Ionic Liquid-based Surfactants Research Articles

Effects of conventional and ionic liquid-based surfactants and sodium tetraborate on interfacial tension of acidic crude oil

The application of a new class of surfactants such as ionic liquids (ILs) compared with the conventional surfactants and their interactions with each other concomitant and alkaline under salinities is not well examined based on the best knowledge of the authors. So, the current work focused on the impact of sodium lauryl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS), 1-dodecyl 3-methyl imidazolium chloride (C12mim][Cl]), 1-octadecyl 3-methyl imidazolium chloride ([C18mim][Cl]) in the presence and absence of alkali namely sodium tetraborate known as borax (Na2B4O7) on the IFT variation while the salinity was changed 0–82,000 ppm (ionic strength of 0–1.4 M). The results showed the positive impact of salinity on the pH reduction and reduced the alkaline effect for pH reduction. Also, the measurements showed that the presence of surfactant reduces the role of alkaline for pH variation as it moved from 9.2 to 6.63 for the solution prepared using SLS and SDBS. The measured IFT values showed that not only alkali has a significant impact as it combined with SLS and SDBS due to a desired synergy between these chemicals, it can reduce the critical micelle concentration (CMC) for the SDBS from 1105 to 852 ppm and much higher for [C12mim][Cl].

Investigation on the interactions of resinous and asphaltenic synthetic oils and silicon oxide nanoparticles stabilized by different ionic liquid-based surfactants: interfacial tension and wettability alteration studies

The effects of the main components of crude oil, especially resin and asphaltene fractions, are essential concerns for efficient enhanced oil recovery (EOR) processes, especially during chemical injection processes. This importance comes from the nature of these two fractions which can act as surface active agents with undeniable effects on the used chemical for interfacial tension (IFT) reduction and wettability alteration. In this way, the effect of silicon oxide nanoparticles (SiO2-NPs) concomitant with two ionic liquids (ILs), namely 1-dodecyl-3-methyl imidazolium chloride ([C12mim][Cl]) and 1-octadecyl-3-methyl imidazolium chloride ([C18mim][Cl]), is investigated on the wettability alteration and IFT reduction using synthetic oils prepared by dissolving the extracted resin and asphaltene fractions with a concentration of 1–5 wt%. The measurements reveal that the effect of resin fraction is less than the asphaltene fraction for IFT reduction and wettability alteration. The sole presence of resin fraction reduces the IFT from 35.3 to 28.3 mN/m as the concentration is increased from 1 to 5 wt%, while a similar increase in the asphaltene fraction concentration reduces the IFT from 35.5 to 19.1 mN/m. Besides, the results reveal that the presence of [C12mim][Cl] in the range of 0–1000 ppm leads to a reduction in IFT from its maximum value of 35.3 to 0.81 mN/m, while in the case of [C18mim][Cl] with similar concentration variation, IFT is reduced from 35.3 to 0.7 which means the better effect of IL with longer chain length on the IFT reduction. Further analysis revealed that the effect of asphaltene fraction on the IFT is higher than resin fraction since the minimum IFT value was observed for [C18mim][Cl] with the value of 0.58 mN/m, while the contact angle (CA) values revealed revers effect for asphaltene fraction compared with the resin fraction. In general, regardless of the used IL, it seems that ILs leading to better wettability conditions which are crucial for EOR purposes and even better IFT values that can mobilize the trapped oil toward production points. Besides, further measurements revealed a positive effect of SiO2-NPs concomitant with the ILs to move the wettability toward the strongly water-wet condition with CA values of 29.2° and 28.3° for SiO2-NPs concentration of 1000 ppm and 1000 ppm of concentration for [C12mim][Cl] and [C18mim][Cl], respectively, for resinous synthetic oil (RSO) (5 wt%) while no meaningful effect regarding the SiO2-NPs presence at the different concentrations (100–2000 ppm) is found on the IFT reduction. A similar trend is observed for asphaltenic synthetic oil (5 wt%)/aqueous solution (SiO2-NPs with a concentration of 1000 ppm + ILs with a concentration of 1000 ppm) which reduces the CA to 26.3° and 37.8° for [C12mim][Cl] and [C18mim][Cl]), respectively.

