Anionic Surface Active Ionic Liquid Research Articles

Self-assembly of choline-based surface-active ionic liquids and concentration-dependent enhancement in the enzymatic activity of cellulase in aqueous medium.

The micellization of choline-based anionic surface-active ionic liquids (SAILs) having lauroyl sarcosinate [Sar]-, dodecylsulfate [DS]-, and deoxycholate [Doc]- as counter-ions was investigated in an aqueous medium. Density functional theory (DFT) was employed to investigate the net interactional energy (Enet), extent of non-covalent interactions, and band gap of the choline-based SAILs. The critical micelle concentration (cmc) along with various parameters related to the surface adsorption, counter-ion binding (β), and polarity of the cores of the micelles were deduced employing surface tension measurements, conductometric titrations and fluorescence spectroscopy, respectively. A dynamic light scattering (DLS) system equipped with zeta-potential measurement set-up and small-angle neutron scattering (SANS) were used to predict the size, zeta-potential, and morphology, respectively, of the formed micelles. Thermodynamic parameters such as standard Gibb's free energy and standard enthalpy change of micellization were calculated using isothermal titration calorimetry (ITC). Upon comparing with sodium salt analogues, it was established that the micellization was predominantly governed by the extent of hydration of [Cho]+, the head groups of the respective anions, and the degree of counter-ion binding (β). Considering the concentration dependence of the enzyme-SAIL interactions, aqueous solutions of the synthesized SAILs at two different concentrations (below and above the cmc) were utilized as the medium for testing the enzymatic activity of cellulase. The activity of cellulase was found to be ∼7- to ∼13-fold higher compared to that observed in buffers in monomeric solutions of the SAILs and followed the order: [Cho][Sar] > [Cho][DS] > [Cho][Doc]. In the micellar solution, a ∼4- to 5-fold increase in enzymatic activity was observed.

Phase diagrams and formulation mechanism of microemulsions with hydroxyl group functional anionic surface active ionic liquids

One functional hydroxyl group-containing anionic surface active ionic liquids (SAILs), 1-(3-hydroxypropyl)-3-methylimidazolium dodecyl sulfate ([MPmim][DS]) and 1-(3-hydroxypropyl)-3-butylimidazolium dodecyl sulfate ([MPbim][DS]) were synthesized and characterized with 1HNMR, 13CNMR, FT-IR spectroscopy, thermogravimetric analysis (TGA), and elemental analysis. The critical micellar concentration (CMC) values of [MPmim][DS] and [MPbim][DS] were obtained through measurements of surface tension and electrical conductivity. The capability of [MPmim][DS] and [MPbim][DS] to form microemulsions was assessed. The influence of the hydroxyl group of imidazolium cation on microemulsion formulation was elucidated using Density functional theory (DFT) simulations. Critical micellar concentration (CMC) values for [MPbim][DS] and [MPmim][DS] are 0.51 mmol/L and 0.99 mmol/L, respectively. The micellization processes of [MPbim][DS] and [MPmim][DS] are spontaneous, endothermic, and entropy-driven. [MPmim][DS] or [MPbim][DS] as surfactant, ethyl laurate microemulsions are formulated. The single-phase region area (SME) percent of ethyl laurate microemulsions are 60% and 66%. The single-phase region area percent of different microemulsions follows the trend: [MPbim][DS] > [MPmim][DS]. Introducing the functional hydroxyl group into the imidazolium cation significantly expands the SME area of microemulsions. DFT simulations are employed to analyze hydrogen bonding and electronic energy interactions among cations, DS anion, [MPmim][DS], [MPbim][DS], and ethyl laurate. Two types of hydrogen bonds are formed in [MPmim][DS] or [MPbim][DS], as C-H…O, and O-H…O. In [MPmim][DS], the hydroxyl group of imidazolium cation participates in the formation of a strong hydrogen bond with DS anion, exemplified by strong hydrogen bond O18-H19…O64 (1.972 Å). These advancements offer critical insights into the design of surface active ionic liquids, enhancing their functional properties and broadening the potential for innovative microemulsion applications in various industries.

