Rashi Gusain

Halogen-Free Bis(imidazolium)/Bis(ammonium)-Di[bis(salicylato)borate] Ionic Liquids As Energy-Efficient and Environmentally Friendly Lubricant Additives

Bis(imidazolium)- and bis(ammonium)-di[bis(salicylato)borate] ionic liquids with variable alkyl chain and cyclic ring structures, were synthesized and then evaluated them as potential lubricant additives. The copper strip test results revealed noncorrosive properties of these ionic liquids. Introduction of halogen content in bis(imidazolium) ionic liquid by replacement of bis(salicylato)borate (BScB) anion with hexafluorophosphate (PF6(-)), severely corroded the copper strip. Thermogravimetric results showed that bis(imidazolium) ionic liquids exhibited higher thermal stability than bis(ammonium) ionic liquids owing to compact structure provided by imidazolium rings, higher intermolecular interactions, smaller free volume and low steric hindrance. The lubrication properties of these ionic liquids as additives to synthetic lubricant poly(ethylene) glycol (PEG 200) were evaluated for steel balls. Results showed that bis(ammonium)- and bis(imidazolium)-(BScB)2 ionic liquids as additives significantly reduced both friction coefficient and wear of PEG 200. The structure of cations, particularly the variation in substituted alkyl chain length monitored the degree of reduction in friction and wear. The excellent lubrication properties were attributed to the formation of adsorbed tribo-thin film and tribochemical product during the tribo-contact. Being halogen-, phosphorus-, and sulfur-free, these ionic liquids (a) protects contact surfaces from tribo-corrosive events, (b) reduces the friction and wear, and (c) keep environment green and clean.

Alkyl-chain-grafted hexagonal boron nitride nanoplatelets as oil-dispersible additives for friction and wear reduction.

Hexagonal boron nitride (h-BN), an isoelectric analogous to graphene multilayer, can easily shear at the contact interfaces and exhibits excellent mechanical strength, higher thermal stability, and resistance toward oxidation, which makes it a promising material for potential lubricant applications. However, the poor dispersibility of h-BN in lube base oil has been a major obstacle. Herein, h-BN powder was exfoliated into h-BN nanoplatelets (h-BNNPs), and then long alkyl chains were chemically grafted, targeting the basal plane defect and edge sites of h-BNNPs. The chemical and structural features of octadecyltriethoxysilane-functionalized h-BNNPs (h-BNNPs-ODTES) were studied by FTIR, XPS, XRD, HRTEM, and TGA analyses. The h-BNNPs-ODTES exhibit long-term dispersion stability in synthetic polyol ester lube base oil because of van der Waals interaction between the octadecyl chains of h-BNNPs-ODTES and alkyl functionalities of polyol ester. Micro- and macrotribology results showed that h-BNNPs-ODTES, as an additive to synthetic polyol ester, significantly reduced both the friction and wear of steel disks. Elemental mapping of the worn area explicitly demonstrates the transfer of h-BNNPs-ODTES on the contact interfaces. Furthermore, insight into the lubrication mechanism for reduction in both friction and wear is deduced based on the experimental results.

Halogen-free imidazolium/ammonium-bis(salicylato)borate ionic liquids as high performance lubricant additives

Halogen-free bis(salicylato)borate anion based ionic liquids having imidazolium and ammonium cations, were designed, synthesized, characterized and then evaluated as potential lubricant additives. Owing to the high polarity, high London dispersive forces and high rigidity associated with the bulk size and ring structure of the bis(salicylato)borate anion, these ionic liquids possess very high viscosities. The interaction of these ionic liquids with contact surfaces has been found to be strongly influenced by the van der Waals interactions in the ionic liquids, which increases with an increase of the alkyl chain length, particularly, for the imidazolium cations. As lubricant additives, both imidazolium and ammonium ionic liquids markedly improve the friction-reducing and anti-wear properties of PEG 200 lube base. Microstructural images and element mapping of the worn surfaces of steel balls reveal that these ionic liquids form tribo-films, which reduces both the friction and wear. Being halogen-, phosphorus-, and sulfur-free, bis(salicylato)borate ionic liquids not only protect contact surfaces from tribo-corrosive events but also keep the environment green and clean. These ionic liquids offer an environmentally friendly alternative to conventional halogenated ionic liquids being currently developed for lubricant applications.

