Anion Alkyl Chain Length Research Articles

Alkyl chain length affecting the structure and interactions of choline-based amino acid ionic liquids: Insights from a computational study

The influences of the alkyl chain length of amino acid anions on the structure and interactions of choline-based amino acid ([Cho][AA]) ionic liquids were investigated based on density functional theory (DFT) and molecular dynamics (MD) simulations. The most stable configuration of the individual [Cho][AA] ion pair was determined, revealing negligible variations in the binding energy between choline cation ([Cho]+) and different amino acid anions ([AA]−). To further characterize the intermolecular interactions between charged entities, the atoms in molecules theory (AIM) and independent gradient model based on Hirshfeld partition (IGMH) were employed, which highlight the presence of robust hydrogen bonds between [Cho]+ and [AA] −, underscoring their significance in shaping the structure of [Cho][AA] ion pairs. The MD studies exhibited the aggregation of anions in [Cho][AA] ILs, which was attributed to side chain interactions of anions. This aggregation effect becomes more pronounced with the elongation of anionic alkyl chain. Simultaneously, radial distribution functions (RDF) analysis revealed a higher probability of hydrogen bonds occurring between [Cho]+ and [AA]− as the alkyl chain in [AA]− lengthened. Additionally, the hydrogen bond lifetimes roughly display an increasing trend as the alkyl chain of the [AA]− increases, which may be due to the reduced diffusion coefficients of ions. Hopefully, our results would contribute fundamental knowledge regarding the impact of alkyl chain length of anions on the structure and interactions in the choline-based amino acid ionic liquids.

Effect of Anionic Alkyl Chain Length on Tribological Properties of Ionic Liquids: Molecular Dynamics Simulations

Effect of Anionic Alkyl Chain Length on Tribological Properties of Ionic Liquids: Molecular Dynamics Simulations

Sustainable approach to recover β-carotene and astaxanthin from Phaffia rhodozyma grown in a stirred-tank bioreactor under the influence of magnetic fields

This study aimed to produce carotenoids by Phaffia rhodozyma in a stirred-tank bioreactor under the influence of magnetic fields (MF) and to evaluate a sustainable approach to recover them from the yeast biomass. MF application proved to be effective in increasing 8.6 and 22.9 % of β-carotene and astaxanthin production, respectively. Regarding solid–liquid extraction (SLE), the ability of aqueous and ethanolic solutions of protic ionic liquids (PILs) was determined. β-carotene and astaxanthin recovery yields increased with the anion alkyl chain length hydrophobicity. [Pro][Oct]:EtOH (50 % v v-1) was selected as the effective solvent. Moreover, it led to improvement in carotenoid stability at different storage temperatures over time in comparison with the control. This study is one of the first to describe an effective and sustainable approach to move carotenoid production from shake flasks to a bioreactor under the influence of MF and recover carotenoids from P. rhodozyma biomass.

Combining Tailored Ionic Liquids with Ti3C2Tx MXenes for an Enhanced Load‐Carrying Capacity Under Boundary Lubrication

To improve the efficiency and lifetime of mechanical components, new lubrication systems are needed. Two complementary material classes, which have demonstrated a promising tribological performance, are ionic liquids and MXenes (2D transition metal carbides and nitrides). Herein, Ti3C2Tx MXenes are used as additives in ionic liquids (ILs) to improve their load‐carrying capacity under boundary lubrication. The specifically synthesized ILs share the same cation (trioctyl(methyl)phosphonium) but different anions (dimethyl phosphate and dibutyl phosphate for IL1 and IL2, respectively) to assess the effect of the anion's alkyl chain length. The wear reduction performance is tested with a cylinder‐on‐ring contact in a standardized Brugger tester, which is suitable to study boundary lubrication and to assess the antiwear ability of the IL/MXene lubricant blends. MXenes indicate an excellent dispersibility in both ILs over 24 h. It is found that, irrespective of the used IL, the addition of MXenes always increases the load‐carrying capacity. Particularly, significantly reduced wear and thus a high load‐carrying capacity are observed for the combination IL2/MXenes, which also outperform fully formulated commercially available lubricants such as turbine oils.

