Cationic Surface Active Ionic Liquids Research Articles

Interfacial and micellar synergistic interactions between a phosphonium surface active ionic liquid and TX-100 nonionic surfactant: Surface tension and 1H NMR investigations

The adsorption and self-aggregation behaviors of a mixed system made of a cationic surface active ionic liquid (SAIL), dodecyltriphenylphosphnium bromide (C12TPB), and a nonionic surfactant, polyoxyethylene p-tertoctylphenyl ether (TX-100), were investigated in aqueous solution using tensiometry and 1H NMR measurements. From the surface tension data, relevant physico-chemical parameters were determined for different proportions of the components: critical micelle concentration (cmc), surface saturation adsorption, minimum surface area per surfactant molecule and surface tension at the cmc. The obtained data were treated through different theoretical models, namely those of Clint, Rubingh, Maeda and Rosen, which allow the determination of key thermodynamic properties. The results revealed, in both the mixed micelles and surface monolayer, the existence of a non-ideal behavior due to rather strong attractive links, confirmed by the 1H NMR data analysis. They are attributed mainly, besides the hydrophobic interaction, to firstly the ion–dipole interaction and the complex formation between the polyoxyethylene head of TX-100 and the quaternary phosphonium group of C12TPB, and secondly to an intermolecular π-π stacking and a hydrogen-bonds formation between the protons in α position of the phosphonium and the oxygen atoms of polyoxyethylene units of TX-100, giving rise to a strong synergism.

A formulation based on a cationic surface-active ionic liquid and an anionic surfactant for enhanced oil recovery at a carbonate reservoir

With the still huge dependence on crude oil, it is crucial to develop enhanced oil recovery techniques to improve reservoir production and lifespan. Carbonate reservoirs constitute over half the world's oil reserves, but they are challenging in terms of recovery due to their complex pore network, oil-wet or mixed-wet rocks, and harsh conditions of temperature and salinity. This work offers a significant contribution to the exploitation of these reservoirs. A new formulation, able to provide very low interfacial tension at high temperatures with reduced adsorption on carbonate rocks, was designed. A low-cost traditional alkyl benzene sulfonate (RECOLAS158) was mixed with the cationic surface active ionic liquid N,N-diethoxylated-N-tallow-N-ethylammonium ethylsulfate. A formulation containing 56.4 wt% RECOLAS158 was selected for its good performance in terms of phase behavior, injectability and interfacial tension at a wide range of temperatures and salinities. A very significant tertiary oil recovery (19.53% of the original oil in place) and low blend adsorption (0.086 mgblend/grock), demonstrated the promising performance of the formulation. The key mechanism associated to the improvement of oil recovery is interfacial tension reduction.

Ti3C2-MXene ionogel with long-term stability and high sensitivity for wearable piezoresistive sensors

Wearable piezoresistive sensors have attracted tremendous attention recently, which can be applied for health monitoring and human-computer interaction. MXenes, possessing high metallic conductivity and large specific surface area, are often used as the conductive filler in hydrogels and organohydrogels for piezoresistive sensors. However, the environmental instability of MXene composites caused by the easy oxidation of MXene is a long-standing issue which needs to be solved urgently. Herein, taking advantage of phase transfer achieved by cationic surface active ionic liquid 1-vinyl-3-dodecylimidazolium bromide ([VC12Im]Br), we combine Ti3C2Tx with hydrophobic ionic liquid to fabricate Ti3C2-MXene ionogel successfully, which exhibits high compressibility (2.97 MPa), high conductivity (0.908 mS/cm) and long-term stability (40 days). And the wearable piezoresistive sensor based on Ti3C2-MXene ionogel shows rapid response time (100 ms), high sensitivity (6.47 kPa−1) and wide detection range, thus can be used to monitor the tiny movements of human body parts, recognize vocalizations and handwriting. This preparation method develops a new path to fabricate Ti3C2-MXene ionogel with long-term stability and high sensitivity for wearable electronic devices.