Gemini ionic liquid-based surfactants: efficient synthesis, surface activity, and use as inducers for the fabrication of Cu2O nanoparticles.

Discovery of green and novel synthetic routes for nanoparticles (NPs) has drawn a lot of interest due to the distinct nano size and unusual features as well as applications of such particles. Ionic liquid-based surfactants (ILBSs) and gemini ionic liquid-based surfactants (GILBSs) have become some of the best choices to be used as inducers or dispersing agents for the fabrication of nanoparticles. This work involves the synthesis, spectroscopic characterization, and surface property evaluation of three novel GILBSs (4a-c), which incorporate the imidazolium cation as the polar head with an ethylene spacer. The simple synthetic route includes, first, alkylating imidazole-N1 with the as-prepared fatty alkyl chloroacetates followed by quaternization of two equivalents of imidazole-N2 with ethylene dibromide. Investigations into the compounds' surface characteristics and thermodynamic parameters were carried out. The prepared GILBSs, 4a-c, were then used as inducers at various concentrations for the preparation of cuprous oxide nanoparticles. The size and shape of the produced NPs were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis in each case to study the effect of concentration on the NP morphology and to determine the best concentration for the NPs fabrication. The XRD patterns of the produced Cu2O NPs contain distinguishable peaks, which refer to crystalline Cu2O. Also, TEM images show that the obtained Cu2O is present in form of well dispersed nanorod particles with sizes about 55 and 23 nm at concentrations of 60 and 200 ppm, respectively.

Ionic liquid-based surfactants as microreactors for dyes sequestration and drug encapsulation

Ionic liquid-based surfactants as microreactors for dyes sequestration and drug encapsulation

Biocompatible Solvents and Ionic Liquid-Based Surfactants as Sustainable Components to Formulate Environmentally Friendly Organized Systems.

In this review, we deal with the formation and application of biocompatible water-in-oil microemulsions commonly known as reverse micelles (RMs). These RMs are extremely important to facilitate the dissolution of hydrophilic and hydrophobic compounds for biocompatibility in applications in drug delivery, food science, and nanomedicine. The combination of two wisely chosen types of compounds such as biocompatible non-polar solvents and ionic liquids (ILs) with amphiphilic character (surface-active ionic liquids, SAILs) can be used to generate organized systems that perfectly align with the Green Chemistry concepts. Thus, we describe the current state of SAILs (protic and aprotic) to prepare RMs using non-polar but safe solvents such as esters derived from fatty acids, among others. Moreover, the use of the biocompatible solvents as the external phase in RMs and microemulsions/nanoemulsions with the other commonly used biocompatible surfactants is detailed showing the diversity of preparations and important applications. As shown by multiple examples, the properties of the RMs can be modified by changes in the type of surfactant and/or external solvents but a key fact to note is that all these modifications generate novel systems with dissimilar properties. These interesting properties cannot be anticipated or extrapolated, and deep analysis is always required. Finally, the works presented provide valuable information about the use of biocompatible RMs, making them a green and promising alternative toward efficient and sustainable chemistry.

Ionic Liquid-Based Surfactants: Recent Advances in Their Syntheses, Solution Properties, and Applications.

