Functionalized imidazolium wear‐resistant ionic liquid ultrathin films for MEMS/NEMS applications

As a kind of new material, ionic liquids (ILs) are considered a new type of lubricant for micro/nanoelectromechanical system (M/NEMS) due to their excellent thermal and electrical conductivity. However, so far, only a few reports have investigated the friction and wear of thin films of these materials at the micro scale. Evaluating the nanoscale tribological performance of ILs when applied as films of a few nanometers thickness on a substrate is a critical step for their application in M/NEMS devices. To achieve this purpose, IL thin films with four kinds of anions were synthesized and prepared on single‐crystal silicon wafers by the dip‐coating method. Film thickness was determined by the ellipsometric method. Their surface morphologies were observed by means of atomic force microscopy (AFM). The nano and micro tribological properties of the IL films were investigated by a friction force microscope (FFM)with a spherical probe and a UMT‐2MT tribotester, respectively. The corresponding morphologies of the wear tracks of the IL films were examined using a three‐dimensional non‐contact interferometric microscope. The impact of temperature on the adhesion behavior was studied, as well as the effect of sliding frequency and load on the friction coefficient, load bearing capacity and anti‐wear durability. It was found that friction, adhesion and durability of IL films were strongly dependent on their anionic molecular structures, wettability and ambient environment. Copyright © 2010 John Wiley & Sons, Ltd.     

Micro/macrotribological properties of several nano‐scale ionic liquid films on modified silicon wafers

Three kinds of alkylimidazolium base room temperature ionic liquids (RTILs) were synthesized and their nano‐scale lubricant films were prepared on modified silicon wafers by dip‐coating method. The thicknesses of these films were measured and their relationship between thickness and solution concentration was obtained. Their surface morphologies were observed and contact angles of water on these films were determined. The adhesions and friction coefficients of these films were detected by contact mode AFM. As comparison, their macrotribological properties were evaluated on a UMT‐2MT tribo‐tester. It was found that, in microscale, 1‐hexyl‐3‐methyl‐imidazolium hexafluorophosphate performed the best tribological properties, while in macroscale, its tribological properties were similar with that of 1‐hexyl‐3‐methyl‐imidazolium tetrafluoroborate and better than that of 1‐hexyl‐3‐methyl‐imidazolium adipate. Copyright © 2009 John Wiley & Sons, Ltd.     

The tribological performance of fullerene‐like hydrogenated carbon films under ionic liquid lubrication

Fullerene‐like hydrogenated carbon films were deposited on Si substrate by plasma‐enhanced chemical vapor deposition. The microstructures of films were characterized by high‐resolution transmission electron microscopy and Raman spectrum. The tribological performance of films was tested by reciprocating ball‐on‐disc tester under 1‐ethyl‐3‐methylimidazolium tetrafluoroborate ionic liquid. The surface morphology and chemical composition of wear tracks and wear rates were investigated by optical microscope, X‐ray photoelectron spectroscopy, and 3D surface profiler. The results indicated that the film with a typical fullerene‐like structure embedded into the amorphous sp² and sp³ carbon networks could be prepared successfully, and the film shows a higher hardness (26.7 GPa) and elastic recovery (89.9%) compared with the amorphous carbon film. Furthermore, the film shows a lower friction coefficient at low contact load and friction frequency, and excellent wear‐resistance performance at high load and frequency under ionic liquid lubrication. Meanwhile, the wear life of fullerene‐like hydrogenated carbon films could be improved significantly using ionic liquid as a lubrication material. Copyright © 2015 John Wiley & Sons, Ltd.     

