Imidazolium-based Surface Active Ionic Liquids Research Articles

Analyzing the modulations induced in the mixed micellar behavior of 1-alkyl-3-butylimidazolium based surface-active ionic liquids with an antibiotic drug in aqueous media

Abstract The study aims to scrutinize the mixed micellization and interfacial behavior of two 1-alkyl-3-butylimidazolium based surface-active ionic liquids (SAILs) i.e., 1-decyl-3-butylimidazolium bromide [C10bim][Br] and 1-tetradecyl-3-butylimidazolium bromide [C14bim][Br] under the influence of streptomycin sulphate (SS) drug in 5 mM concentration in aqueous media. Imidazolium-based SAILs have unique physicochemical properties and greater surface activity than conventional surfactants, which allows them to increase drug permeability, making them better drug carriers than currently available formulations. To fully utilize [C14bim][Br] and [C10bim][Br] in drug delivery applications, deep insight into the interactions occurring in the mixed micellar [C10bim][Br]/[C14bim][Br] systems in the drug’s presence are necessary to be examined. Thus, the study is conducted using conductivity and surface tension measurement techniques to fully exploit the self-assembly, micellization behavior and interactions occurring in the pure and mixed micellar system of [C10bim][Br]/[C14bim][Br] in water and 5 mM of SS solution in aqueous media. For this, various thermodynamic, surface-active and mixed micellar parameters of micellization have been calculated and analyzed with respect to change in mole fraction, temperature and addition of SS in solution.

Investigation of aggregation behavior and surface properties of cationic surface-active ionic liquids and sodium carboxymethylcellulose mixed systems

Abstract The impact of different concentrations of sodium carboxymethyl cellulose (NaCMC) on the micellization process in cationic, ester-functionalized, ethyl-substituted imidazolium-based surface-active ionic liquids (SAILs) ([C n Eeim]Br where, n = 12, 14, 16) were investigated using specific conductivity and surface tension measurements at 298 K. The study focused on determining the critical micelle concentration (CMC) of the three pure SAILs and their mixtures with NaCMC to evaluate various thermodynamic and interfacial parameters. The results showed that the CMC values decreased significantly with increasing hydrophobicity of the SAILs, while the CMC increased with a gradual increase in the NaCMC mole fraction in the SAIL–NaCMC mixed systems. It was observed that the excess free energy of micellization ( ∆ G e x m ${{\increment}G}_{ex}^{m}$ ) and the minimum free energy of surface at equilibrium ( ∆ G min s ${{\increment}G}_{\mathrm{min}}^{s}$ ) exhibited an opposite behaviour, indicating that the formed mixed micelles were stable while the formed surface was unstable. The results of this study are useful for evaluating the properties of SAIL–NaCMC mixed systems to improve and better understand their applications in the food, medical and cosmetic industries.

Unraveling the Molecular Interactions of Imidazolium-Based Surface-Active Ionic Liquid [C15mim][Br] with Biologically Active Amino Acids Glycine, l-Alanine, l-Valine

Unraveling the Molecular Interactions of Imidazolium-Based Surface-Active Ionic Liquid [C15mim][Br] with Biologically Active Amino Acids Glycine, l-Alanine, l-Valine

Influence of urea/glucose on the mixed micellization behavior of amitriptyline hydrochloride and 1-hexadecyl-3-methylimidazolium chloride (ionic liquid) mixtures: An experimental and theoretical investigation

Mixtures of an antidepressant drug, amitriptyline hydrochloride (AMT), and ionic liquid, 1-hexadecyl-3-methylimidazolium chloride (HMICl), were investigated by tensiometry at a temperature of 298.15 K with diverse mole fraction (α1) of HMICl to determine the association, surface, and thermodynamic properties. Fourier transform infrared (FTIR) and UV–visible spectroscopy were also used to estimate the interactions between AMT and HMICl. AMT can treat depression, anxiety, and other mental illnesses. Imidazolium-based surface-active ionic liquids are ideal for biomedical uses because of their unique physicochemical properties. The interaction between AMT and HMICl was also examined using non-aqueous solvent systems (500 mmol·kg−1 urea and 250 mmol·kg−1 glucose). The ideal cmc (cmcid) measured for the mixed system (AMT + HMICl) tensiometry was notably smaller than the critical micelle concentration (cmc). As a result, AMT and HMICl interact fairly well, and interaction also increased when the α1 of HMICl increased. The cmc values for pure and mixed solutions in urea were higher than those in aqueous, while in glucose, they were lower. Hypothetical models, including those of Clint, Motomura, Rubingh, and Rosen, have been used to determine the association, interfacial, and thermodynamic properties. For each constituent, the activity coefficients were consistently < 1 for micellar along with interface, exhibiting the intermolecular interactions amongst constituents as well as nonideal behavior. The excess free energy was negative in each case, implying that mixed micelles and monolayers have higher stability than micelles and monolayers of single components. The direct interaction of AMT and HMICl was also characterized by FTIR and UV–visible analysis, similar to the tensiometric method. In summary, the ionic liquid HMICl may be an effective drug delivery vehicle.