Covalently attached graphene–ionic liquid hybrid nanomaterials: synthesis, characterization and tribological application

Hybrid nanomaterials offer task-specific functional properties besides the individual properties of their constituent materials/elements. Herein, graphene–ionic liquid (Gr–IL) hybrid nanomaterials are synthesized to integrate the friction-reducing properties of both ionic liquids and graphene nanosheets. Importantly, the remarkable mechanical strength of graphene improves the anti-wear performance, whereas covalently grafted ionic liquids facilitate the dispersion of the Gr–IL in the polyethylene glycol (PEG 200) synthetic lube base oil. Graphene, prepared by a controlled chemical approach, is used for the covalent grafting of an imidazolium ring. Three variable Gr–IL hybrid nanomaterials, containing bis(salicylato)borate (BScB), oleate (OL), and hexafluorophosphate (PF6) anions, are synthesized to control their surface properties. Detailed chemical and microstructural features of the Gr–IL hybrid nanomaterials are studied using FTIR, XPS, Raman, XRD, FESEM, and HRTEM analyses. The Gr–IL hybrid nanomaterials as lubricant additives for PEG 200 significantly reduced the friction and the wear. Further, the Gr–IL hybrid nanomaterials offer remarkably improved anti-wear properties (55–78%) compared to that of the corresponding ionic liquid (7–39%) blends in PEG 200 and this was attributed to the high mechanical strength of graphene, which protects the contact interfaces against material loss. The elemental and micro-Raman results of the worn surfaces suggested the formation of a tribo-chemical thin film composed of Gr–IL and its tribo-chemical products with steel interfaces. The BScB anion constituted Gr–BScB showed the maximum reduction in friction, whereas the OL analogue exhibited the smallest wear. This study reveals the potential of task-specific Gr–IL hybrid nanomaterials as novel additives for diversified tribological applications.

Ultrasound assisted shape regulation of CuO nanorods in ionic liquids and their use as energy efficient lubricant additives

Copper oxide nanorods (CuONR1) having a diameter of about 20–30 nm and a length of about 30–70 nm were prepared by simple chemical processing of copper salt. CuONR1 were morphologically reshaped, by sonication with 1-hexyl-3-methylimidazolium acetate and tetrabutylammonium acetate ionic liquids, to CuONR2 and CuONR3, respectively. Both CuONR2 and CuONR3, with a diameter of about 8–18 nm and a length of about 60–200 nm, exhibit high aspect ratios (length-to-breadth) compared to CuONR1. The XRD pattern reveals the monoclinic crystalline structure of CuONR1, which remains unchanged during their ultrasound treatment with ionic liquids. Dispersion stability and aspect ratio of CuO nanorods are found to play an important role in monitoring the lubrication characteristics. The results show that CuONR2 and CuONR3, stabilized by ionic liquids, exhibit excellent friction-reduction (15–43%) and improved anti-wear properties (26–43%) compared to the PEG 200 and 10W-40 engine oil. Lubricity enhancement is attributed to the synergistic effect of uninterrupted supplies of CuO nanorods under the contact surfaces and their rolling effect mechanism, which eventually leads to energy saving and prevents material loss.

Fatty acid ionic liquids as environmentally friendly lubricants for low friction and wear

Vegetable oils are environmentally-friendly, sustainable and rich source of fatty acids, and have been used as lubricants since ancient times. The carboxylic group of fatty acids interacts with metal surface and forms the tribo-chemical thin film of low shear strength under the boundary lubrication, which reduces the friction and the wear. Herein, four fatty acids having variable chain length and unsaturated sites are selected as anionic precursors to prepare the tetrabutylammonium-fatty acid ionic liquids. The preparation of these ionic liquids is confirmed by FTIR and NMR (1H and 13C) analyses. The chain length and degree of unsaturation in the fatty acid anions control the viscosity, melting temperature, crystallization temperature and latent heat of fatty acid ionic liquids. These ionic liquids as lubricants exhibited significantly lower friction (18–50%) compared to polyol ester lube base oil. Further, the degree of friction reduction is largely influenced by the structure of the constituent fatty acid anion. The oleate anion showed the best tribo-performance among all fatty acid ionic liquids being studied. The elemental mapping of worn surfaces revealed the formation of fatty acid ionic liquids constituted a tribo-chemical thin film. Being halogen-free and abundantly available sources of fatty acid precursors, these ionic liquids promise immense potential for tribological applications, where the friction and environment are of prime importance.