Experimental and Theoretical Studies of the Corrosion Inhibition Performance of Fatty Acid-based Ionic Liquids for Mild Steel in 1 M HCl: Effects of the Varied Alkyl Chain Length in the Anionic Group

Five fatty acid-based ionic liquids (FAILs) with various anionic alkyl chain lengths are synthesized, namely methyltrioctylammonium butyrate ([N8881][C4:0]), methyltrioctylammonium caproate ([N8881][C6:0]), methyltrioctylammonium octanoate ([N8881][C8:0]), methyltrioctylammonium laurate ([N8881][C12:0]), and methyltrioctylammonium palmitate ([N8881][C16:0]), to investigate the potential effects of anionic alkyl chains on their corrosion inhibition property for mild steel in 1 M HCl solution via X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, contact angle measurements, electrochemical measurements, and weight loss measurements. The results reflect that the FAIL inhibitor can adsorb on the surface of mild steel to form a protective film and effectively inhibit the corrosion. [N8881][C8:0] exhibits the optimal inhibition efficiency (96.94%) in comparison to [N8881][C4:0] (80.73%), [N8881][C6:0] (89.34%), [N8881][C12:0] (90.69%), and [N8881][C16:0] (74.42%). It is speculated that the varied anionic alkyl chain length may change the intensity of the protective film to affect the inhibition efficiency. The in-depth analysis by molecular dynamic simulation confirms that [N8881][C8:0] with the same anionic and cationic alkyl chain lengths shows the most ordered and compact film on the mild steel surface. The present study focuses on the effects of the anionic alkyl chain on the corrosion inhibition performance and provides novel insights into the design and development of effective and eco-friendly ionic liquids as corrosion inhibitors.

(Invited) Effects of Halide Anion Type and Alkyl Chain Length on Hydrogen Bonding in Eutectic Solvent System

Deep eutectic solvent (DES), formed by the intermolecular hydrogen bonding between its components of an H–bond acceptor (HBA) and an H–bond donor (HBD), has been extensively studied in the area of material synthesis, catalysis, electrochemistry, etc. The properties of DES including melting point, color, density, viscosity, conductivity, etc. are closely related to the H-bond network. Establishing an understanding of the H-bond structure offers an opportunity to fine-tune these properties.Hence, in this study, we systematically investigated the effects of halide anion type and alkyl chain length on the hydrogen bond network of a series of eutectic solvent systems and attempted to establish an unambiguous H-bond correlation with the conductivity. We varied the halide anion from Cl− to I− (Cl−, Br−, I−) and the alkyl chain length from methyl to butyl (n c = 1, 2, 4), and performed FTIR and conductivity measurements. Results show that the OH stretching peak exhibits a blue shift with the halide anion varies in the order of Cl−, Br−, I− when compared with the neat ethylene glycol (Figure 1a), indicating an increase in H-bond strength. A similar trend can be found with the increasing alkyl chain length as well. A stronger H-bond network inhibits the mobility of these halide anions in the eutectic system, as a result, the conductivity will decrease as shown in Figure 1b. Further probing the H-bond network with ultrafast spectroscopy is currently underway. Figure 1. (a) FTIR spectrum of neat EG and TBAX:EG(1:10) sample, X= Cl−, Br−,I−. (b) Trend between the OH stretching peak shift (vs. neat EG) and conductivity of these investigated samples.AcknowledgememtsThis work was supported as part of the Breakthrough Electrolytes for Energy Storage (BEES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DE-SC0019409 Figure 1

Ion Dynamics and Charge Transport in Imidazolium Chloroaluminate Ionic Liquids

Ion dynamics and charge transport in a homologous series of imidazolium chloroaluminate ionic liquids are investigated by broadband dielectric spectroscopy, rheology, viscometry, and differential scanning calorimetry. The interplay of anion speciation and alkyl chain length on local and mesoscale dynamics and the corresponding influence on the dc ionic conductivities, zero-shear viscosities, and static dielectric permittivities is investigated. These results are presented within a broader framework of current understanding of dynamics and transport properties of aprotic ionic liquids.