PERFORMANCE EVALUATION OF 1-HEXADECYL-3- METHYLIMIDAZOLIUM BROMIDE, LAURYL GLUCOSIDE AND DECANE IN CREATING WINSOR TYPE-III MICROEMULSION

While ionic liquids are usually high in cost, only small amounts are needed to establish their beneficial characteristics combined with the utilization of a cosurfactant. A cationic surface-active ionic liquid, 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) has been chosen as the main surfactant because it is non-volatile, nonflammable, and able to withstand high temperature. However, it has been studied that this ionic liquid poses a major threat to the aquatic environment, thus another surfactant is needed as a cosurfactant. Lauryl glucoside was used as the cosurfactant because it is environmentally friendly, has low toxicity and excellent biodegradability. The potential of this surfactant mixture for enhanced oil recovery (EOR) application was investigated by conducting stages of phase behaviour study, specifically using the phase diagram method. The optimized formulation C16mimBr-lauryl glucoside microemulsion consists of 4 wt% salinity, 0.5 wt% C16mimBr, and 1 wt% lauryl glucoside were determined based on the appearance of a high volume of middle phase microemulsion in a wide range of oleic phase. The performance of the microemulsion system in reducing IFT was measured using a spinning drop tensiometer at room temperature. The presence of lauryl glucoside as a cosurfactant shows a decent performance in reducing IFT, thus showing the great potential of this biosurfactant, replacing traditional alcohol. It is concluded that the formulation of C16mimBr-lauryl glucoside microemulsion with optimized parameters reaches low IFT instead of ultralow. The critical micelle concentration was determined to be at 0.05 wt% of the aqueous phase.Keywords: enhanced oil recovery, surfactant, Ionic liquid, alkyl polyglucoside

Comparison of the interaction between propranolol hydrochloride (PPL) with anionic surfactant and cationic surface active ionic liquid in micellar phase

In this study, the interaction in binary mixtures comprising an amphiphilic drug (propranolol hydrochloride, PPL) and ionic surfactants (N-lauryl sarcosine sodium, NLS and 1-dodecyl-3-methylimidazolium bromide, SAIL) was investigated in micellar phase using conductometric technique in aqueous solution at 298.15 K. SAIL is a cationic surface-active ionic liquid with a specific critical micelle concentration(CMC). To identify the influence of polar head groups in interaction between components, the surfactants with the same alkyl chain length (C12) but with oppositely charged head groups were selected (NLS: anionic and SAIL: cationic). The deviation of experimental critical micelle concentration (CMCexp) from the corresponding ideal values of CMC (CMCid), the micellar compositions (X1 and X2), the mutual interaction parameter (βm), activity coefficients of the components in the mixed micelle (f1 and f2) and thermodynamic parameters have been calculated using different proposed theoretical models like Clint, Rubingh, and Motomura. The interaction parameter (βm) is negative values at all compositions for two systems (with two levels of values), showing attractive interactions between components. In comparison between the NLS/PPL and SAIL/PPL systems, the NLS/PPL system shows stronger micelle formation capability, smaller CMC values and stronger synergistic effect. The determined values of the micellar mole fraction of surfactant (X1) obtained from theoretical models signify the considerable contribution of surfactant in surfactant(1)/PPL(2) mixed micellization. Further, conductometry measurements indicate that the extent of counterion binding (α) of mixed micelles for SAIL/PPL system are higher than those found for NLS /PPL system.

Adsorption of Surface Active Ionic Liquids on Different Rock Types under High Salinity Conditions

A new class of surface active ionic liquids (SAIL) have been reported to be a greener alternative to the conventional surfactants in enhanced oil recovery (EOR). These SAILs work efficiently under harsh salinity conditions encountered in the reservoir thereby recovering more additional oil during the tertiary oil recovery process. Adsorption mechanism of SAILs on different rock surface is however, not yet reported in the literature. This article highlights adsorption mechanism of three cationic SAILs having different headgroups, viz., imidazolium, pyridinium, pyrrolidinium, on different rock surfaces (crushed natural carbonate rock and crushed sandstone rock). All the SAILs studied here however had the same tail length and same anion (Br−) attached to it. XRD and XPS characterization techniques reveal that the crushed natural carbonate rock contains a substantial amount of silica, thus rendering it a slight negative charge. Static adsorption tests show that the retention efficiency on the natural carbonate type of rock for all the SAILs was lower than the conventional cationic surfactant, CTAB. The adsorption data obtained thereby was examined using four different adsorption isotherm models (Langmuir, Freundlich, Redlich-Peterson, and Sips). Results suggest that Sips adsorption isotherm model can satisfactorily estimate the adsorption of all the surface active agents on the natural carbonate rock. Factors like mineralogical composition of rock surface, presence of divalents, temperature, and structure of surfactants strongly affect the amount of surfactant adsorbed on reservoir rock. In order to evaluate the simultaneous effect all these factors as well as their interdependence on the retention capability of the three SAILs, a design of experiments approach has been employed further in this study. Statistical analysis of the data obtained after performing the full factorial experiments reveal that at high salinity, imidazoluim based SAIL show minimal adsorption on crushed natural carbonate rock at higher temperature. In general, at a given ionic strength, with increasing temperature as the amount of divalent in the aqueous solution increases, the amount of SAIL adsorbed on both the rock types decreases. Electrostatic attraction is the basic mechanism in governing adsorption of SAILs on the two types of rock surfaces. Results presented in this work can be used for EOR schemes.