The impetus for the expanding interest in ionic liquids (ILs) is their favorable properties and important applications. Ionic liquid-based surfactants (ILBSs) carry long-chain hydrophobic tails. Two or more molecules of ILBSs can be joined by covalent bonds leading, e.g., to gemini compounds (GILBSs). This review article focuses on aspects of the chemistry and applications of ILBSs and GILBSs, especially in the last ten years. Data on their adsorption at the interface and micelle formation are relevant for the applications of these surfactants. Therefore, we collected data for 152 ILBSs and 11 biamphiphilic compounds. The head ions of ILBSs are usually heterocyclic (imidazolium, pyridinium, pyrrolidinium, etc.). Most of these head-ions are also present in the reported 53 GILBSs. Where possible, we correlate the adsorption/micellar properties of the surfactants with their molecular structures, in particular, the number of carbon atoms present in the hydrocarbon “tail”. The use of ILBSs as templates for the fabrication of mesoporous nanoparticles enables better control of particle porosity and size, hence increasing their usefulness. ILs and ILBSs form thermodynamically stable water/oil and oil/water microemulsions. These were employed as templates for (radical) polymerization reactions, where the monomer is the “oil” component. The formed polymer nanoparticles can be further stabilized against aggregation by using a functionalized ILBS that is co-polymerized with the monomers. In addition to updating the literature on the subject, we hope that this review highlights the versatility and hence the potential applications of these classes of surfactants in several fields, including synthesis, catalysis, polymers, decontamination, and drug delivery.

On the effects of head-group volume on the adsorption and aggregation of 1-(n-hexadecyl)-3-Cm-imidazolium bromide and chloride surfactants in aqueous solutions

The effects of the length of alkyl side chain (Cm) of ionic liquid-based surfactants (ILBSs) on their adsorption at the water/air interface, and aggregation in aqueous solutions were investigated for the series 1-(n-hexadecyl)-3-Cm-imidazolium bromides and chlorides, where Cm = C1-C4 for the bromides, and C1-C5 for the chlorides. These physicochemical properties were calculated from surface tension, conductivity, and fluorescence data. It was found that increasing the length of Cm (i.e., volume of the head group) leads to enhancement of surface activity, increase in the area per surfactant molecule at the water/air interface (Amin) and the degree of counter-ion dissociation (αmic). Our data also indicated that increasing the volume of the head group results in a decrease of the critical micelle concentration (cmc), Gibb's free energy of adsorption and micellization, and microscopic polarity of interfacial water. In order to delineate the effects of the presence of unsaturation in the HG, we included members that carry Cm = vinyl and allyl in the bromide series. The effect of these groups was found to be similar to removing a methylene group from Cm. The dependence of the solubilization of a lipophilic dye (Sudan IV) and a drug (nitrendipine) on the length of Cm was also studied.

Evaluation of Structurally Different Ionic Liquid-Based Surfactants in a Green Microwave-Assisted Extraction for the Flavonoids Profile Determination of Mangifera sp. and Passiflora sp. Leaves from Canary Islands.

Aqueous solutions of ionic liquids (ILs) with surface active properties were used as extraction solvents, taking advantage of their impressive solvation properties, in a green microwave-assisted solid-liquid extraction method (IL-MA-SLE) for the extraction of flavonoids from passion fruit and mango leaves. The extraction method was combined with high-performance liquid chromatography and photodiode-array detection (HPLC-PDA) and optimized by response surface methodology using the Box-Behnken experimental design. Under optimum conditions, the extraction efficiency of six structurally different IL-based surfactants was evaluated. Thus, imidazolium-, guanidinium- and pyridinium-type ILs with different tailorable characteristics, such as side chain length and multicationic core, were assessed. The decylguanidinium chloride ([C10Gu+][Cl–]) IL-based surfactant was selected as key material given its superior performance and its low cytotoxicity, for the determination of flavonoids of several samples of Passiflora sp. and Mangifera sp. leaves from the Canary Islands, and using as target analytes: rutin, quercetin and apigenin. The analysis of 50 mg of plant material only required 525 µL of the low cytotoxic IL-based surfactant solution at 930 mM, 10.5 min of microwave irradiation at 30 °C and 50 W, which involves a simpler, faster, more efficient and greener method in comparison with other strategies reported in the literature for obtaining bioactive compounds profiles from plants.

Sustainable Micro-Scale Extraction of Bioactive Phenolic Compounds from Vitis vinifera Leaves with Ionic Liquid-Based Surfactants.