Quantification of the interactions in halide-anion-based imidazolium ionic liquids

Non-covalent interactions between constituent ions of ionic liquids (ILs) define their distinctive physicochemical properties and are critical for understanding their micro and bulk structures as well as designing new task-specific ILs. Therefore, the quantification of these interactions can improve our understanding of this unique class of materials. A set of 20 halide-anion-based imidazolium ILs (Cnmim X, X = Cl, Br, I, and BF4; n = 2, 4, 6, 8, and 10) was selected for this study. The variation of the anion (hydrogen-bond-acceptor property and size), presence of water, and the alkyl chain length of the imidazolium ring have all been considered as parameters when attempting to address mainly the following two fundamental questions: How does the strength of hydrogen bonding in these selected Coulomb systems change? How much do dispersion forces play a role in the net attractive interaction energy despite being weak? To this end, dispersion-corrected density functional theory (DFT) computations were executed to acquire the optimized structures of all the considered ILs, followed by an ensemble of NCI and QATIM analyses to explore the strength of non-covalent interactions. Further, quantum mechanical energy decomposition analysis (QM-EDA) based on symmetry-adapted-perturbation-theory (SAPT) has been employed to dissect the total interaction energy into its components. An assessment of QM-EDA demonstrates that the electrostatic interaction dominates the intermolecular attraction, although induction and dispersion components also play a substantial role. The dispersion energies are amplified when water is present, as well as when anion size and alkyl chain length increase. We quantified the non-covalent interactions between ion pairs using NCI-RDG and Bader's QTAIM analyses. Strong hydrogen bonding with a partial covalent character was observed between monoatomic anions and C2-proton of the imidazolium ring, but for the multiatomic anion (BF4−) and interaction between imidazolium ring alkyl groups and anions, a weak electrostatic hydrogen bonding was found. The hydrogen bonding strength decreases with increasing anion size; it is strongest in the C2mim Cl ion pair. NBO analysis gives a clear indication of nX→σC−H*(X=Cl,Br,I,andF) type intermolecular interaction with highest stabilization energy (En→σ*(2)). A clear correlation between E(2) and hydrogen bond lengths were observed. Overall, the current study illuminates the intricate network of covalent-like and non-covalent interactions in selected imidazolium ILs based on halide anions.

Characterization of cholinium-carboxylate-based aqueous biphasic systems

In the past years, large efforts have been placed in the development of novel separation techniques with improved resolution, simplicity, speed and easy to scale-up. Among these, ionic-liquid-based (IL-based) aqueous biphasic systems (ABS) have been broadly proposed for the separation of high-value compounds, allowing improved extraction performance and purification. More recently, significant efforts have been arranged on the synthesis and use of novel ILs with both an acceptable environmental footprint and enhanced biocompatibility. In this sense, this work aims to characterize ABS composed of cholinium carboxylate ILs ([Ch][CnO2], with n = 2 to 7), K3PO4 and water. The respective ternary phase diagrams, including binodal curves, tie-lines and tie-line lengths, were determined at (298 ± 1) K and at atmospheric pressure. The ability to form ABS (or of the IL to be salted-out) increases with the increase of the alkyl chain length of the IL anion, up to [Ch][C5O2]; nevertheless, for longer anion alkyl chain lengths ([Ch][C6O2] and [Ch][C7O2]) the ILs self-aggregation leads to a decrease of the ILs ability to form ABS. The liquid−liquid equilibrium data experimentally determined were modeled using the local composition activity coefficient model NRTL (Non-Random Two Liquid). Finally, the partition behavior of three alkaloids (nicotine, caffeine and theobromine), used here as hydrophobicity probes, was evaluated. In all studied systems, alkaloids preferentially migrate to the IL-rich phase, with partition coefficients (K) ranging between 2.23 and complete extraction, in a single-step. Furthermore, the set of ILs investigated allowed identifying an odd-even effect in the alkaloids partitioning derived from the IL anion alkyl chain length. These results support the salting-out effect exerted by K3PO4 and favorable dispersive interactions established between the IL-rich phase-forming components and the alkaloids.