Micro/nanotribological behaviors of ionic liquid nanofilms with different functional cations

Four kinds of molecularly thin films of room temperature ionic liquids (RTILs) with different functional cations were prepared on silicon substrates by dip‐coating method. Thermal stability of the RTILs was evaluated using Mettler thermal gravity analysis (TGA) in a nitrogen atmosphere. Chemical compositions of the RTIL nanofilms were examined by means of multifunctional XPS. Nanoscaled adhesion and friction forces between the films and AFM tip were measured by FFM whereas the morphologies of the films were also investigated. Microscaled friction and wear behaviors between the films and Si₃N₄ ball were further measured by the microtribometer. The micro/nanotribological behaviors of different RTIL films were comparatively investigated and discussed in terms of functional cations of the RTILs molecules. Results in this paper revealed that the functional cations of the RTIL films significantly affected their tribological behaviors both in micro‐ and nanoscales. The corresponding micro/nanotribological mechanism of the tested ultrathin RTIL films under the test conditions was consequently proposed based on the experimental results. Copyright © 2010 John Wiley & Sons, Ltd.     

Preparation and tribological properties of self‐assembled poly(amide amine)‐Cu nanofilm on silicon

Self‐assembled poly(amide amine)‐copper (PAMAM/Cu) film on silicon was prepared and investigated by means of contact angle measurement, XPS and atomic force microscopy (AFM). The tribological properties were evaluated using a reciprocal ball‐on‐disc test rig and a lateral force microscope. Results of XPS show the existence of Cu(0) and PAMAM molecule on the surface of the film. Compared with the self‐assembled monolayer of the poly(amide amine) generation 4.0 dendrimer, the friction force of PAMAM/Cu film is lower and the friction coefficient is smaller which can be attributed to the existence of Cu nanoparticles. The PAMAM/Cu film shows a good lubrication effect. The stability of friction and wear resistance of film is improved. Copyright © 2011 John Wiley & Sons, Ltd.     

Determination of triazine herbicides in juice samples by microwave‐assisted ionic liquid/ionic liquid dispersive liquid–liquid microextraction coupled with high‐performance liquid chromatography

A novel microextraction method, termed microwave‐assisted ionic liquid/ionic liquid dispersive liquid–liquid microextraction, has been developed for the rapid enrichment and analysis of triazine herbicides in fruit juice samples by high‐performance liquid chromatography. Instead of using hazardous organic solvents, two kinds of ionic liquids, a hydrophobic ionic liquid (1‐hexyl‐3‐methylimidazolium hexafluorophosphate) and a hydrophilic ionic liquid (1‐butyl‐3‐methylimidazolium tetrafluoroborate), were used as the extraction solvent and dispersion agent, respectively, in this method. The extraction procedure was induced by the formation of cloudy solution, which was composed of fine drops of 1‐hexyl‐3‐methylimidazolium hexafluorophosphate dispersed entirely into sample solution with the help of 1‐butyl‐3‐methylimidazolium tetrafluoroborate. In addition, an ion‐pairing agent (NH₄PF₆) was introduced to improve recoveries of the ionic liquid phase. Several experimental parameters that might affect the extraction efficiency were investigated. Under the optimum experimental conditions, the linearity for determining the analytes was in the range of 5.00–250.00 μg/L, with the correlation coefficients of 0.9982–0.9997. The practical application of this effective and green method is demonstrated by the successful analysis of triazine herbicides in four juice samples, with satisfactory recoveries (76.7–105.7%) and relative standard deviations (lower than 6.6%). In general, this method is fast, effective, and robust to determine triazine herbicides in juice samples.     

Adhesion and friction studies of Au nanoparticle‐textured surfaces with colloidal tips