Impact of Inulin on Self-Assembled Behavior of Anionic Surface Active Ionic Liquids: Conductometric, Spectroscopic and Antimicrobial Studies

The self-assembled behavior of greener anionic surface-active ionic liquids (SAILs), namely Tetrapropylammonium Dodecylsulfate (TPADS) and Tetrabutylammonium Dodecylsulfate (TBADS), in an aqueous solution of biocompatible saccharide inulin, has been extensively investigated using conductometric and fluorescence probe techniques at different temperatures. The critical micellar concentration (CMC) values have been determined by observing the breakage point in κ vs. [SAIL] plots. These values as obtained from fluorescence probe techniques have also been calculated. It has been found that the CMC values obtained through both conventional and spectroscopic techniques exhibited close agreement. Additionally, thermodynamic parameters of micellization, such as Gibbs free energy (ΔGmo), enthalpy (ΔHmo), and entropy (ΔSmo) were calculated using conductivity data as they play a crucial role in understanding the various interactions prevailing in the SAIL-inulin-water system. It was found that the micellization process for SAILs in the aqueous inulin solution occurs readily, as indicated by the Gibbs free energy of micellization. Furthermore, the antimicrobial properties of biocompatible SAILs in 0.2% w/w aqueous inulin solution were explored against bacterial strains, gram-positive i.e. B. cereus, S. aureus, and gram-negative namely P. aeruginosa. Molecular docking studies were also conducted to determine the binding energy and binding sites between TBADS and the proteins of the aforementioned bacteria. These investigations help to enhance the understanding of potential applications and interactions of SAILs in the presence of inulin.

Mixed Micellization of Promazine Hydrochloride with Cholinium‐Based Anionic Surface Active Ionic Liquids and their Potential Application for the Synthesis of Silver Nanoparticles

AbstractThis work is aimed to study the interaction of an amphiphilic drug, promazine hydrochloride (PMZ) and two anionic surface active ionic liquids (SAILs), cholinium laurylsarcosinate [Cho][Sar] and cholinium deoxycholate [Cho][Doc] using conductivity, UV‐visible spectroscopy and fluorescence techniques. The results obtained by all three techniques indicated non‐ideal behavior and synergistic interactions between the PMZ drug and SAIL mixed systems. Further, the drug‐SAIL mixtures were used to stabilize silver nanoparticles (Ag NPs) in aqueous solution. The results of UV‐visible spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM) showed that PMZ and SAILs had strong electrostatic and hydrophobic interactions which played a significant role in the stabilization of Ag NPs. The morphological analysis of the Ag NPs showed the formation of various types of aggregates controlled by the internal packing of PMZ‐[Cho][Sar]/[Cho][Doc] mixed systems. These drug‐SAIL based NPs could be used in separation and synthesis applications in nanotechnology by altering the structure of drugs and SAILs.

A density functional theory study on the water aggregation behaviour of fatty acid-based anionic surface active ionic liquids

The hydrogen bond interactions between methyl-imidazolium cation (MIM+) and fatty acid anions (CmHnCOO–, where m = 1–6; n-3–13) of ionic liquids are studied in both gas phase and water phase using density functional theory. The structural properties show that the presence of N–H···O and C–H···O hydrogen bonds between [MIM]+ and [CmHnCOO]– (m = 1–6; n-3–13) ionic liquids. From the vibrational frequency analysis, it was found that the hydrogen bond interaction between [MIM]+ and [CmHnCOO]– (m = 1–6; n-3–13) ionic liquids are red-shifted in frequency. The natural bond orbital analysis show that the N–H···O hydrogen bond associated with the large charge transfer which has the higher stabilization energy (i.e. E(2) ~ 38 kcal/mol). Further, the cation/anion–water cluster (H2O)1–3 interactions show that the water molecules are preferred to interact with anions. In the case of ionic liquid–water cluster interaction, the water molecules occupies the interstitial space between cation and anion of ionic liquids which results in weakening the cation–anion interaction.

