Increase In Concentration Of Ionic Liquids Research Articles

Deciphering aggregation behavior and thermodynamic properties of anionic surfactant sodium hexadecyl sulfate in aqueous solutions of ionic liquids [C5mim][Br] and [C6mim][Br

The present work aims to study the interactions of cationic imidazolium based ionic liquids i.e. 1-alkyl-3-methylimidazolium bromide ([Cnmim][Br], where n = 5 &6) with anionic surfactant sodium hexadecyl sulfate (SHS) in aqueous media employing the various techniques such as conductivity measurement, fluorescence spectroscopy, UV–visible spectroscopy and FT-IR spectroscopy. The temperature dependence of critical micelle concentration (CMC) determined using conductivity measurements at temperatures (298.15, 303.15 and 308.15) K at different concentrations (0.02, 0.05 and 0.1) wt. %, of ionic liquids (ILs) in aqueous medium was used to calculate the various thermodynamic parameters of micellization such as, standard free energy of micellization (ΔGm0), standard enthalpy of micellization (ΔHm0), and standard entropy of micellization (ΔSm0). Further, fluorescence and UV–Visible spectroscopy have been utilized to confirm the CMC values obtained from conductivity measurements, which were found to be in good agreement. A continuous increment in CMC value was observed with the increase in concentration of ILs as well as in temperature. Further FT-IR Spectroscopic studies have been done to demonstrate the structural alterations occurring in the respective mixtures.

Tribological performance and degradation of 1‐n‐butyl‐1‐methylpyrrolidinium methylsulfate ionic liquid in glycerol as lubricant for steel‐steel sliding contacts

AbstractThe ionic liquid (IL) 1‐n‐butyl‐1‐methylpyrrolidinium methylsulfate was studied as additive for glycerol in steel‐steel contacts. The mixtures were evaluated in different IL concentrations with a reciprocating sliding tribometer in a ball‐on‐disc configuration under elastohydrodynamic and boundary conditions at room temperature and 100°C, respectively. At room temperature, friction and wear were mainly determined by the high viscosity of glycerol; hence, little differentiation was found. At 100°C, surface smoothening resulted in decrease of friction and wear with increase of IL concentration, which indicates corrosion as dominant part of the lubricating mechanism. A 0.6‐wt% IL turned out as best performing mixture regarding tribological behaviour and additive efficiency. Methylsulfate is reduced to sulphide when in contact with the steel surface. Methylsulfate reacts with glycerol to give glyceryl sulfate already during mixing as revealed by mass spectrometry. Acorrdingly, after triboexperiments, ions composed of sulfate, iron, and glycerol were identified.

Mechanism of graphene formation by graphite electro-exfoliation in ionic liquids-water mixtures

Graphene was produced from graphite electrode by exfoliation in ionic liquid. The influences of process parameters such as ionic liquid concentration, electrolysis potential and the type of anions in the ionic liquid on the production of graphene were studied, and a new mechanism is proposed. The results show that the increase of ionic liquid concentration is beneficial for the formation of graphene, and it is easier to produce graphene by increasing the applied voltage. Ionic liquids anions have great effect on the production of graphene. Both graphite anode and graphite cathode can be modified to graphene during electrolysis. Gases formed inside of the electrode play an important role for the production of graphene, while ionic liquids serve to accelerate the switching rate of graphite to graphene.

Structure and ionic conductivity of ionic liquid embedded PEO- LiCF3SO3 polymer electrolyte

In this paper we have reported electrical and other physical properties of polyethylene oxide (PEO) - LiCF3SO3 polymer electrolytes embedded with 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ionic liquid. The addition of the ionic liquid to PEO- LiCF3SO3 electrolyte increases the amorphous phase content considerably and decreases the glass transition temperature. The relative amounts of different ionic species present in these electrolytes have been determined. It is observed that the fraction of free anions increase with the increase of ionic liquid concentration, whereas the fraction for ion pairs and aggregates show a decreasing trend under the same condition. The ionic conductivity of the PEO- LiCF3SO3 polymer electrolyte embedded with ionic liquid is higher than that of the PEO- LiCF3SO3 electrolyte. The ionic conductivity shows a transition around 323 K. The ionic conductivity above 323 K exhibits Arrhenius behavior with an activation energy, which decreases with the increase of ionic liquid concentration. However, below 323 K the conductivity shows Vogel–Tamman–Fulcher (VTF) type behavior.

Effect of ionic liquids on the different hierarchical order of type I collagen

The effect of ionic liquids (ILs) on proteins has been gaining huge interest due to easy tunability of cation and anion for generating the desired effect. This study explores the effect of alkyl imidazolium chloride ILs on collagen at molecular, inter-fibrillar and skin matrix level. Circular dichroic studies reveal that at the molecular level, the secondary structure of collagen was not affected by imidazolium ILs and there was no change in thermal stability as well. However, collagen at the inter-fibrillar level behaved differently. With increase in concentration of ILs, remarkable decrease in thermal stability of rat tail tendon (RTT) collagen fibers with marginal swelling effect was seen. SEM micrographs of skin matrix treated with IL show opening up of pores. This kind of exquisite behavior of ILs at different hierarchal order of collagen indicates that ILs are endowed with potential lyotropic action, which can be judiciously employed for biomedical applications.