Influence of an antibiotic drug neomycin sulphate on mixed micellization behavior of imidazolium based surface-active ionic liquids in aqueous media

Imidazolium-based surface-active ionic liquids (SAILs) have unique physicochemical features that make them ideal for biomedical applications. Because SAILs have a higher surface activity than conventional surfactants, they can improve drug permeability across biomembranes, making them superior drug carriers than existing solutions. In-depth studies of interactions prevailing in mixed micellar system of SAILs in the presence of drug are required to fully exploit the promise of these materials in drug delivery applications. Thus, various thermodynamic, mixed micellar and surface-active properties of two imidazolium-based SAILs with different cationic structures i.e.1-dodecyl-3-ethylimidazolium bromide [C12eim][Br] and 1-dodecyl-3-butylimidazolium bromide [C12bim][Br] have been determined in water and 5 mM neomycin sulphate solution in aqueous media. The study has been conducted for different mole fractions of mixed micellar system of SAILs using conductivity and surface tension measurement techniques. Various theoretical models such as Clint, Rubingh, Motomura and Rodenas models have been applied to understand the interactions prevailing in the mixed [C12eim][Br] /[C12bim][Br] system in water and neomycin sulphate solution in aqueous media.

Studies on thermodynamics of micellization of imidazolium-based surface-active ionic liquid [C15mim][Br] in aqueous media: Effect of D(+)-Xylose and D(+)-Glucose

Owing to the extensive applications of surfactant-based systems, it is of extreme importance to understand the influence of various external additives on the system properties of surfactant solutions. Ionic liquids with long alkyl chain are extensively researched for their properties as surfactants. Herein, the micellization properties of the IL, [C15mim][Br] in the absence and in the presence of different concentrations of D(+)-Xylose and D(+)-Glucose as external additives have been scrutinized using numerous techniques such as electrical conductivity, UV–Visible, Fluorescence and FT-IR measurements at (298.15, 303.15 and 308.15)K. The values of important physicochemical properties essentially, CMC, degree of counter-ion dissociation, and various thermodynamic parameters which have been computed from conductivity measurements. The CMC values obtained using UV–Vis and Fluorescence technique also validate the results from conductivity measurements. Analyses of CMC values indicate that the studied carbohydrates promote the micellization of IL in the order: D(+)-Glucose > D(+)-Xylose as a consequence of their solute-out effect.

Ionic liquid-based catanionic vesicles: A de novo system to judiciously improve the solubility, stability and antimicrobial activity of curcumin

Aqueous solubility and stability of curcumin could be ameliorated through its encapculation within the micellar and vesicular assemblies. This could protect curcumin from the attack of inactivating enzymes in the biological fluid and improve its medicinal and therapeutic effects. In our efforts to design surfactant based organized assemblies as drug carrier, herein, we had reported the formation of catanionic vesicles to encapsulate curcumin. The catanionic vesicles are formed through synergistic interaction between sodium butyrate (NaBut) and ester functionalized morpholinium and imidazolium-based surface active ionic liquids (SAILs). Fluorescence resonance energy transfer (FRET) and small-angle neutron scattering (SANS) were among the methods that were used to confirm the presence of curcumin within the bilayer of the vesicles. Loading capacity and stability of the curcumin within the micelles and vesicles were investigated. Results concludes that vesicles because of their higher hydrophobic character improve the encapsulation and inhibit the degradation of curcumin. The curcumin loaded catanionic vesicles were found effective against Gram-positive and Gram-negative bacteria and must be exploited for clinical applications. The newly fabricated system would pave the way for the stabilization of the curcumin and increased its application potential in the field of biotechnology and sustained drug delivery.