Surface roughness plays an important role in affecting the adhesive force and friction force in microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS). One effective approach of reducing adhesion and friction of contacting interfaces is to create textured surface, which is especially beneficial for MEMS'/NEMS' production yield and product reliability. In this article, we present a convenient method to fabricate the nano‐textured surfaces by self‐assembling Au nanoparticles (NPs) on the silicon (100) surfaces. The nanoparticle‐textured surfaces (NPTS) with different packing density and texture height were prepared by controlling the assembling time and the size of Au NPs. The morphologies and chemical states of NPTS were characterized by atomic force microscope (AFM), field emission scanning electron microscope, and XPS. The adhesion and friction on the NPTS were studied by AFM with colloidal tip. The results show that the nano‐textured surfaces have effectively reduced adhesive force and friction force compared with the 3‐aminopropyl trimethoxysilane self‐assembled monolayer surfaces. The lowered adhesion and friction were attributed to the reduced real area of contact between NPTS and colloidal tip. The adhesion and friction of the NPTS are varying with the texture packing density and dependent on both the texture height and asperities spacing, which are related to the size and coverage ratio of NPs on surfaces. Copyright © 2011 John Wiley & Sons, Ltd.     

Use of ionic liquid for the enzyme‐catalyzed polymerization of phenols

Ionic liquid and buffer mixture media are first reported in the peroxidase‐catalyzed polymerization of phenol. Yield of 100% with molecular weights of 7000 KDa, as assessed by size‐exclusion chromatography (SEC), were attained using 1‐butyl‐3‐methylimidazolium tetrafluoroborate–buffer mixtures with added hydrogen peroxide. The simplicity of the process and the low vapor pressure of the solvent media allow an eco‐friendly alternative to the general synthesis of polyphenolic‐type biopolymers. Evidence for the consequent polyphenol (PPO) was obtained from solid‐state ¹³C cross‐polarization magic angle spinning (CP‐MAS) NMR spectroscopy and FT‐IR. Copyright © 2009 John Wiley & Sons, Ltd.     

Ultrasound‐assisted,hybrid ionic liquid,dispersive liquid–liquid microextraction for the determination of insecticides in fruit juices based on partition coefficients

An ultrasound‐assisted, hybrid ionic liquid, dispersive liquid–liquid microextraction method coupled to high‐performance liquid chromatography with a variable‐wavelength detector was developed to detect ten insecticides, including diflubenzuron, triflumuron, hexaflumuron, flufenoxuron, lufenuron, diafenthiuron, transfluthrin, fenpropathrin, γ‐cyhalothrin and deltamethrin, in fruit juices. In this method, an appropriate extraction solvent was chosen based on the partition coefficient of the target compounds. A mixture of 1‐octyl‐2,3‐dimethylimidazolium bis(trifluoromethylsulfonyl)imide and 1‐hexyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide was used as the extractant. The extraction efficiency was screened using Plackett–Burman design and optimized using central composite design. Under the optimal conditions, good linearity was obtained for all the analytes in the pure water model and the fruit juice samples. In pure water, the recoveries of the ten insecticides ranged from 85.7 to 108.9%, with relative standard deviations for one day ranging from 1.24 to 2.64%. The limits of detection were in the range of 0.19–0.69 μg/L, and the enrichment factors were in the range of 123–160. The logarithm of the n‐octanol/water partition coefficient in this experiment is a useful reference to select a suitable extraction solvent, and the proposed technique was applied for the analysis of ten insecticides in fruit juice with satisfactory results.     

Effects of UV irradiation on tribological properties of nano‐TiO2 thin films

One‐layer and two‐layer nano‐TiO₂ thin films were prepared on the surface of common glass by sol–gel processing. Water contact angle, surface morphology, tribological properties of the films before and after ultraviolet (UV) irradiation were investigated using DSA100 drop shape analyzer, scanning probe microscopy (SPM), SEM and universal micro‐materials tester (second generation) (UMT‐2MT) friction and wear tester, respectively. The stored films markedly resumed their hydrophilicity after UV irradiation. But UV irradiation worsened tribological properties of the films. After the film was irradiated by UV, the friction coefficient between the film and GCr15 steel ball increased about 10–50% and its wear life shortened about 20–90%. Abrasive wear, brittle break and adherence wear are the failure mechanisms of nano‐TiO₂ thin films. It was believed that UV irradiation increased surface energy of the film and then aggravated adherence wear of the film at initial stage of friction process leading to severe brittle fracture and abrasive wear. Copyright © 2009 John Wiley & Sons, Ltd.     