Modification of fatty acid vesicle using an imidazolium-based surface active ionic liquid: a detailed study on its modified properties using spectroscopy and microscopy techniques $$^{\S }$$ §

Fatty acid vesicles have attracted views as model protocell membranes in understanding the emergence of life, but their properties can be further modified in the presence of some external molecules. In this work, we have investigated the spontaneous formation of large unilamellar vesicles (LUVs) of oleic acid in aqueous medium in presence of a popular imidazolium-based cationic surface active ionic liquid (SAIL) $$[\hbox {C}_{16}\hbox {mim}]\hbox {Cl}$$ and studied the micelle–vesicle transition of aqueous $$[\hbox {C}_{16}\hbox {mim}]\hbox {Cl}$$ solution in presence of different molar fractions (f) of oleic acid. This newly formed oleic $$\hbox {acid}/[\hbox {C}_{16}\hbox {mim}]\hbox {Cl}$$ vesicles exhibit some modified properties compared to the pure fatty acid vesicles. Unlike pure fatty acid vesicles, these vesicles are stable in the pH range of 2 to 11.2. We have observed the fusion process of these oleic acid/SAIL vesicles to form giant unilamellar vesicles (GUVs) in presence of low concentration of NaCl solution. To investigate the dynamics of different oleic $$\hbox {acid}/[\hbox {C}_{16}\hbox {mim}]\hbox {Cl}$$ self-assemblies, we have used fluorescence correlation spectroscopy (FCS). The translational diffusion behavior of three different dyes, Rhodamine 6G, DCM and Pyrromethene 597, which are non-covalently bound to the different regions of the oleic acid/SAIL self-assemblies, have been determined using FCS during the micelle–vesicle transition and upon varying the pH of the vesicular solution. Oleic acid vesicles prepared in presence of a surface active ionic liquid $$[\hbox {C}_{16}\hbox {mim}]\hbox {Cl}$$ have been characterized. Modified properties of these vesicles like stability towards a greater pH range as compared to pure oleic acid vesicles and fusion of vesicles in presence of low concentration of NaCl solution have been studied.

Effect of a copolymer poly(4-styrenesufonic acid-co-maleic acid) sodium salt on aggregation behaviour of imidazolium based surface active ionic liquid in aqueous solution

Aim of the present investigation is to broaden an understanding of the interactions between imidazolium based cationic surface active ionic liquid (SAIL) 1-dodecyl-3-methylimidazolium bromide [C12mim][Br] and an anionic polyelectrolyte poly(4-styrenesufonic acid-co-maleic acid) sodium salt (PSSA-co-MA) in aqueous media by using fluorimetry, conductometry and tensiometry techniques. The various states of interaction and critical micelle concentration (cmc) have been reviewed due to the strong hydrophobic and electrostatic interactions. Also degree of ionization, α, cmc and various thermodynamic parameters were determined by conductivity measurement in the temperature range 298.15–318.15K. The surface tension curve displays the presence of pronounced knap in the surface tension at SAIL concentrations below cmc of the SAIL. The various surface parameters are calculated from surface tension measurement. Aggregation number (Nagg) and cmc were determined by fluorimetric measurements at temperature 298K. In all cases it was observed that the cmc values were decreased with increase in the concentration of polyelectrolyte this is attributed to the strong electrostatic interactions between SAIL and polyelectrolyte. Also the aggregation behaviour of SAIL begins shifting from entropy-driven to enthalpy-driven with increasing the concentration of polyelectrolyte and increase in temperature. The results obtained from different measurements are in good agreement with each other.

Concentration-Driven Fascinating Vesicle-Fibril Transition Employing Merocyanine 540 and 1-Octyl-3-methylimidazolium Chloride.