Experimental and DFT studies on micellization features of anionic surface active ionic liquid and nonionic surfactant mixtures: Effect of imidazolium cations

The micellization characteristics of nonionic surfactant (Triton TX-100, p-octyl polyethylene glycol phenyl ether) and two anionic surface active ionic liquids (SAILs) were investigated by surface tension measurements, steady state fluorescence tests, dynamic light scattering (DLS), HNuclear magnetic resonance, and density functional theory (DFT) calculations. The anionic SAILs were 1-ethoxycarbonyl-3-methylimidazolium dodecyl sulfate ([Etmim][C12H25SO4]) and 1-ethoxycarbonyl-3-butylimidazolium dodecyl sulfate ([Etbim][C12H25SO4]). CMCmix values of SAIL/TX-100 mixtures were between CMC values of individual surfactants, and decreased with the increase of the molar fraction of TX-100. The negative β values (interaction parameter) of SAIL/TX-100 mixtures indicated good synergistic effect amid SAIL/TX-100 mixtures. [Etbim][C12H25SO4] showed stronger attractive interactions than [Etmim][C12H25SO4] during SAIL/TX-100 micellization. The mixed micelles contained a larger molar fraction of TX-100 over the entire range of composition. At same molar fraction of TX-100, X1 values of [Etbim][C12H25SO4]/TX-100 mixtures were lower than those of [Etmim][C12H25SO4]/TX-100 mixtures. With addition of SAIL, the particle sizes of SAIL/TX-100 micelles decreased. With the increase of SAIL concentrations, the particle sizes of SAIL/TX-100 micelles decreased. In presence of SAILs ([Etmim][C12H25SO4] or [Etbim][C12H25SO4]), all protons of TX-100 moved downfield. The chemical shifts of protons in [Etmim][C12H25SO4] or [Etbim][C12H25SO4] slightly moved upfield. DFT simulations demonstrated the presence of hydrogen bonds between the imidazolium cation of SAILs and EO chain of TX-100, and between sulfate anion group(-SO4-) of SAILs and hydrogen atoms in TX-100. The information will shed light on the rapid screening of novel anionic SAIL/surfactant mixtures for practical applications.

Experimental and DFT studies on foam performances of lauryl ether sulfate-based anionic surface active ionic liquids

Three lauryl ether sulfate-based anionic surface active ionic liquids (SAILs), 1-butyl-3-methylimidazolium lauryl ether sulfate ([Bmim][C12H25O(C2H4O)2SO3]), 1-hexyl-3-methylimidazolium lauryl ether sulfate ([Hmim][C12H25O(C2H4O)2SO3]), and 1-octyl-3-methylimidazolium lauryl ether sulfate ([Omim][C12H25O(C2H4O)2SO3]) were synthesized. Physicochemical properties (surface properties, micellization, adsorption, and aggregation parameters) of three anionic SAILs and sodium lauryl ether sulfate (SLES) were determined. The critical micelle concentration (CMC) values of [Bmim][C12H25O(C2H4O)2SO3], [Hmim][C12H25O(C2H4O)2SO3], and [Hmim][C12H25O(C2H4O)2SO3] (from surface tension) were 0.569 mmol/L, 0.361 mmol/L, and 0.190 mmol/L, respectively. Micellization of three SAILs were spontaneous, endothermic, and entropy-driven. Foaming performances (foaming ability, foam stability, and foam composite index) of three anionic SAILs and SLES were determined using Ross-Miles methods. The foaming abilities of three SAILs followed: [Hmim][C12H25O(C2H4O)2SO3] > [Bmim][C12H25O(C2H4O)2SO3] > [Omim][C12H25O(C2H4O)2SO3]. While the foam stabilities and foam composite index (FCI) of three SAILs followed: [Omim][C12H25O(C2H4O)2SO3] > [Hmim][C12H25O(C2H4O)2SO3] > [Bmim][C12H25O(C2H4O)2SO3]. The structure effect of SAILs on foam performances were analyzed using density functional theory (DFT) calculations. Binding energy values of three SAIL hydrates followed the trend: [Omim][C12H25O(C2H4O)2SO3](H2O)n > [Hmim][C12H25O(C2H4O)2SO3](H2O)n > [Bmim][C12H25O(C2H4O)2SO3](H2O)n. DFT results showed the increase of alkyl chain length of imidazolium cation was beneficial for the stability of SAIL hydrates, which resulted in higher foam performances. The information will shed light on screening of novel SAILs for surfactant foam enhanced oil recovery (EOR).