This paper proposes a new sustainable and simple strategy for the micro-scale extraction of phenolic compounds from grapevine leaves with analytical purpose. The method is based on a microwave-assisted solid-liquid extraction approach (MA-SLE), using an aqueous solution of an ionic liquid (IL)-based surfactant as extraction phase. The method does not require organic solvents, nor any clean-up step, apart from filtration prior to the injection in the analytical system. Two IL-based surfactants were evaluated, and the method was optimized by using experimental designs, resulting in the use of small amounts of sample (100 mg) and extraction phase (2.25 mL), low concentrations of the selected 1-hexadecyl-3-butyl imidazolium bromide IL (0.1 mM), and 30 min of extraction time. The proposed methodology was applied for the determination of the polyphenolic pattern of six different varieties of Vitis vinifera leaves from the Canary Islands, using high-performance liquid chromatography and photodiode array detection for the quantification of the compounds. The proposed MA-SLE approach was greener, simpler, and more effective than other methods, while the results from the analysis of the leaves samples demonstrate that these by-products can be exploited as a source of natural compounds for many applications.

Compatibilization Effect of Ionic Liquid-Based Surfactants on Physicochemical Properties of PBS/Rice Starch Blends: An Initial Study.

Polybutylene succinate (PBS)/rice starch (RS) blends were prepared via the hot-melt extrusion technique through the usage of a twin-screw extruder without and containing ionic liquid-based surfactants (ILbS). Two types of ILbS were used, specifically, 1-dodecyl-3-methylimidazolium trifluoromethanesulfonate, [C12mim][OTf] and 1-dodecyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [C12mim][NTf2] were mixed into the PBS/RS blends at the different contents (0–8 wt.%). The tensile and flexural results showed that the blends containing ILbS have a high tensile extension and tensile energy compared to the blend without ILbS. The blends containing ILbS also have a high flexural extension compared with the blend without ILbS. The blends containing [C12mim][NTf2] have a significant improvement in the tensile energy (up to 239%) and flexural extension (up to 17%) in comparison with the blends containing [C12mim][OTf]. The FTIR spectra demonstrated that the presence of ILbS in the blends generated the intermolecular interactions (ion-dipole force and hydrophobic-hydrophobic interaction) between PBS and RS. The DSC results exhibited that the melting points of the prepared blends are decreased with the addition of ILbS. However, the TGA results showed that the thermal decomposition of the blends containing ILbS are higher than the blend without ILbS. The values of decomposition temperature were 387.4 °C, 381.8 °C, and 378.6 °C of PBS/RS-[C12mim][NTf2], PBS/RS-[C12mim][OTf], and PBS/RS, respectively. In conclusion, the ILbS could significantly improve the physicochemical properties of the PBS/RS blends by acting as a compatibilizer.

Relative permeability measurement in carbonate rocks, the effects of conventional surfactants vs. Ionic liquid-based surfactants

In the present study, the effect of two different kinds of surfactants namely conventional (Sodium dodecyl benzene sulfonate (SDBS)) and ionic liquid (IL)-based surfactants are investigated on the tertiary oil recovery using relative permeability concept. In this way, besides the Amott wettability index measurement, unsteady state core flooding tests are performed to not only find the effect of surfactant injection on tertiary oil recovery, but also to investigate their effects on relative permeability of carbonate rocks. In addition, for more reliable conclusions regarding the possible mechanisms, interfacial tension (IFT), compatibility and emulsification tests are carried out as a function of concentration. According to the results obtained through the core flooding experiments, it can be concluded that the injection of SDBS which substantially reduces the IFT value leads to higher tertiary oil recovery (26% based on original oil in place (OOIP)) although the ILs revealed more compatibility at the presence of harsh salinity conditions at any examined IL concentration in this study. Finally, the results obtained by plotting the relative permeability data and mining into the cross points one can conclude that in the case of using ILs, the active mechanisms during the tertiary oil recovery is dominantly related to wettability alteration mechanism while in the case of SDBS, the IFT reduction is the active mechanism.

Imidazolium-based ionic liquid surfactants as pseudostationary in combination with a chiral selector in micellar electrokinetic chromatography.