Halogen-free ionic liquids: effect of chelated orthoborate anion structure on their lubrication properties

In transportation vehicles, a large portion of energy is consumed to overcome friction in the engine and associated components. An efficient lubricant system has a direct impact on saving energy and material loss by reducing the friction, wear, and corrosion. Herein, halogen-free chelated orthoborate ionic liquids were designed, synthesized and then evaluated as potential lubricant additives. The effect of the orthoborate anion structure on the thermal stability, corrosion, friction, and wear properties of ionic liquids were studied. The copper strip tests revealed the non-corrosiveness of bis(mandalato)borate (BMdB), bis(salicylato)borate (BScB), and bis(malonato)borate (BMlB) anion constituted ionic liquids. Whereas, the bis(oxalato)borate (BOxB) anion, eventually developed micro-pits of corrosion owing to its lower stability and acidic nature of the decomposed product. These ionic liquids as additives to the synthetic lube base oil significantly reduced both friction and wear. The degree of friction and wear reduction was influenced by the structure of associated anions. BMdB and BScB anion constituted ionic liquids exhibited excellent thermal stability, friction-reduction, and antiwear properties, which are attributed to their compact and chemically stable structure driven by higher intermolecular interactions and rigidity of aromatic rings. The chemical analysis of tribo-interfaces suggested the formation of an ionic liquid composed tribochemical product and that enhanced the lubrication properties. Being halogen-free, these ionic liquids could be energy efficient and environmentally-friendly substitutes to the conventional friction-reducing and antiwear additives.

Tuning the band-gap of h-boron nitride nanoplatelets by covalent grafting of imidazolium ionic liquids

Imidazolium ionic liquids with three different anions, viz. bis(salicylato)borate (BScB), oleate (OL) and hexafluorophosphate (PF6), are covalently grafted on h-boron nitride nanoplatelets (h-BNNPs) to probe the shifts in the band gap energy. The grafting of ionic liquids on h-BNNPs was confirmed by FTIR, XPS, TGA and EDX analyses, whereas XRD and HRTEM results suggested that the crystalline and layering structure of h-BNNPs remained intact after covalent grafting of ionic liquids. The characteristic band gap energy of h-BNNPs (5.9 eV) was reduced to 5.78, 5.25 and 5.00 eV in h-BNNPs-OL, h-BNNPs-PF6 and h-BNNPs-BScB, respectively. The band gap of h-BNNPs-ILs is controlled by charge transfer between the ionic liquids and h-BNNPs, and exhibited strong correlation with the chemical structure of the associated anion in h-BNNPs-ILs.

Antimicrobial and lubrication properties of 1-acetyl-3-hexylbenzotriazolium benzoate/sorbate ionic liquids

Ionic liquids exhibit immense potential for a wide range of applications including biotechnology, medicinal chemistry and lubrication. Herein, 1-acetyl-3-hexylbenzotriazolium cation-based ionic liquids having benzoate and sorbate anions are prepared by chemical derivatization of benzotriazole. The antimicrobial activities of these ionic liquids are studied using the Escherichia coli and Rhodococcus erythropolis bacterial cultures and we monitored their growth inhibition property. Further, the biostatic properties are evaluated by the kinetic growth rate inhibition method. These ionic liquids exhibited improved antimicrobial activities compared to their precursors: benzotriazole, sodium benzoate and potassium sorbate. Furthermore, these ionic liquids as an additive to polyol lube base oil improved the lubrication property by reducing the friction and wear characteristics. Microscopic images along with elemental mapping of worn surfaces confirmed the formation of an ionic liquid-constituted tribo-chemical thin film, which protects the contact surfaces against the undesirable wear and reduces the friction.

Microtribological properties of a spin-coated thin film of 1-butyl-3-(propyltrimethoxysilane)imidazolium bis(mandelato)borate ionic liquid

A thin film of 1-butyl-3-(propyltrimethoxysilane)imidazolium bis(mandelato)borate (BPtmSiIm-BMdB) ionic liquid was prepared by spin coating on a silicon surface. XPS results suggested the covalent interaction between trimethoxy groups of BPtmSiIm-BMdB ionic liquid and hydroxyl functionalities of the silicon surface, and afforded a good quality thin film. The microtribological properties of the BPtmSiIm-BMdB thin film were probed under the mean Hertzian contact stress of 0.29–0.53 GPa. The BPtmSiIm-BMdB thin film exhibited significantly low and steady friction (μ = 0.06 to 0.10) at variable loads compared to bare silicon (μ = 0.6). The low coefficient of friction and remarkable wear-resistivity of the BPtmSiIm-BMdB thin film were collectively attributed to (a) strong adherence of ionic liquid on the silicon surface, (b) a layered structure of the ionic liquid driven by coulombic interactions, (c) a rigid and compact structure of the chelated bis(mandelato)borate anion, (d) tribo-induced deposition of ionic liquid on the counter steel ball and (e) the presence of flowable fraction of the ionic liquid with a self-replenishment property. This study demonstrates a good prospect for ionic liquid thin films, which have a stable and good foundation on the underlying surface.