A new ionic liquid surface‐imprinted polymer for selective solid‐phase‐extraction and determination of sulfonamides in environmental samples

Toward improving the selective adsorption performance of molecularly imprinted polymers in strong polar solvents, in this work, a new ionic liquid functional monomer, 1‐butyl‐3‐vinylimidazolium bromide, was used to synthesize sulfamethoxazole imprinted polymer in methanol. The resulting molecularly imprinted polymer was characterized by Fourier transform infrared spectra and scanning electron microscopy, and the rebinding mechanism of the molecularly imprinted polymer for sulfonamides was studied. A static equilibrium experiment revealed that the as‐obtained molecularly imprinted polymer had higher molecular recognition for sulfonamides (e.g., sulfamethoxazole, sulfamonomethoxine, and sulfadiazine) in methanol; however, its adsorption of interferent (e.g., diphenylamine, metronidazole, 2,4‐dichlorophenol, and m‐dihydroxybenzene) was quite low. ¹H NMR spectroscopy indicated that the excellent recognition performance of the imprinted polymer was based primarily on hydrogen bond, electrostatic and π‐π interactions. Furthermore, the molecularly imprinted polymer can be employed as a solid phase extraction sorbent to effectively extract sulfamethoxazole from a mixed solution. Combined with high‐performance liquid chromatography analysis, a valid molecularly imprinted polymer‐solid phase extraction protocol was established for extraction and detection of trace sulfamethoxazole in spiked soil and sediment samples, and with a recovery that ranged from 93–107%, and a relative standard deviation of lower than 9.7%.     

Bis(trifluoromethylsulfonyl)imide‐based frozen ionic liquid for the hollow‐fiber solid‐phase microextraction of dichlorodiphenyltrichloroethane and its main metabolites

1‐Hexadecyl‐3‐methylimidazolium bis(trifluoromethylsulfonyl)imide is a solid‐phase ionic organic material under ambient temperature and is considered as a kind of “frozen” ionic liquid. Because of their solid‐state and ultra‐hydrophobicity, “frozen” ionic liquids are able to be confined in the pores of hollow fiber, based on which a simple method was developed for the hollow‐fiber solid‐phase microextraction of dichlorodiphenyltrichloroethane and its main metabolites. Under optimized conditions, the proposed method results in good linearity (R ² > 0.9965) over the range of 0.5−50 μg/L, with low limits of detection and quantification in the range of 0.33−0.38 and 1.00−1.25 μg/L, respectively. Intra‐ and interday precisions evaluated by relative standard deviation were 3−6 and 1−6%, respectively. The spiked recoveries of dichlorodiphenyltrichloroethane and its main metabolites from real water samples were in the range of 64−113 and 79−112%, respectively, at two different concentration levels. The results suggest that “frozen” ionic liquids are promising for use as a class of novel sorbents.     

Adjusting the chromatographic properties of poly(ionic liquid)‐modified stationary phases by substitution on the imidazolium cation

Poly(ionic liquid)‐modified stationary phases can have multiple interactions with solutes. However, in most stationary phases, separation selectivity is adjusted by changing the poly(ionic liquid) anions. In this work, two poly(ionic liquid)‐modified silica stationary phases were prepared by introducing the cyano or tetrazolyl group on the pendant imidazolium cation on the polymer chains. Various analytes were selected to investigate their mechanism of retention in the stationary phases using different mobile phases. Two poly(ionic liquid)‐modified stationary phases can provide various interactions toward solutes. Compared to the cyano‐functionalized poly(ionic liquid) stationary phase, the tetrazolyl‐functionalized poly(ionic liquid) stationary phase provides additional cation‐exchange and π‐π interactions, resulting in different separation selectivity toward analytes. Finally, applicability of the developed stationary phases was demonstrated by the efficient separation of nonsteroidal anti‐inflammatory drugs.     