In this article, anionic lipophilic dye merocyanine 540(MC540) and cationic surface-active ionic liquid (SAIL) 1-octyl-3-methylimidazolium chloride (C8mimCl) are employed to construct highly ordered fibrillar and vesicular aggregates exploiting an ionic self-assembly (ISA) strategy. It is noteworthy that the concentration of the counterions has exquisite control over the morphology, in which lowering the concentration of both the building blocks in a stoichiometric ratio of 1:1 provides a vesicle to fibril transition. Here, we have reported the concentration-controlled fibril-vesicle transition utilizing the emerging fluorescence lifetime imaging microscopy (FLIM) technique. Furthermore, we have detected this morphological transformation by means of other microscopic techniques such as field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and cryogenic-transmission electron microscopy (cryo-TEM) to gain additional support. Besides, multiwavelength FLIM (MW-FLIM) and atomic force microscopy (AFM) techniques assist us in knowing the microheterogeneity and the height profile of the vesicles, respectively. We have replaced the SAIL, C8mimCl, by an analogous traditional surfactant, n-octyltrimethylammonium bromide (OTAB), and it provides a discernible change in morphology similar to that of C8mimCl, whereas 1-octanol is unable to exhibit any structural aggregation and thus reveals the importance of electrostatic interaction in supramolecular aggregate formation. However, the SAILs having the same imidazolium headgroup with different chain lengths other than C8mimCl are unable to display any structural transition and determine the importance of the correct chain length for efficient packing of the counterions to form a specific self-assembly. Therefore, this study reveals the synergistic interplay of electrostatic, hydrophobic, and π-π stacking interactions to construct the self-assembly and their concentration-dependent morphological transition.

Spectroscopic Studies on the Interaction of Dye and Surface Active Ionic Liquid

The interaction of both cationic dye Safranine T (ST) and anionic dye Congo red (CR) with anionic and cationic surface active ionic liquid 1-butyl-3-methyl imidazolium octyl sulphate ([BMIM] [OS]) and 1-decyl-3-methyl imidazolium chloride ([DMIM] [Cl]) has been investigated by absorbance and emission spectroscopy, time resolved fluorescence study and anisotropy method at premicellar and post micellar region. The interaction of dye with both the ionic liquids occurred electrostatically as well as hydrophobically. In case of ST, initially absorbance decreases up to a certain concentration without any shift of λmax, and then it increases with red shift of λmax. Absorption spectra of CR gave red shifted wavelength with addition of [BMIM] [OS], but at higher concentration of surface active ionic liquid [SAIL], no shifting was observed. Again, blue shifted λmax was found in lower range of [DMIM] [Cl]; but at higher concentration, it was further red shifted. Emission intensity increases in both dye-SAIL systems;...

Effect of anionic polyelectrolyte sodium carboxymethylcellulose on the aggregation behavior of surface active ionic liquids in aqueous solution

In the present study, we reported the effect of sodium carboxymethylcellulose (NaCMC), an anionic polyelectrolyte on the aggregation morphological variations of cationic surface active ionic liquids (SAILs) for example 1-tetradecyl-3-methylimidazolium bromide [C14mim][Br] and 1-hexadecyl-3-methylimidazolium bromide [C16mim][Br]. The measurements have been carried out by utilizing techniques such as surface tension, conductance, fluorescence, dynamic light scattering and rheology. The results obtained from surface tension measurements shows that surface properties and aggregation process of SAILs have been extensively influenced by the addition of polyelectrolyte. So, the humps have been observed in the tensiogram corresponding to different states of interaction. The various surface parameters such as surface excess concentration (Γmax), surface pressure at the interface (Πcmc), minimum area occupied by single SAIL molecule at air-solvent interface (Amin), adsorption efficiency (pC20) and surface tension at critical micelle concentration (cmc) (γcmc) have been calculated from surface tension measurements. The results obtained from tensiometric and conductometric measurements have been further confirmed by fluorescence, dynamic light scattering and rheology results. It has been observed that the cmc values of both the SAIL systems increases with increasing concentration of NaCMC.