Green synthesis of acetylated maize starch in different imidazolium carboxylate and choline carboxylate ionic liquids

This work demonstrates that acetylated maize starches (AMS) with varied degree of substitution (DS, 0.26–2.63) was synthesized in ionic liquids (ILs) (imidazolium chloride, imidazolium carboxylate and choline carboxylate) at 85 °C without catalyst. The DS of AMS and reaction efficiency increased with decreasing alkyl chain length of cations or anions, while decreased as the choline cation replaced the imidazolium cation and the chloride anion replaced the acetate anion. The AMS synthesized in imidazolium-based ILs exhibited much higher hydrophobicity and thermal stability than the native starch. Rheological properties of ILs and ATR-FTIR analysis of acetic anhydride/ILs mixtures indicated that a shorter alkyl side chain or the combination of an imidazolium cation and an acetate anion gave ILs lower viscosities and weaker interactions between acetic anhydride molecules, which favored the acetylation of starch. These findings provide insights into the design of green processes to modify starch and the application of acetylated starch.

Ion Dissociation in Ionic Liquids and Ionic Liquid Solutions

The extent to which cations and anions in ionic liquids (ILs) and ionic liquid solutions are dissociated is of both fundamental scientific interest and practical importance because ion dissociation has been shown to impact viscosity, density, surface tension, volatility, solubility, chemical reactivity, and many other important chemical and physical properties. When mixed with solvents, ionic liquids provide the unique opportunity to investigate ion dissociation from infinite dilution in the solvent to a completely solvent-free state, even at ambient conditions. The most common way to estimate ion dissociation in ILs and IL solutions is by comparing the molar conductivity determined from ionic conductivity measurements such as electrochemical impedance spectroscopy (EIS) (which measure the movement of only the charged, i.e., dissociated, ions) with the molar conductivity calculated from ion diffusivities measured by pulse field gradient nuclear magnetic resonance spectroscopy (PFG-NMR, which gives movement of all of the ions). Because the NMR measurements are time-consuming, the number of ILs and IL solutions investigated by this method is relatively limited. We have shown that use of the Stokes-Einstein equation with estimates of the effective ion Stokes radii allows ion dissociation to be calculated from easily measured density, viscosity, and ionic conductivity data (ρ, η, λ), which is readily available in the literature for a much larger number of pure ILs and IL solutions. Therefore, in this review, we present values of ion dissociation for ILs and IL solutions (aqueous and nonaqueous) determined by both the traditional molar conductivity/PFG-NMR method and the ρ, η, λ method. We explore the effect of cation and anion alkyl chain length, structure, and interaction motifs of the cation and anion, temperature, and the strength of the solvent in IL solutions.

Study of the toluene absorption capacity and mechanism of ionic liquids using COSMO-RS prediction and experimental verification