Effect of alkyl chain length of imidazolium cations on foam properties of anionic surface active ionic liquids: Experimental and DFT studies

Two anionic surface active ionic liquids (SAILs), 1-hexyl-3-methylimidazolium dodecyl sulfate ([Hmim][C12H25SO4]) and 1-octyl-3-methylimidazolium dodecyl sulfate ([Omim][C12H25SO4]) were synthesized using imidazolium ionic liquids (ILs) and sodium dodecyl sulfate (SDS). The critical micelle concentration (CMC) values, thermodynamic properties, and aggregation parameters were determined using surface tension measurements, steady state fluorescence tests, and electrical conductivity measurements. CMC values (from surface tension) of [Hmim][C12H25SO4] and [Omim][C12H25SO4] were 1.075 mmol/L and 0.278 mmol/L, respectively. The micellization process of [Omim][C12H25SO4] and [Hmim][C12H25SO4] was spontaneous, endothermic, and entropy-driven. Foaming performances (foaming ability, foam stability, and foam composite index) of three SAILs ([Bmim][C12H25SO4], [Hmim][C12H25SO4], and [Omim][C12H25SO4]) were determined using Ross-Miles methods. The foaming abilities of SAILs followed the order: [Hmim][C12H25SO4] > [Bmim][C12H25SO4] > [Omim][C12H25SO4]. While the foam stabilities and foam composite index (FCI) of SAILs followed the order: [Omim][C12H25SO4] > [Hmim][C12H25SO4] > [Bmim][C12H25SO4]. The structure effect of three SAILs ([Bmim][C12H25SO4], [Hmim][C12H25SO4], and [Omim][C12H25SO4]) on foam performances were analyzed by density functional theory (DFT) calculations. Binding energy of three SAIL hydrates followed the trend: [Omim][C12H25SO4](H2O)n > [Hmim][C12H25SO4](H2O)n > [Bmim][C12H25SO4](H2O)n. DFT results showed the increase of alkyl chain length of imidazolium cation was beneficial to the stability of SAIL hydrates, which resulted in higher foam performances. The information will shed light on rapid screening of novel surface active ionic liquids for surfactant foam enhanced remediation (SFER).

PH Changes in the Micelle-Water Interface of Surface-Active Ionic Liquids Dictate the Stability of Encapsulated Curcumin: An Insight Through a Unique Interfacial Reaction between Arenediazonium Ions and t-Butyl Hydroquinone.

The chemical kinetic (CK) method, which involves the reduction of 4-hexadecylbenzenediazonium ions (16-ArN2+) by antioxidants (in the present case, TBHQ) occurring exclusively at the interface of the association colloids, was employed to establish the changes in the chemical reactivity of anionic surface-active ionic liquids (SAILs) as a function of the concentration and the composition in their mixed states. We used sodium dodecyl sulfate and different SAILs based on the dodecylsulfate surfactant containing 1-alkyl-3-methylimidazolium cations as counterions having a varying alkyl chain length of 4 (bmim), 8 (omim), and 12 (ddmim) carbon atoms. The structural transitions of aggregates of the SAILs from the micellar to vesicular form were observed as a function of concentration in single surfactant systems and as a function of composition in mixed surfactant systems. Results of the reduction kinetics of 16-ArN2+ at the interface of such aggregates, which depends on the acid/base equilibria at the interface, gave an insight into the changes in the interfacial H+ ions with the change in the hydrophobicity of the counterions of SAILs and the morphological changes from micelles to vesicles as a function of concentration or composition. These changes in the interfacial pH correlate very well with the stability of curcumin within these self-assemblies, which exclusively depends on the pH of the medium and highlights the importance of the results obtained from the CK method in selecting the appropriate medium/conditions for the stabilization of the bioactive molecules.