In recent years, ionic liquid-based surfactants have drawn more and more attention. As a new promising brand of surfactants, ionic liquid-based surfactants have their unique properties and superior aggregation behavior, which can be introduced as micellar pseudostationary in MEKC mode. In this paper, a novel ionic liquid-based surfactant, 1-butyl-3-methylimidazolum dodecyl sulfate [C4MIm][C12SO4], was synthesized through ion exchange reaction and applied for the first time to form micellar as pseudostationary phase for chiral separation with clindamycin phosphate as chiral selector. As observed, compared with conventional non-ionic liquid anionic surfactant, improved separation of tested drug enantiomers was obtained in the established MEKC system with ionic liquid-based surfactant. Parameters such as concentration of ionic liquid-based surfactants, type and proportion of organic modifier, concentration of chiral selector, and pH of buffer solution were systematically investigated to optimize the ionic liquid-based surfactant MEKC system. Graphical abstract.

Salt‐Induced Microstructural Transitions in Aqueous Dispersions of Ionic‐Liquids‐Based Surfactants

AbstractApplicability and performance ability of the surfactants are controlled through their aggregation behavior, which are modulated by employing external additives. In order to achieve favorable shape and sized nano‐aggregates, we have investigated the role of structure making hydrotop; sodium salicylate (NaSal) on the micellar transition of the functionalized and non‐functionalized ionic liquid based surfactants (ILBSs) (1‐hexadecyl‐3‐vinylimidazolium bromide and 1‐hexadecyl‐3‐methylimidazolium bromide) in aqueous medium. The micelle to vesicle transitions in the studied systems is explored using viscosity, dynamic light scattering and transmission electron microscopy measurements. For the first time we report the nano and micro‐structural aggregates of the vinylfunctionalized ILBSs with respect to the composition, and concentration of the additives; alkyl chain length and head group of ILBSs. Transmissions electron microscopy (TEM) revealed the formation of vesicles at high concentration of NaSal (∼1000 mM) for the vinylfunctionalized ILBS.

Synergistic Interaction between Cholesterol and Functionalized Ionic Liquid Based Surfactant Leading to the Morphological Transition

AbstractStable vesicular aggregate is the primary requisite to transport and deliver the biological and pharmaceutical standards. The serendipitous discovery of nonlipid vesicles made with the nonlipid building blocks, such as ionic liquid based surfactants (ILBSs) proved to be advantageous over others. In a quest to achieve stable, more rigid and hydrophobic vesicles from ILBSs, here we have investigated the lipid (cholesterol) induced unilamellar vesicle formation in the aqueous functionalized and nonfunctionalized ILBSs. The vesicles show outstanding stability with time, temperature and dilution with water. Spectroscopic (turbidity, steady state absorbance and fluorescence), scattering (dynamic light scattering) and microscopic (transmission electron microscopy) techniques were used to characterize the vesicles. The hydration behavior and rigidity associated with the vesicular bilayer on transforming from micellar assembly was characterized through steady state absorbance and fluorescence techniques. The unilamellar vesicles derived are compared with the conventional surfactant, i. e. cetyltrimethyl ammonium bromide.

Guanidinium ionic liquid-based surfactants as low cytotoxic extractants: Analytical performance in an in-situ dispersive liquid–liquid microextraction method for determining personal care products