Covalently attached self‐assembly of ultrathin films from hydroxy‐containing porphyrin and diazoresin

Ultrathin films from 5,10,15,20‐tetrakis(4‐hydroxyphenyl) porphyrin (HPP) and diazoresin (DR) via a H bonding interaction were fabricated with the self‐assembly technique. Under UV irradiation, the H bonds between the layers will convert to covalent bonds following the decomposition of the diazonium group of DR. The stability of the film against the polar solvent and electrolyte aqueous solution increases a lot because of the formation of the covalent crosslinking structure. Thus, the photoelectric conversion property of DR/HPP film can be measured directly with a normal photoelectric chemical cell with potassium chloride as the electrolyte. The maximum of the anodic photocurrent was measured as 1.7 μ Å for an eight bilayer DR/HPP film deposited on an indium–tin oxide glass electrode. The action spectrum of the photocurrent generation indicated that the HPP contained in the film is responsible for the generation of the observed photocurrent. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3103–3108, 2003     

Mechanical and electrical properties of the phosphor‐doped nano‐silicon film under an external electric field

The mechanical and electrical properties of the phosphor‐doped nano‐silicon film (nc‐Si:H) prepared by the plasma‐enhanced chemical vapor deposition (PECVD) method under electric field have been studied by Tribolab system, which is equipped with nano‐electrical contact resistance (ECR) tool. During indentation, different voltages and loads were applied. The topography of the sample surface was studied by atomic force microscopy (AFM). The experimental results show that the roughness of the film is 5.69 nm; the electric current was measured through the sample/indenter tip with different loads at a fixed voltage, and it increased nonlinearly during the indentation. The maximum current value depth was shallower than the maximum depth of each indent due to the plasticity of the film. When the loading speed is increased to 250 µN/s, the microcrack occurred on the film; the hardness (H) and elastic modulus (E) changed with the voltage applied both in open circuit and in short circuit case, which resulted in different values of H/E rate from 0.082 to 0.096. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal‐ and collision‐induced dissociation studies of functionalized imidazolium‐based ionic liquid cations

Ionic liquids are now used in applications ranging from chemical synthesis to spacecraft propulsion. With this comes the need to characterize new syntheses, identify environmental contamination, and determine eventual fate in terrestrial and space environments. This work investigates the effects of source conditions, particularly capillary temperature, on the observed mass spectrum and determines the collision‐induced dissociation (CID) patterns of imidazolium‐based ionic liquid cations as a function of their substituent types. Experiments were carried out on a Thermo LTQ‐XL ion‐trap mass spectrometer and a Bruker microTOF‐Q II mass spectrometer. Dissociation of the imidazolium cations occurred predominantly via substituent losses, except in benzyl‐substituted systems, for which the neutral loss of the imidazole was exclusively observed. Several of these dissociation pathways were studied in greater depth using complementary quantum chemical calculations. The nature of the neutral losses from the substituents was found to be highly dependent upon the nature of the substituent, as would be expected, establishing bases for characterization.     

Microspheres from stereocomplexes of polylactides containing ionic liquid end‐groups

Low‐molecular‐weight polymers of L ‐ and D ‐lactide containing different end‐groups (hydroxy, butoxy, trifluoromethoxy, heptafluorobutoxy, oxyethylimidazole groups, and groups derived from the imidazolium ionic liquid) are synthesized. It is shown that the nature of end‐groups affects the stereocomplexation of corresponding pairs of polymers. Stereocomplex of poly(L ‐lactide) and poly(D ‐lactide) containing imidazolium ionic liquid end‐groups (PLA‐IL) precipitates from 1,4‐dioxane solution in the form of monodisperse, perfectly spherical microspheres. Such behavior of PLA‐IL, not observed for polymers containing other end‐groups, can be attributed to the presence of strongly interacting ionic liquid end‐groups. This conclusion is supported by the results of ¹H NMR and dynamic light scattering experiments as well as by direct observation of precipitated particles by scanning electron microscopy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Swelling behavior of gelatin‐ionic liquid functional polymers