Temperature- and Composition-Induced Multiarchitectural Transitions in the Catanionic System of a Conventional Surfactant and a Surface-Active Ionic Liquid

The mixture of the cationic surfactant, cetyltrimethylammonium bromide (CTAB), and anionic surface-active ionic liquid, 1-butyl-3-methylimidazoliumdodecyl sulfate (bmimDS), has been studied as a function of the mole fraction of CTAB, XCTAB, with the total surfactant concentration fixed at 50 mM using turbidity measurements, rheology, dynamic light scattering, differential scanning calorimetry, small-angle neutron scattering, and small-angle X-ray scattering techniques. The catanionic mixture has been found to exhibit phase transitions from vesicles to micelles as a function of temperature, with some mole fractions of CTAB showing dual transitions. Solutions of XCTAB = 0.2 to 0.5 exhibited a single transition from vesicles to cylindrical micelles at 45 °C. With an increase in the mole fraction of CTAB from 0.55 to 0.65, dual structural transitions at 30 and 45 °C were observed. The microstructural transition at 30 °C is ascribed to the vesicle aggregation process with smaller vesicles fusing into bigger ones, whereas the transition at 45 °C was evaluated to be the vesicle-to-cylindrical micelle transition. However, at higher mole fractions of CTAB, XCTAB from 0.65 to 0.90, a single transition from vesicles to small cylindrical/spherical micelles was observed in the solutions, at a lower temperature of 30 °C. To the best of our knowledge, such a microstructural transitions as a function of temperature in a single mixture of cationic and anionic surfactants without any additive has not been reported so far.

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.

Experimental and DFT studies on surface properties of sulfonate-based surface active ionic liquids

Two anionic surface active ionic liquids (SAILs), 3-methyl-1-ethoxycarbonylimidazolium decanesulfonate ([Etmim][C10H21SO3]) and 3-methyl-1-ethoxycarbonylimidazolium dodecanesulfonate ([Etmim][C12H25SO3]) were synthesized and studied. The surface properties, aggregation properties and thermodynamic parameters of [Etmim][C10H21SO3] and [Etmim][C12H25SO3] aqueous solutions were determined using surface tension and electrical conductivity. Micelle formation of [Etmim][C10H21SO3] and [Etmim][C12H25SO3] was spontaneous and entropy-driven.Density functional theory (DFT) calculation was used to optimize the configuration of the anions (C10H21SO3, and C12H25SO3), imidazolium cation ([Etmim]+), and SAILs ([Etmim][C10H21SO3] or [Etmim][C12H25SO3]) with different number of water molecules (1–3) using Gaussian 16 at B3LYP/6-31G(d,p) level.Typical hydrogen bonds, bond length changes, bond angle changes, and charge changes of typical atoms in hydrated complexes were analyzed. For imidazolium cation hydrates, H2O formed two types of hydrogen bonds with cation ([Etmim]+). For sulfonate anion hydrates, H2O formed two types of hydrogen bonds with anions ([C10H21SO3]- or [C12H25SO3]-). Hydrogen atoms in H2O formed hydrogen bonds with oxygen atoms of polar sulfonate anions in three ways: 1:1, 2:1, and 2:1. The typical electron withdrawing atoms (N and O) in imidazolium cation was beneficial for the micelles formation. The electrostatic repulsion and electrostatic attractive interaction between polar groups of SAILs affected the CMC values of [Etmim][C10H21SO3] or [Etmim][C12H25SO3] aqueous solutions. Binding energy (D0), difference of binding energy (ΔD0) of sulfonate ion hydrates and SAIL hydrates confirmed the tendency of [Etmim][C12H25SO3] micelle formation was higher than that of [Etmim][C10H21SO3].

