insights Into Il/gas and Il/support Interfacesmentioning

confidence: 99%

Ionic Liquids in Catalysis

2014

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Ionic liquids (ILs), salts with melting points below 100°C, represent a fascinating class of liquid materials typically characterized by an extremely low vapor pressure. Besides their application as new solvents or as electrolytes for electrochemical purposes, there are two important concepts of using ILs in catalysis: Liquid-liquid biphasic catalysis and IL thin film catalysis. Liquid-liquid biphasic catalysis enables either a very efficient manner to apply catalytic ILs, e.g. in Friedel-Crafts reactions, or to apply ionic transition metal catalyst solutions. In both cases, phase separation after reaction allows an easy separation of reaction products and catalyst re-use. One problem of liquidliquid biphasic catalysis is mass transfer limitation. If the chemical reaction is much faster than the liquid-liquid mass transfer the latter limits the overall reaction rate. This problem is overcome in IL thin film catalysis where diffusion pathways and thus the characteristic time of diffusion are short. Here, Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL) are the two most important concepts. In both, a high surface area solid substrate is covered with a thin IL film, which contains either a homogeneously dissolved transition metal complex for SILP, or which modifies catalytically active surface sites at the support for SCILL. In each concept, interface phenomena play a very important role: These may concern the interface of an IL phase with an organic phase in the case of liquidliquid biphasic catalysis. For IL thin film catalysis, the interfaces of the IL with the gas phase and with catalytic nanoparticles and/or support materials are of critical importance. It has recently been demonstrated that these interfaces and also the bulk of ILs can be investigated in great detail using surface science studies, which greatly contributed to the fundamental understanding of the catalytic properties of ILs and supported IL materials. Exemplary results concerning the IL/vacuum or IL/gas interface, the solubility and surface enrichment of dissolved metal complexes, the IL/support interface and the in situ monitoring of chemical reactions in ILs are presented.

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Section: Molecular Insights Into Il/gas and Il/support Interfacesmentioning

confidence: 99%

Ionic Liquids in Catalysis

2014

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“…Although other techniques such as infrared spectroscopy, X-ray, and neutron diffraction studies have been used to study these ions in the liquid or solid state or at surfaces [6,52,[109][110][111][112][113][114][115][116][117][118][119][120], a real gain in our understanding came with the combination of crystal structure solution, Raman spectroscopy and ab-initio DFT calculations [108,121]. We concentrate the story on the instructive example of the l-butyl-3-methylimidazolium cation, [C 4 mim] þ (see Fig.…”

Section: Brief Introduction To Ab-initio Model Calculationsmentioning

confidence: 99%

Raman Spectroscopy and Ab-Initio Model Calculations on Ionic Liquids

2007

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Summary.A review of the recent developments in the study and understanding of room temperature ionic liquids are given. An intimate picture of how and why these liquids are not crystals at ambient conditions is attempted, based on evidence from crystallographical results combined with vibrational spectroscopy and ab-initio molecular orbital calculations. A discussion is given, based mainly on some recent FT-Raman spectroscopic results on the model ionic liquid system of 1-butyl-3-methylimidazolium ([C 4 mim][X]) salts. The rotational isomerism of the [C 4 mim] þ cation is described: the presence of anti and gauche conformers that has been elucidated in remarkable papers by Hamaguchi et al. Such presence of a conformational equilibrium seems to be a general feature of the room temperature liquids. Then the ''localized structure features'' that apparently exist in ionic liquids are described. It is hoped that the structural resolving power of Raman spectroscopy will be appreciated by the reader. It is of remarkable use on crystals of known different conformations and on the corresponding liquids, especially in combination with modern quantum mechanics calculations. It is hoped that these interdisciplinary methods will be applied to many more systems in the future. A few examples will be discussed.

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“…In this case, it can be inferred that the relatively low COFs under the lubrication of Ions 2 and 3 can be partly ascribed to the formation of lubricating tribo-layers. It was also argued that surface ordering of the IL lubricant molecules was present, and longer alkyl chains on the imidazolium ring could produce better lubrication performances [36][37][38][39][40].…”

Section: Effects Of Different Il Lubricants On the Tribological Behaviormentioning

confidence: 99%

Tribological Characterization of Several Silicon-Based Materials Under Ionic-Liquids Lubrication

Xie

Wang

et al. 2009

Tribol Lett

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The tribological behaviors of three siliconbased materials (low temperature silicon oxide (LTO), polysilicon (Poly Si) and silicon nitride (Si 3 N 4 ) films) under ion liquids (ILs) lubrication have been investigated by varying the applied load and the sliding velocity. An atomic force microscope and a nanoindentor were used to characterize the deposited films, and the worn surfaces after frictional tests were analyzed by an optical microscope, a scanning electron microscope (SEM) with an energy dispersive spectrometer (EDS) and an X-ray photoelectron spectrometer (XPS). The results show the best lubricating properties of the IL lubricants are obtained at the intermediate load of 150 g for the three tribo-pairs. For the Si 3 N 4 /Si 3 N 4 tribo-pair, the coefficients of friction (COFs) and the wear rates under ILs lubrication are larger than those under dry friction. The COF values decrease with sliding velocity, and the COFs of the Si 3 N 4 /Si 3 N 4 tribo-pair are greater than the ones of the other two tribopairs (LTO/Si 3 N 4 and Poly Si/Si 3 N 4 ) at low velocities. The COF of 1-ethyl-3-methylimidazolium tetrafluoroborate is nearly 3 times larger than the other two IL lubricants (1-butyl-2,3-dimethylimidazolium tetrafluoroborate and N-butylpyridinium tetrafluoroborate) for the Si 3 N 4 /Si 3 N 4 tribo-pair. The differences in COFs between the latter two lubricants for the three tribo-pairs are negligible. Different mechanisms of these results have been analyzed in the paper.

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Surface Ordering of Amphiphilic Ionic Liquids

Cited by 186 publications

References 28 publications

Ionic Liquids in Catalysis

Ionic Liquids in Catalysis

Raman Spectroscopy and Ab-Initio Model Calculations on Ionic Liquids

Tribological Characterization of Several Silicon-Based Materials Under Ionic-Liquids Lubrication

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