The IL-based surfactant octylguanidinium chloride (C8Gu-Cl) was designed and synthetized with the purpose of obtaining a less harmful surfactant: containing guanidinium as core cation and a relatively short alkyl chain. Its interfacial and aggregation behavior was evaluated through conductivity and fluorescence measurements, presenting a critical micelle concentration value of 42.5 and 44.6mmolL−1, respectively. Cytotoxicity studies were carried out with C8Gu-Cl and other IL-based and conventional surfactants, specifically the analogue 1-octyl-3-methylimidazolium chloride (C8MIm-Cl), and other imidazolium- (C16MIm-Br) and pyridinium- (C16Py-Cl) based surfactants, together with the conventional cationic CTAB and the conventional anionic SDS. From these studies, C8Gu-Cl was the only one to achieve the classification of low cytotoxicity. An in situ dispersive liquid–liquid microextraction (DLLME) method based on transforming the water-soluble C8Gu-Cl IL-based surfactant into a water-insoluble IL microdroplet via a simple metathesis reaction was then selected as the extraction/preconcentration method for a group of 6 personal care products (PCPs) present in cosmetic samples. The method was carried out in combination with high-performance liquid chromatography (HPLC) and diode array detection (DAD). The method was properly optimized, requiring the use of only 30μL of C8Gu-Cl for 10mL of aqueous sample with a NaCl content of 8% (w/v) to adjust the ionic strength and pH value of 5. The metathesis reaction required the addition of the anion exchange reagent (bis[(trifluoromethyl)sulfonyl]imide − 1:1 molar ratio), followed by vortex and centrifugation, and dilution of the final microdroplet up to 60μL with acetonitrile before the injection in the HPLC-DAD system. The optimum in situ DLLME-HPLC-DAD method takes ∼10min for the extraction step and ∼22min for the chromatographic separation, with analytical features of low detection limits: down to 0.4μgL−1; high reproducibility: with RSD values lower than 10% (intra-day) and 16% (inter-day) for a spiked level of 15μgL−1; and an average enrichment factor of 89. The requirement of low volumes (30μL) of a low cytotoxic IL-based surfactant allows the method to be considered less harmful than other common analytical microextraction approaches.

Drug induced micelle-to-vesicle transition in aqueous solutions of cationic surfactants

Solubilization of the drug diclofenac sodium (DS) in micellar aggregates of ionic liquid-based surfactants and cetyltrimethylammonium bromide at 25 °C induces changes to worm-like micelles and vesicles, with potential use in drug delivery.

Impact of organic solvents on the micellization and interfacial behavior of ionic liquid based surfactants

To elucidate the role of organic solvents, in altering the micellization and interfacial behavior of Ionic Liquid based Surfactants (ILBSs), we had investigated the effect of formamide (FA), glycerol (GLY), ethylene glycol (EG) and 1-propanol (PRO) on the micellization and interfacial behavior of 1-tetradecyl-3-methylimidazolium bromide (C14mimBr) and 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) ILs, in aqueous solution by conductometric and tensiometric techniques at 298.15K. The micellization behavior has been determined by studying the changes in critical micelle concentration (cmc), degree of counter ion binding (β), gibbs free energy of micellization (ΔGm0) and interfacial behavior by studying various surface parameters. Micellization behavior was mainly studied in light of altering the relative permittivity of the medium and displacement of water layer, which disfavors the micellization and as a result increases cmc. Effect of solvophobic parameter (Sp) and packing parameter (P) on the micellization was also examined. Results have been compared with the conventional cationic surfactants with identical alkyl chain.

Tailored ionic liquid-based surfactants for the formation of microemulsions with water and a hydrophobic ionic liquid.

Microemulsions (μe) with water and a hydrophobic ionic liquid (IL) usually require 45-60 wt% surfactant to solubilize equal amounts of water and IL. To increase the efficiency we designed a new class of surfactants by combining a hydrophilic but IL-ophobic carbohydrate-based part with a hydrophobic but IL-ophilic IL-based part. These surfactants allow formulating microemulsions with 20 wt% surfactant only which opens up a new arena for efficient water-IL μes.

Ionic liquids versus ionic liquid-based surfactants in dispersive liquid–liquid microextraction for determining copper in water by flame atomic absorption spectrometry