In this work, hydrogels obtained by mixing gelatin with ionic liquids (ILs) are prepared. Two different ILs, [emim][EtSO₄] and [bmim][N(CN)₂], are used to prepare hydrogels with different amounts of starting water and phosphate buffer content, which are used after a maturation period. The percentage of swelling in water and phosphate buffer, swelling and diffusion parameters are investigated in thin‐film polymers (1 × 1 cm²; 1‐mm thick) with different maturation times and at temperatures ranging from 4 to 37 °C. [emim][EtSO₄] polymers show a moderate (100% weight increase) but quick swelling that reaches 80% of the equilibrium within 30 min. They are liquefied and dissolved at temperatures above 25 °C. [bmim][N(CN)₂] polymers with short maturation times exhibit a similar behavior to the former, but more mature hydrogels register a very small swelling, abnormal kinetics and are more resistant to higher temperatures. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys., 2013     

Dicationic imidazolium ionic liquid modified silica as a novel reversed‐phase/anion‐exchange mixed‐mode stationary phase for high‐performance liquid chromatography

A dicationic imidazolium ionic liquid modified silica stationary phase was prepared and evaluated by reversed‐phase/anion‐exchange mixed‐mode chromatography. Model compounds (polycyclic aromatic hydrocarbons and anilines) were separated well on the column by reversed‐phase chromatography; inorganic anions (bromate, bromide, nitrate, iodide, and thiocyanate), and organic anions (p‐aminobenzoic acid, p‐anilinesulfonic acid, sodium benzoate, pathalic acid, and salicylic acid) were also separated individually by anion‐exchange chromatography. Based on the multiple sites of the stationary phase, the column could separate 14 solutes containing the above series of analytes in one run. The dicationic imidazolium ionic liquid modified silica can interact with hydrophobic analytes by the hydrophobic C₆ chain; it can enhance selectivity to aromatic compounds by imidazolium groups; and it also provided anion‐exchange and electrostatic interactions with ionic solutes. Compared with a monocationic ionic liquid functionalized stationary phase, the new stationary phase represented enhanced selectivity owing to more interaction sites.     

Reversed‐phase ion‐pair solid‐phase extraction and ion chromatography analysis of pyrrolidinium ionic liquid cations in environmental water samples

A method of reversed‐phase ion‐pair solid‐phase extraction combined with ion chromatography for determination of pyrrolidinium ionic liquid cations (N‐methyl‐N‐ethyl pyrrolidinium, N‐methyl‐N‐propyl pyrrolidinium, and N‐methyl‐N‐butyl pyrrolidinium) in water samples was developed in this study. First, ion‐pair reagent sodium heptanesulfonate was added to the water samples after static, centrifugation and filteration. Then, pyrrolidinium cations in the samples were enriched and purified by a reversed‐phase solid‐phase extraction column, and eluted from the column with methanol aqueous solution as eluent. Finally, the eluate collected was analyzed by ion chromatography. The separation and direct conductivity detection of these pyrrolidinium cations by ion‐exchange column using 1.0 mM methanesulfonic acid (in water)/acetonitrile (97:3, v:v) as mobile phase was achieved within 10 min. By using this method, pyrrolidinium cations in Songhua River and Hulan River were successfully extracted with the recoveries ranging from 74.2 to 97.1% and the enrichment factor assessed as 60. Pyrrolidinium cations with the concentration of 0.001?0.03 mg/L can be enriched and detected in the water samples. The developed method for the determination of pyrrolidinium ionic liquid cations in water samples is simple and reliable, which provides a reference for the study of the potential impact of ionic liquids on the environment.