Spectroscopic studies on the interactions between imidazolium chloride ionic liquids and bovine serum albumin

The binding of three imidazolium chloride ionic liquids (ILs) with bovine serum albumin (BSA) were investigated by UV absorption spectra, fluorescence spectra and synchronous fluorescence spectra. The results showed that the UV absorption of the BSA was red-shift, and intensity of UV absorption declined with the increase in concentration of ILs. According to fluorescence spectra, fluorescence quenching of the BSA was happened with ILs added, and the main reason is static quenching. The study of synchronous fluorescence spectra indicated that ILs interacted with tryptophan (Trp) and tyrosine (Tyr) residues, changed the structure and the internal hydrophobic conformation of BSA. The binding constant K and the numbers of binding sites n were obtained by Stern–Volmer equation. For [Bmim]Cl, K=16.12Lmol−1, n was 0.64; for [Hmim]Cl, K=31.48Lmol−1, n was 0.70; for [Omim]Cl, K=355.22Lmol−1, n was 0.99. The binding strength of ILs with BSA is expected to show the trend with the length of carbon chain, [Bmim]Cl<[Hmim]Cl<[Omim]Cl.

β-Galactosidase activity in mixed micelles of imidazolium ionic liquids and sodium dodecylsulfate: A sequential injection kinetic study

An automated methodology for the kinetic study of β-galactosidase activity in sodium dodecylsulfate (SDS)/ionic liquid (IL) mixed micelles was developed. The main objective of the work was the evaluation of mixed micelles as reaction media for the industrial synthesis of glyco-oligossacharides. Enzyme activity was evaluated by means of a model reaction with the fluorescent substrate 4-methylumbelliferyl-α-d-galactopyranoside (MUG). The assay was implemented in a sequential injection analysis (SIA) system and enzyme activity was studied in SDS/bmim [BF4] and SDS/hmim [Cl] mixed micelles with variable concentrations of both components. In order to perform a critical evaluation of the obtained results, CMC and average micellar size of SDS/hmim [Cl] mixed micelles were evaluated by fluorescence and dynamic light scattering, respectively. In the micelle characterization assays it was observed that the CMC of the mixed micelles increased with hmim [Cl] concentration up to 1molL−1. In the presence of higher IL concentrations there were no evidences of micelle formation. Regarding micellar size, it was maximum for an IL concentration of 0.09molL−1. The kinetic assays evidenced that SDS/bmim [BF4] and SDS/hmim [Cl] mixed micellar systems can led to an increase of enzyme activity. This increase is dependent on the variation of the average micellar size that occurs with the increase of IL concentration up to 0.09molL−1. It was also noticed that the most promising systems are those incorporating SDS and IL in concentrations under 50mmolL−1 and 0.5molL−1, respectively. These results evidenced that the studied ILs can modify the physico-chemical properties of the surfactant solution in a favourable way regarding β-galactosidase activity being an important achievement for the future implementation of industrial processes catalyzed by this enzyme, mainly the synthesis of glyco-oligossacharides. Indeed, surfactant/IL mixed micelles proved to be an interesting alternative to conventional organic solvents in this field enabling the implementation of the processes in a relatively hydrophobic media with enhanced enzyme activity.

Effect of ionic liquid, 1-octyl-3-methylimidazolium bromide on the thermophysical properties of aqueous d-glucose solutions at 298.15 K

Thermophysical properties including densities, viscosities, refractive indices, and molar conductivities for ternary systems containing d-glucose, ionic liquid {1-octyl-3-methylimidazolium bromide ([OMIm]Br)} and water have been measured at 298.15 K. The density and viscosity data have been used to calculate apparent molar volumes, V ϕ , standard partial molar volumes (which equal in value with infinite dilution apparent molar volume), V ϕ 0 , transfer volumes, Δ tr V ϕ 0 , of d-glucose from water to aqueous [OMIm]Br solutions and viscosity B-coefficients. An increase in the values of V ϕ 0 , Δ tr V ϕ 0 and viscosity B-coefficient was observed with increase of ionic liquid concentration. Limiting molar conductivities, Λ 0, and ion association constants, K a, of [OMIm]Br in aqueous d-glucose solutions were estimated from low concentration chemical model (lcCM). Molar refractions, R D, were calculated from refractive index, n D, measurements using Lorentz–Lorenz equation. All of these parameters were discussed in terms of the different solute-solvent interactions occurring between d-glucose and ionic liquid.