As green solvents, ionic liquids (ILs) are quite suitable for the absorption of volatile organic compounds (VOCs) such as benzene and its homologues. However, solvent selection is the key to the VOC absorption process. In the present study, a rapid solvent screening tool, Conductor-like Screening Model for Real Solvents (COSMO-RS), was used to predict the solubility of toluene in 816 ILs. The effects of four structure characters, namely, the type and alkyl chain length of the cations and anions on the solubility of toluene were discussed. The following conclusions were drawn from the results: (1) ILs with pyrrolidinium-based cations showed better solubility than pyridinium- and imidazolium-based ones. (2) The solubility of toluene in PF6-based ILs increased with the increasing alkyl chain length, while its solubility in Ac-based ILs exhibited the opposite trend. (3) Toluene showed greater solubility in Cl-based ILs than those based on other anions. (4) The solubility of toluene increased with the anion alkyl chain length. Ac-based ILs were chosen as the most promising potential solvents, and further studied to determine the relationship between various interaction energy parameters and toluene solubility. The results showed that the misfit energy played a dominant role during the absorption process. Furthermore, several ILs were selected for experimental verification of the predicted solubility behavior using liquid and gaseous toluene. The results demonstrated that COSMO-RS could be used to semi-quantitatively and qualitatively predict the solubility of toluene, and this model had promising prospects in screening ILs for VOCs absorption. In summary, this study provided a fundamental basis and practical data for the control and treatment of VOCs.

Chitin-glucan complex – Based biopolymeric structures using biocompatible ionic liquids

This work explores the novelty of dissolving chitin-glucan complex (CGC), from two fungal strains, Komagataella pastoris (CGCP) and Aspergillus niger (CGCKZ) (KiOnutrime-CG™), using biocompatible ionic liquids (ILs). Three cholinium-based ILs were tested, choline acetate, choline propionate and choline hexanoate. Although all tested ILs resulted in the dissolution of the co-polymer at a concentration of 5 % (w/w), distinct polymeric structures, films or gels, were obtained from CGCP and CGCKZ, respectively. CGCP films were dense, flexible and elastic, with high swelling capacity (> 200 %). The IL anion alkyl chain length influenced the polymeric structures’ properties, namely, the CGCP films elongation at break and swelling degree. CGCKZ resulted in weak gels. For both polymeric structures, exposure to the ILs under the dissolution conditions caused significant changes in the co-polymers’ chemical structure, namely, reduction of their glucan moiety and reduction of the degree of acetylation, thus yielding chitosan-glucan complexes (ChGC) enriched in glucosamine (53.4 ± 0.3–60.8 ± 0.3 %).

Designing silica xerogels containing RTIL for CO2 capture and CO2/CH4 separation: Influence of ILs anion, cation and cation side alkyl chain length and ramification

CO2 separation from natural gas is considered to be a crucial strategy to mitigate global warming problems, meet product specification, pipeline specs and other application specific requirements. Silica xerogels (SX) are considered to be potential materials for CO2 capture due to their high specific surface area. Thus, a series of silica xerogels functionalized with imidazolium, phosphonium, ammonium and pyridinium-based room-temperature ionic liquids (RTILs) were synthesized. The synthesized silica xerogels were characterized by NMR, helium pycnometry, DTA-TG, BET, SEM and TEM. CO2 sorption, reusability and CO2/CH4 selectivity were assessed by the pressure-decay technique. Silica xerogels containing IL demonstrated advantages compared to RTILs used as separation solvents in CO2 capture processes including higher CO2 sorption capacity and faster sorption/desorption. Using fluorinated anion for functionalization of silica xerogels leads to a higher affinity for CO2 over CH4. The best performance was obtained by SX- [bmim] [TF2N] (223.4 mg CO2/g mg/g at 298.15 K and 20 bar). Moreover, SX- [bmim] [TF2N] showed higher CO2 sorption capacity as compared to other reported sorbents. CO2 sorption and CO2/CH4 selectivity results were submitted to an analysis of variance and the means compared using Tukey's test (5%).