Ionic liquids for low-tension oil recovery processes: Phase behavior tests

Chemical flooding with surfactants for reducing oil-brine interfacial tensions (IFTs) to mobilize residual oil trapped by capillary forces has a great potential for Enhanced Oil Recovery (EOR). Surface-active ionic liquids (SAILs) constitute a class of surfactants that has recently been proposed for this application. For the first time, SAILs or their blends with an anionic surfactant are studied by determining equilibrium phase behavior for systems of about unit water-oil ratio at various temperatures. The test fluids were model alkane and aromatic oils, NaCl brine, and synthetic hard seawater (SW). Patterns of microemulsions observed are those of classical phase behavior (Winsor I-III-II transition) known to correlate with low IFTs. The two anionic room-temperature SAILs tested were made from common anionic surfactants by substituting imidazolium or phosphonium cations for sodium. These two anionic and two cationic SAILs were found to have little potential for EOR when tested individually. Thus, also tested were blends of an anionic internal olefin sulfonate (IOS) surfactant with one of the anionic SAILs and both cationic SAILs. Most promising for EOR was the anionic/cationic surfactant blend of IOS with [C12mim]Br in SW. A low equilibrium IFT of ∼2·10−3mN/m was measured between n-octane and an aqueous solution having the optimal blend ratio for this system at 25°C.

Influence of trehalose on the interaction of curcumin with surface active ionic liquid micelle and its vesicular aggregate composed of a non-ionic surfactant sorbitan stearate

The present investigation unravels the effect of trehalose on 1-hexadecyl-3-methylimidazolium chloride ([C16mim]Cl), a cationic surface active ionic liquid (SAIL) micelle and SAIL ([C16mim]Cl)-nonionic surfactant (Sorbitan Stearate, Span 60) based vesicles. The influence of trehalose on size and morphology of the aggregates has been investigated using dynamic light scattering (DLS) and transmission electron microscopic (TEM) measurements. Besides, we have studied the dynamic properties of curcumin inside these aggregates using fluorescence spectroscopic based techniques. The results revealed that trehalose molecules play crucial role in modulation of the photophysical properties of curcumin in these organized assemblies.

Probing the Interaction between a DNA Nucleotide (Adenosine-5'-Monophosphate Disodium) and Surface Active Ionic Liquids by Rotational Relaxation Measurement and Fluorescence Correlation Spectroscopy.

This article demonstrates the interaction of a deoxyribonucleic acid (DNA) nucleotide, adenosine-5'-monophosphate disodium (AMP) with a cationic surface active ionic liquid (SAIL) 1-dodecyl-3-methylimidazoium chloride (C12mimCl), and an anionic SAIL, 1-butyl-3-methylimidazolium n-octylsulfate ([C4mim][C8SO4]). Dynamic light scattering (DLS) measurements and 1H NMR (nuclear magnetic resonance) studies indicate that substantial interaction is taking place among the DNA nucleotide (AMP) and the SAILs. Moreover, cryogenic transmission electron microscopy (cryo-TEM) suggests that SAILs containing micellar assemblies are transformed into larger micellar assemblies in the presence of DNA nucleotides. Additionally, the rotational motion of two oppositely charged molecules, rhodamine 6G perchlorate (R6G) and fluorescein sodium salt (Fl-Na), have been monitored in these aggregates. The rotational motion of R6G and Fl-Na differs significantly between SAILs micelles and SAILs-AMP containing larger micellar aggregates. The effect of negatively charged DNA nucleotide (AMP) addition into the cationic and anionic SAILs is more prominent for the cationic charged molecule R6G than that of anionic probe Fl-Na due to the favorable electrostatic interaction between the AMP and cationic R6G. Moreover, the influence of the anionic DNA nucleotide on the cationic and anionic SAIL micelles is monitored through the variation of the lateral diffusion motion of oppositely charged probe molecules (R6G and Fl-Na) inside these aggregates. This variation in diffusion coefficient values also suggests that the interaction pattern of these oppositely charged probes are different within the SAILs-nucleotide containing aggregates. Therefore, both rotational and translational diffusion measurements confirm that the DNA nucleotide (AMP) renders more rigid microenvironment within the micellar solution of SAILs.