ABSTRACTThis work compares the performance of dispersive liquid–liquid method (DLLME) as a prior step for determining copper by flame atomic absorption spectrometry (FAAS), when using the ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate (C4MIm-PF6) or the IL-based surfactant 1-hexadecyl-3-butylimidazolium bromide (C16C4Im-Br) as extractant solvents. For the water-insoluble C4MIm-PF6, the most conventional DLLME mode using acetonitrile as dispersive solvent was employed. For the water-soluble C16C4Im-Br, the in situ DLLME mode with lithium bis[(trifluoromethane)sulfonyl]imide (Li-NTf2) as metathesis reagent was employed. In both approaches, some effective parameters such as volumes of extractant and dispersive solvents, concentration of complexing agent, pH of sample solution, salting-out effect and final diluting solvent to ensure compatibility with FAAS, were properly optimised. The optimum conditions for the IL-DLLME method using C4MIm-PF6 were: 100 μL of neat C4MIm-PF6, 1 mL of acetonitrile, 10 mL of water, no control of pH for environmental waters, NaCl content of 23 g L−1, diethyl dithiocarbamate (DDTC) as complexing agent at 10 mg L−1 and final dilution of the micro-droplet with acetonitrile up to 70 µL. The optimum conditions for the in situ IL-DLLME method using C16C4Im-Br were: 0.8 mL of acetonitrile, 10 mL of water containing C16C4Im-Br at 25.2 mmol L−1, final dilution step of the micro-droplet with 200 µL of acetonitrile and remaining conditions as those of C4MIm-PF6. The analytical performance of both methods was similar, being slightly better for the IL-DLLME method using C4MIm-PF6, with limits of detection (LOD) of 3.3 µg L−1 (versus 5.1 µg L−1 when using C16C4Im-Br), precision values as intraday relative standard deviation (RSD in %) lower than 8.8% (being of 10% for the C16C4Im-Br method) and an enrichment factor of 54 (being 27 when using C16C4Im-Br). The DLLME-FAAS method with C4MIm-PF6 was used in the analysis of environmental waters with successful performance, with relative recoveries of 110% and 105%, and interday precision with RSD values of 21% and 7.4% for spiked levels of 60 and 160 µg L−1, respectively. The results obtained when analysing an urban wastewater sample coming from an inter-laboratory exercise was comparable to those obtained for other 93 laboratories. The method was also valid for the determination of Cu2+ in presence of foreign ions commonly found in natural waters.

Interfacial and aggregation behavior of dicationic and tricationic ionic liquid-based surfactants in aqueous solution

The interfacial and aggregation behavior of three dicationic and two tricationic ionic liquid-based (IL) surfactants in aqueous solutions have been carried out. The studied dicationic IL-based surfactants were 1,12-di(3-butylimidazolium)dodecane bromide ((C4Im)2C12-2Br), 1,12-di(3-decylimidazolium)dodecane bromide ((C10Im)2C12-2Br), and 1,12-di(3-hexadecylimidazolium)dodecane bromide ((C16Im)2C12-2Br). Two classes of trigonal tricationic surfactants containing triethylamine (Am) and 1,3,5-trimethylbenzene (Bn) cores were synthesized for first time and characterized, specifically, 3,3′,3″-octyl-1,1′,1″-(2-ethylamino) imidazolium bromide ((C8Im)3Am-3Br), and 3,3′,3″-octyl-1,1′,1″-(1,3,5)tris(methylene) benzene imidazolium bromide ((C8Im)3Bn-3Br). The critical micelle concentration (CMC) values and other aggregation parameters, including adsorption efficiency (pC20), surface tension at the CMC (γcmc), degree of dissociation (α), and the degree of counterion binding in the micelle (β) were obtained using a variety of techniques including surface tension, conductivity, and fluorescence measurements. For the first time, the aggregation numbers (Nagg) were also obtained for this group of surfactants. A study into the influence of acetonitrile on the stability and aggregation behavior of dicationic and tricationic IL-based surfactants was also undertaken. The CMC values of the dicationic surfactants clearly decrease as a function of the side chain, when the same linker is maintained. The CMC values of the tricationic surfactants were lower than analogous linear trimeric surfactants. For the novel tricationic surfactants, the effect of sodium salts (C6H5COONa, NaBr, and NaI) on the surface activity was also investigated. It was also observed that the surface activity parameters (pC20 and CMC/C20) of tricationic surfactants increased significantly in the presence of added electrolytes.