Two fatty acid anion-based ionic liquids - part I: Physicochemical properties and tribological behavior as neat lubricants

Two new ionic liquids ([N 6,6,6,6 ][C 8:0 ] and [N 6,6,6,6 ][C 16:0 ]) synthetized from fatty acids through a salt metathesis reaction were both characterized from a physicochemical and tribological point of view. Density, viscosity, corrosion activity and thermal stability tests were performed before making tribological tests under ball-on-disc both unidirectional (with fixed and variable slide-to-roll ratio) and reciprocating configuration. The main results of this work were the following: the longer the length of the alkyl chain of the anion the lower both viscosity and density and higher both viscosity index and thermal stability; these ionic liquids (ILs) are not corrosive; the [N 6,6,6,6 ][C 16:0 ] behaved better changing from elastohydrodynamic to mixed lubrication regime at lower speeds; their antiwear behavior at high load seems depend on their viscosity (for tests made at room temperature) and thermal stability and IL-surface interaction (for tests made at high temperature). • Two fatty acids anion-based ionic liquids were obtained and tribologically studied. • These fatty acids anion-based ionic liquids are not corrosive. • The anion alkyl chain length determines viscosity, thermal and tribological behavior.

Fatty acid-derived ionic liquids as renewable lubricant additives: Effect of chain length and unsaturation

Fatty acid-derived ionic liquids (FAILs) are synthesized and then demonstrated as the environmentally-friendly additive to mineral lube base oil for enhancement of lubrication properties. Unlike most of the conventional ionic liquids, FAILs exhibited good miscibility with non-polar mineral lube base oil. The quaternary structure of tetrabutylammonium (TBA) cation, diffused positive charge on the cationic center due to +I effect of alkyl chains, and the alkyl chain of fatty acid anion collectively facilitates the miscibility of FAILs in the mineral lube base oil. Experimental results revealed that 1% FAILs could significantly reduce the friction (16–27%) and wear (9–15%) of lube base oil. The viscosity of these ionic liquids is found to be governed by alkyl chain-length and unsaturation of fatty acid anions, and it exhibited a linear correlation with the coefficient of friction. The elemental mapping of worn surfaces on aluminium disc suggested the formation of ionic liquids-derived tribochemical film, which is accounted for protection of tribo-interfaces to reduce the wear and friction. The FAILs being halogen-free, environment-friendly, having an excellent affinity towards engineering surfaces, and good miscibility with non-polar hydrocarbon lubricants, promised the immense potential for tribological applications.

Effects of cholinium-based ionic liquids on Aspergillus niger lipase: Stabilizers or inhibitors.

Lipases are well-known biocatalysts used in several industrial processes/applications. Thus, as with other enzymes, changes in their surrounding environment and/or their thermodynamic parameters can induce structural changes that can increase, decrease, or even inhibit their catalytic activity. The use of ionic compounds as solvents or additives is a common approach for adjusting reaction conditions and, consequently, for controlling the biocatalytic activity of enzymes. Herein, to elucidate the effects of ionic compounds on the structure of lipase, the stability and enzymatic activity of lipase from Aspergillus niger in aqueous solutions (at 0.05, 0.10, 0.50, and 1.00 M) of six cholinium-based ionic liquids (cholinium chloride [Ch]Cl; cholinium acetate ([Ch][Ac]); cholinium propanoate ([Ch][Prop]); cholinium butanoate ([Ch][But]); cholinium pentanoate ([Ch][Pent]); and cholinium hexanoate ([Ch][Hex])) were evaluated over 24 hr. The enzymatic activity of lipase was maintained or enhanced in the lower concentrations of all the [Ch]+ -ILs (below 0.1 M). [Ch][Ac] maintained the biocatalytic behavior of lipase, independent of the IL concentration and incubation time. However, above 0.1 M, [Ch][Pent] and [Ch][Hex] caused complete inhibition of the catalytic activity of the enzyme, demonstrating that the increase in the anionic alkyl chain length strongly affected the conformation of the lipase. The hydrophobicity and concentration of the [Ch]+ -ILs play an important role in the enzyme activity, and these parameters can be controlled by adjusting the anionic alkyl chain length. The inhibitory effects of [Ch][Pent] and [Ch][Hex] may be of great interest to the pharmaceutical industry to induce pharmacological inhibition of gastric and pancreatic lipases.