Influence of head group on the interactional behavior of cationic surface active ionic liquids with pluronic F108 in aqueous medium

The present work aims at studying the interactions between surface active ionic liquids (SAILs) 1-dodecyl-3-methylimidazolium bromide [C12mim][Br]; N-dodecyl-N-methylpiperidinium bromide, [C12mpip][Br]; N-dodecyl-N-methylpyrrolidinium bromide, [C12mpyr][Br] and pluronic F108 in aqueous medium and to draw the comparison between the effect of different SAILs with respect to head group present in them. The binding of SAILs with pluronic F108 below as well as above the critical micelle temperature (cmt) of the pluronic has been studied by isothermal titration calorimetry (ITC), dynamic light scattering (DLS) and zeta (ζ) potential measurements. A combined analysis of these techniques revealed that SAILs can bind to monomeric as well micellar pluronic F108 with [C12mim][Br] showing a higher binding affinity in comparison to the other SAILs. Further, the interactions between SAILs and pluronic F108 in mixed micelles have been studied employing surface tension and fluorescence measurements, Various micellar, interfacial and thermodynamic parameters have being obtained for mixed systems of SAILs with pluronic F108. The interactions between F108-SAIL binary mixtures have been found to be non-ideal and strongly synergistic. The modifications in the physicochemical properties of pluronic F108 upon addition of SAILs are expected to enhance and expand the industrial and pharmaceutical applications of pluronics.

Spontaneous Formation of Multiarchitecture Vesicles of [C8mim]Br + [Na]DBS in Aqueous Medium: Synergic Interplay of Electrostatic, Hydrophobic, and π-π Stacking Interactions.

A mixture of a cationic surface active ionic liquid, [C8mim]Br and anionic surfactant, [Na]DBS has been shown to form unilamellar vesicles in water over an exceptionally wide mole fraction range of [C8mim]Br (x1 = 0.2 to 0.8). Formation of vesicles has been evidenced from transmission electron microscopy (TEM), cryo-TEM and atomic force microscopy (AFM) imaging. Cryo-TEM imaging of an equimolar mixture showed multiarchitectural unilamellar vesicles (spherical, tubular, and ribbon). Such complex architectures were earlier reported for Janus dendrimers of different structures (Science, 2010, 328, 1014). The synergism between oppositely charged single chain surfactants to form bilayer structures has been explained based on the evidence of π-π stacking interaction from 2D NOESY measurements, Coulombic interactions from zeta potential measurements and magnitude of interaction parameter from the critical aggregation concentration. The aggregation concentrations were measured from tensiometry and fluorescence using pyrene as a polarity probe. The phase behavior at different mixture compositions has been revealed from turbidity measurements and visual inspection. Hydrodynamic radii of self-assembled structures in the bulk solution phase were measured from dynamic light scattering. Vesicles formed have been explored as delivery vehicles for proteins using bovine serum albumin (BSA) as model.

Interfacial and aggregation behavior of aqueous mixtures of imidazolium based surface active ionic liquids and anionic surfactant sodium dodecylbenzenesulfonate

Abstract The present work aims to study the interactions of cationic surface active ionic liquids (SAILs), 1-alkyl-3-methylimidazolium chloride, ([C n mim][Cl], where n = 8, 10 and 12) with anionic surfactant, sodium dodecylbenzenesulfonate (SDBS) in aqueous medium employing various state of art techniques such as tensiometry, steady-state fluorescence, dynamic light scattering (DLS) and small angle neutron scattering (SANS). Tensiometric and steady-state fluorescence measurements have revealed the presence of strong synergistic interactions prevailing between the oppositely charged SDBS and SAILs. Using DLS and SANS techniques, the self organization behavior of SDBS-SAIL mixtures at different mixing ratios has been investigated. The results confirmed the presence of micelles/vesicles or micelles and vesicles together at different mixing ratios of the components. Further, the aqueous mixed systems have been utilized as structure orienting templates for the preparation of Ag nanoparticles via reduction of AgNO 3 employing sodium borohydride. The prepared nanoparticles have been characterized by Scanning electron microscopy (SEM), DLS and UV–vis spectroscopic techniques where the composition of the mixed micelles has been found to affect the morphology of formed Ag nanoparticles, remarkably.

Study the effect of substituent position in aromatic counterion to self-aggregation of cationic surface active ionic liquid in aqueous medium

Specific effects of m- and p-hydroxybenzoate anions (m-HB and p-HB) as counterion on the aggregation process of surface active ionic liquids based on 1-dodecyl-3-methylimidazolium were investigated by surface tension, conductivity and steady state fluorescence measurements. Compared to that for 1-dodecyl-3-methylimidazolium bromide (C12mimBr), lower critical micelle concentration (cmc) and larger Πcmc and pC20 values for these SAILs indicate that the introduction of aromatous counterions favors micellization and reduction of surface tension. The most incorporated salicylate anion can effectively screen electrostatic repulsion, promoting a closer arrangement of C12mimSal at air–solution interface. Thus m- and p-C12mimHB have smaller Γmax and larger Amin values than C12mimSal. From the results of conductivity measurements, the cmc values of these SAILs increase slightly with increasing temperature, which has similar trend with cationic SAIL, 1-alkyl-3-methylimidazolium bromide, [Cnmim]Br. The negative ΔGmθ values, mainly result from more negative-T ΔSmθ, reveal that the micellization process is spontaneous and entropy-driven in the whole studied temperature range. The data also show that ΔHmθ values of all systems are negative, which implies that the micellization process is exothermic. This work suggests that small changes, such as position of the substitute on aromatic ring of counterion, can considerably influence the micellization behavior of SAILs.