Effect of cation substituent of dodecanesulfate-based anionic surface active ionic liquids on micellization: Experimental and theoretical studies

Anionic surface active ionic liquid (SAIL), 1-butyl-3-ethoxycarbonylimidazolium dodecanesulfate ([Etbim][C12H25SO4]) was synthesized. The dependence of micellization of dodecanesulfate-based anionic SAILs on cation substituents of anionic SAILs was analyzed using experimental and theoretical studies. Critical micelle concentration of [Etbim][C12H25SO4] was 1.17 mmol/L at 298.15 K. [Etbim][C12H25SO4] showed superior surface property than [Bmim][C12H25SO4] with same dodecanesulfate anion.Theoretical density functional theory (DFT) calculation was used to determine the micellization tendency of anionic SAILs ([Bmim][C12H25SO4] and [Etbim][C12H25SO4]). CMC difference of [Etbim][C12H25SO4] and [Bmim][C12H25SO4] was ascribed to the electrostatic interaction (repulsion or attraction) and hydrophobic interaction of cations ([Bmim]+ and [Etbim]+), dodecanesulfate anion, anionic SAILs ([Bmim][C12H25SO4] or [Etbim][C12H25SO4]), and the interactions toward water molecules in aqueous solution. The hydrocarbon chain lengths of [Bmim]+ and [Etbim]+ reflected the different hydrophobic interaction of cations, which clarified that the important role of cation substituents on micellization of [Etbim][C12H25SO4] and [Bmim][C12H25SO4]. Atomic charge distribution of cations will play important role on the further hydration toward water molecules or electrostatic attraction toward [C12H25SO4]− anion. Typical hydrogen bonds and charge changes of typical atoms were beneficial for electrostatic attraction and electrostatic repulsion between polar groups of SAILs. The electrostatic repulsion and electrostatic attraction between polar groups of SAILs affected the CMC values of [Bmim][C12H25SO4] and [Etbim][C12H25SO4]. Changes of binding energy (D0) and difference of binding energy (ΔD0) confirmed the tendency of [Etbim][C12H25SO4] micelle formation was higher than that of [Bmim][C12H25SO4].

Refolding of acid denatured cytochrome c by anionic surface-active ionic liquid: Choice of anion plays key role in refolding of proteins

This study was performed to check the effect of temperature on the refolding of acid-denatured horse heart cytochrome c (h-cyt c) at pH 2.0 under the influence of anionic surface active ionic liquid (SAIL) 1-butyl-3-methylimidazolium octyl sulfate ([C4mim][C8OSO3]), various techniques were performed viz. UV–vis, steady-state fluorescence, time-resolved fluorescence, circular dichroism (CD), FT-IR and dynamic light scattering. We found SAIL, [C4mim][C8OSO3] upon addition to the h-cyt c in unfolded state at pH 2.0, stabilized the molten globule (MG), which acts as an intermediate during the protein folding pathway. The investigation of the refolding of h-cyt cin an unfolded state with [C4mim][C8OSO3] shows a surfactant like behavior and stabilizes the MG-like state with the help of electrostatic and hydrophobic interactions. The creation of an MG-like state reveals the presence of a regular structure formed in the presence of SAIL [C4mim][C8OSO3]. The thermodynamic parameters of the refolding of h-cyt c by [C4mim][C8OSO3] were also quantified at various temperatures (25 °C–40 °C). The m value calculated for refolded states of h-cyt c by [C4mim][C8OSO3] shows a noticeable difference. The lower values of m (at higher temperatures) suggest less efficient refolding. This shows the refolding ability of the [C4mim][C8OSO3] decreases with increasing the temperature. Moreover, the anionic SAILs were efficiently utilized in the protein renaturation studies and could be effectively used to solve problems of misfolding and aggregation of proteins.