Effect of hydrophobicity and H-bonding abilities of ions on osmotic coefficients of aqueous diethylammonium based protic ionic liquid solutions at 298.15 K

The osmotic and activity coefficients of aqueous solutions of diethylammonium based protic ionic liquids (PILs) were determined experimentally using vapor pressure osmometry in the concentration range of (~0.02 to ~0.5) mol·kg−1 at 298.15 K. Osmotic coefficient data show positive deviation from Debye-Hückel limiting law for all the studied PILs. Also a minimum in osmotic coefficient data was observed at higher concentrations and is explained in terms of ion-pair formation. Data of experimental osmotic coefficient were used to obtain activities (aw) and activity coefficients (γ1) of water, mean molal activity coefficient (γ±) of PILs and excess Gibbs free energy change (ΔGE) due to mixing. Observed variations in osmotic coefficients data were explained in terms of hydrophobicity as well as H-bonding. The data of osmotic and activity coefficients were further subjected to analysis through Pitzer ion-interaction model to get an information of ion-ion and ion-solvent interaction to understand ion-pairing, ion hydration and hydrophobic effects in aqueous solutions of PILs. For this, Pitzer ion interaction parameters β(0) and β(1) were estimated and compared with literature data available for other relevant systems. Finally, the results are interpreted in terms ion-ion, ion-solvent interaction along with effect of hydrophobicity on ion-pairing and further discussed the effect of alkyl chain length of anions on solvation behavior of protic ionic liquids in aqueous solutions.

Tribological properties of ionic liquids for steel/aluminum, steel/copper and steel/Si3N4 ceramic contacts under boundary lubrication

PurposeThe purpose of this paper is to study the influence of alkyl chain length and kind of anions of ionic liquids on the tribological properties with different materials as friction pairs (steel-aluminum, steel-copper and steel-Si3N4 ceramic).Design/methodology/approachTribological properties were evaluated by an optimol-SRV-IV reciprocation friction tester with a ball-on-block configuration at room temperature and high temperature, respectively. Friction-reducing and anti-wear properties of the ionic liquids for steel/aluminum, steel/copper and steel/ceramic contacts were evaluated on the ball-on-block reciprocating UMT-2MT tribometer. The morphologies of the worn surfaces were observed by a scanning electron microscope. The chemical states of several typical elements on the worn surfaces were examined by X-ray photoelectron spectroscopy.FindingsBoth the alkyl chain length and kind of anion influence the tribological properties of ionic liquids, especially for the length of alkyl chains. With the increase of alkyl chain length, the load carrying capacity of ionic liquids is improved at both room temperature and high temperature, and the friction reducing and antiwear behaviors are also significantly enhanced.Research limitations/implicationsThe paper presents potentially useful and highly efficient lubricants.Practical implicationsOwing to their good friction-reducing and wear resistance properties, these ionic liquids are promising candidates for versatile applications.Originality/valueThis work might provide a promising research direction for design and application of ionic liquids as lubricants.

Thermophysical properties and ecotoxicity of new nitrile functionalised protic ionic liquids

In this present research, five nitrile functionalised imidazolium based protic ionic liquids (PILs) by varying alkyl chain length of anions were synthesized. The synthesized ILs were characterized with nuclear magnetic resonance spectroscopy (NMR) and elemental analyser (CHNS). Various thermophysical properties such as refractive index, density, viscosity and thermal stability were measured over wide temperature range. From the density experimental data, different volumetric properties were estimated using well established empirical equations. Moreover, the effect of temperature and increase of alkyl substitutions attached to anion has been evaluated for the studied properties. The toxicity of the synthesized ILs has been assessed against three human pathogenic bacteria i.e., Aeromonas hydrophila A97 (AH), Escherichia coli E149 (EC), and Staphylococcus aureus S244 (SA) in light to identify the influence of increasing alkyl substitution of the anion moiety on the overall toxicity of PILs.