Interactions of new 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) based surface active ionic liquids with amitriptyline hydrochloride: Micellization and interfacial studies

A new series of cationic surface active ionic liquids (SAILs) based on DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) was synthesized through the quaternization of DBU by alkyl bromides. The SAILs viz. DBU-C12 (8-N-dodecyl-1,8-diazabicyclo[5.4.0]undec-7-en-8-ium bromide), DBU-C14 (8-N-tetradecyl-1,8-diazabicyclo[5.4.0]undec-7-en-8-ium bromide) and DBU-C16 (8-N-hexadecyl-1,8-diazabicyclo[5.4.0]undec-7-en-8-ium bromide) were obtained and their aggregation behaviour was examined by surface tension and conductivity measurements. The SAILs investigated displayed better surface activity than the imidazolium based SAILs (CnmimBr) as well as the conventional cationic surfactants, alkyltrimethylammonium bromides (CnTAB). They also showed a decrease in critical micelle concentration (cmc) values with an increase in the alkyl chain length. Further, their interactions with amphiphilic drug, amitriptyline hydrochloride (AMT) have also been studied by employing the theoretical models proposed by Rubingh, Motomura and Gibbs. The micellar interaction parameter (βm) is negative for most of the mole fractions of AMT (αAMT) in DBU-C14/DBU-C16+AMT systems, indicating attractive interactions. The interfacial parameters such as surface tension reduction efficiency (pC20), effectiveness of surface tension reduction (πcmc), maximum surface excess concentration at the air-water interface (Γmax) and minimum area per surfactant molecule (Amin) were also evaluated for the mixed systems of DBU based SAILs with AMT. The standard Gibbs free energy of micellization (ΔG°m) and the standard free energy of adsorption at the air/water interface (ΔG°ad) for these systems were found to be negative, confirming the feasibility of these drug–SAIL interactions.

Interaction of Bovine Serum Albumin with Ester-Functionalized Anionic Surface-Active Ionic Liquids in Aqueous Solution: A Detailed Physicochemical and Conformational Study

Ester-functionalized anionic surface-active ionic liquids (SAILs), 3-methyl-1-(ethoxycarbonylmethyl)imidazolium dodecylsulfate ([C(1)COOC(2)C(1)im][C(12)SO(4)]) and 3-methyl-1-(ethoxycarbonylmethyl)pyrrolidinium dodecylsulfate ([C(1)COOC(2)C(1)Py][C(12)SO(4)]), were synthesized. The tensiometric profiles demonstrate that, in pure water, the studied SAILs exhibit higher surface activity than the traditional anionic surfactant, sodium dodecyl sulfate (SDS), and cationic SAILs, 1-dodecyl-3-methylimidazolium bromide ([C(12)mim]Br) and N-dodecyl-N-methylpyrrolidimium bromide (C(12)MPB), with the same hydrocarbon chain length. The interaction between bovine serum albumin (BSA) and the anionic SAILs in pH 7.4 buffer solution was systematically investigated by various techniques. The results show that the cationic ring has a slight effect on the BSA-SAIL interaction. The binding isotherms of BSA with the SAILs display four characteristic regions with increasing SAIL concentration. The unfolding of BSA occurs in the third region. Fluorescence spectroscopy indicates that the studied SAILs cause the exposure of tryptophan residues to a hydrophobic environment, and [C(1)COOC(2)C(1)im][C(12)SO(4)] can more effectively reduce the fluorescence intensity of BSA at low SAIL concentrations than [C(1)COOC(2)C(1)Py][C(12)SO(4)]. Circular dichroism spectroscopy evidences that the denaturation extent of BSA induced by [C(1)COOC(2)C(1)im][C(12)SO(4)] is higher than that of [C(1)COOC(2)C(1)Py][C(12)SO(4)].