Exploration on surface and bulk properties of anionic surface active ionic liquid 1-butyl-3-methylimidazolium dodecylbenzenesulfonate and non-ionic polymer polyvinylpyrollidone

Here, the complex formation among anionic surface active ionic liquid (SAIL) 1-butyl-3-methylimidazolium dodecylbenzenesulfonate [C4mim][DBS] and non-ionic polymer polyvinylpyrollidone (PVP) in aqueous solution has been studied. An attempt has been made to study the interactions in bulk and at interface via different techniques such as tensiometry, conductivity, dynamic light scattering (DLS) and nephelometric turbidity. From tensiometric measurements, some important surface parameters have been derived. From conductometric measurements, different thermodynamic parameters have been calculated and interpreted in terms of physicochemical interactions prevailing into the system. The aggregate formation has been tracked with DLS and nephelometric turbidity to understand the complexation dynamics.

Unveiling the interaction between carbon nanodot and IR light emitting fluorescent dyes inside the confined micellar environment

In this contribution, using microwave heating of polyethylene glycol (PEG 200), we have prepared carbon nanodot (CND). It is found that in aqueous medium as well as in the micellar solutions of triblock copolymer, P123 and in anionic surface active ionic liquid (SAIL), 1-butyl-3-methylimidazolium n-octylsulfate ([C4mim][C8SO4]) the fluorescence intensity of CND gets quenched in the presence of cationic cyanine dye HITCP and cationic phenoxazine dye Nile blue (NB). Stern-Volmer constant indicates that the quenching of fluorescence intensity is more in the aqueous medium compared to P123 and [C4mim][C8SO4] i.e., (BmimOs) micelles. Time-correlated single photon counting (TCSPC) measurement reveals that the fluorescence quenching is static in nature and the quenching through Förster resonance energy transfer (FRET) process is not dominant here. Addition of both the cationic dye molecules (HITCP and NB) in CND solution generates new excited state absorption peaks in transient absorption measurement. This observation suggests that a transient species is generated through photoinduced electron transfer (PET) between the donor-acceptor pairs and this PET is responsible for the fluorescence quenching of CNDs by the dye molecules. Moreover, this electron transfer kinetics is relatively faster in bulk water compared to that inside P123 and BmimOs micelle due to the intervention of the surfactant molecules between CND and the dye molecules. Therefore, this study provides a new insight about the PET dynamics between CND and fluorescent dye molecules.

Dodecyl sulfate-based anionic surface-active ionic liquids: synthesis, surface properties, and interaction with gelatin

Four dodecyl sulfate-based anionic surface-active ionic liquids were synthesized. Physicochemical parameters of surface-active ionic liquids (SAILs) or SAIL/gelatin aqueous solutions were demonstrated. Critical micelle concentration (cmc) values of [Emim][C12H25SO4], [Amim][C12H25SO4], [Bmim][C12H25SO4], and [Etmim][C12H25SO4] were 2.10 mmol/L, 1.95 mmol/L, 0.95 mmol/L, and 0.86 mmol/L at 298.15 K, respectively. cmc values of four SAILs followed the decreasing trend: [Emim][C12H25SO4] ≈ [Amim][C12H25SO4] > [Bmim][C12H25SO4] ≈ [Etmim][C12H25SO4]. The alkyl chain length (ethyl to butyl group) and electron absorption effect (carboxylate ester or allyl group) of substituent in cationic imidazolium groups played important role in micelle formation of SAILs. cmc values of SAIL/gelatin aqueous solutions were lower than those of SAILs. Micelle formation (SAIL or SAIL/gelatin) was spontaneous, exothermic, and entropy-driven. From DFT calculation, typical hydrogen bonds were found between active hydrogen atom of imidazole ring and oxygen, sulfur atoms of sulfate anion group. The information obtained would provide guide for design and synthesis of novel SAILs for wide gelatin application.

Systematic investigation of the effects of an anionic surface active ionic liquid on the interfacial tension of a water/crude oil system and its application to enhance crude oil recovery

A typical anionic surface active ionic liquid (SAIL), 1-butyl-3-methyl-imidazolium dioctylsulfosuccinate (BMOT), was introduced to chemical enhanced oil recovery. The ability of BMOT to reduce the interfacial tension (IFT) of water/crude oil was evaluated for its potential application in surfactant flooding. Compared with the traditional anionic surfactant AOT and another anionic SAIL 1-butyl-3-methylimidazolium dodecyl sulfate used in the control experiments, the effects of intramolecular electrostatic attraction and size match were employed to interpret the high interfacial activity of BMOT. The effects of salt and temperature on the water/crude oil IFT further verified the proposed mechanisms. Moreover, BMOT exhibited a satisfactory displacement performance to greatly improve the crude oil recovery (12.5% of the initial oil in place) in core flooding tests.

Micellization behavior of anionic surface active ionic liquid 1-butyl-3-methylimidazolium dodecylbenzenesulfonate in aqueous solutions of nonionic polymer polyethylene glycol: Insights into competing mechanisms

In this study, an understanding of interactions among the anionic surface active ionic liquid (SAIL) 1-butyl-3-methylimidazolium dodecylbenzenesulfonate [C4mim][DBS] and non-ionic low molecular weight polymer polyethylene glycol 400 (PEG 400) in aqueous solution has been developed systematically. Various techniques such as tensiometry, conductivity, dynamic light scattering (DLS), nephelometric turbidity and rheology have been employed to understand the exquisite interplay of different competing mechanisms prevailing between these unlike molecules in bulk as well as in the interfacial region. Surface activity of the current systems at air-aqueous interface have been evaluated using by deriving various important surface parameters, such as surface excess concentration (Гmax), surface pressure at interface (Πcmc), minimum area occupied by one molecule of SAIL at air-solvent interface (Αmin), adsorption efficiency (pC20) and surface tension at critical micelle concentration (cmc) (γcmc). Also, the thermodynamic parameters such as standard free energy of micellization (ΔGm°), standard enthalpy of micellization (ΔHm°) and standard entropy of micellization (ΔSm°) have been evaluated from conductivity measurements. The process of micellization has been found to be exothermic and spontaneous thermodynamically in presence of PEG supported by gain in entropy. The values of critical micelle concentration (cmc) decrease with increase in concentration of PEG which signals towards the predominance of ion-dipole interactions as well as hydrophobic interactions. However, at the higher concentration (0.045 g/L PEG), the cmc has been found to increase due to modification in surface and bulk structure of system. These results have been confirmed by the electrical conductivity measurements. The aggregate formation has also been tracked with the help of dynamic light scattering and nephelometric turbidimetry which provides useful information regarding the complexation dynamics. The rheological measurements have been carried out with the intent of understanding the complex behavior of these SAIL-polymer systems.

Investigation of physicochemical properties between poly(ethylene glycol)/poly(vinylpyrrolidone) and 1-butyl-3-methylimidazolium dodecyl sulfate in aqueous solution

In the present communication, the physicochemical properties between an anionic surface active ionic liquid (SAIL) 1-butyl-3-methylimidazolium dodecyl sulfate [C4mim][C12SO4] and nonionic polymers poly(vinylpyrrolidone) (PVP)/poly(ethylene glycol) (PEG) have been investigated by conductance and surface tension measurements. From these measurements the critical aggregation concentration (cac), critical micelle concentration (cmc), and degree of ionization (α) have been estimated. To understand the aggregation and interfacial behaviour of [C4mim][C12SO4] towards PVP and PEG, various thermodynamic and surface parameters have also been derived and discussed. The results exhibit that [C4mim][C12SO4] interacts strongly with PVP as compared to PEG.