Alterations induced in the micellization behavior of dioctyl sodium sulfosuccinate in the presence of imidazolium-based surface-active ionic liquids in aqueous medium

The present work describes the effect of 1-nonyl-3-methylimidazolium bromide [C9mim][Br] and 1-dodecyl-3-methylimidazolium bromide [C12mim][Br] on aggregation behavior of anionic surfactant dioctyl sodium sulfosuccinate (NaAOT) in aqueous medium by employing different techniques such as conductivity measurement, UV–Visible spectroscopy and FT-IR spectroscopy. The conductivity data of anionic surfactant in the aqueous solution of surface-active ionic liquids is taken experimentally in the temperature range from 293.15 to 308.15 K with the interval of 5 K at various concentrations that is, (0.04, 0.08, 0.12, and 0.16) wt.% of both the SAILs. The critical micelle concentration (CMC) of NaAOT is detected to alter in the presence of both the SAILs. Temperature dependence of CMC obtained from conductivity measurements is utilized to evaluate various thermodynamic parameters of micellization such as, standard free energy of micellization (), standard enthalpy of micellization (), and standard entropy of micellization (). The UV–Visible spectroscopic study is utilized to confirm CMC values obtained from conductivity measurements, which are found to be in good agreement. FT-IR Spectra are recorded to analyze the structural changes that prevailed in both systems.

Microscopic insights on the structural and dynamical aspects of Imidazolium-based surface active ionic liquid micelles

Ionic liquids have drawn vast attention due to their extraordinary physicochemical properties and their relevance in a wide range of applications. As a result of their inherent amphiphilic nature, many ionic liquids are emerging as novel surfactants, being referred to as surface active ionic liquids (SAILs). Under suitable conditions in aqueous solution, these SAILs self-assemble to form nanostructures such as micelles and vesicles. Here, we report on the structure and dynamics of one such SAIL micellar system, 1-Decyl-3-methylimidazolium Bromide (DMIMBr), as studied using fully atomistic molecular dynamics (MD) simulation and quasi-elastic neutron scattering (QENS). Results are compared with a conventional surfactant, dodecyltrimethylammonium bromide (DTAB) micelles. MD simulations showed that while the structure of the DMIMBr micelle is very similar to that of DTAB, the conformational flexibility of the alkyl chains is starkly different. The alkyl chains in the SAIL are more ordered, having fewer gauche defects. This is consistent with experimental results obtained using QENS which also showed slower alkyl chain segmental dynamics. MD results also show restricted dynamics of the hydration water in DMIMBr micelles, of a sub-diffusive nature, suggesting stronger affinity of water molecules to the imidazolium moiety. Thus the decreased flexibility in the alkyl chains could arise from the slower hydration dynamics. In contrast, the lateral motion of the surfactant is found to be relatively faster in DMIMBr micelles than in DTAB micelles. The understanding gained from this study provides a microscopic insight about the dynamical aspects of SAIL micelles, which might be useful for related applications including micellar catalysis and nanoparticle synthesis.

The Role of Imidazolium-Based Surface-Active Ionic Liquid to Restrain the Excited-State Intramolecular H-Atom Transfer Dynamics of Medicinal Pigment Curcumin: A Theoretical and Experimental Approach.

The naturally occurring polyphenolic compound curcumin has shown various medicinal and therapeutic effects. However, there are various challenges associated with curcumin, which limits its biomedical applications, such as its high degradation rate and low aqueous solubility at neutral and alkaline pH. In the present study, efforts have been directed towards trying to resolve such issues by encapsulating curcumin inside the micelles formed by imidazolium-based surface-active ionic liquid (SAIL). The shape and size of the micelles formed by the SAIL have been characterized by using DLS analysis as well as TEM measurements. The photo-physics of curcumin in the presence of ionic liquid (IL) and also with the addition of salt (NaCl) has been explored by using different optical spectroscopic tools. The time-dependent absorption studies have shown that there is relatively higher suppression in the degradation rate of curcumin after encapsulation by the imidazolium-based SAIL in an aqueous medium. The TCSPC studies have revealed that there is deactivation in the nonradiative intramolecular hydrogen transfer process of curcumin in the presence of IL micelles as well as with the addition of salt. Furthermore, the time-dependent fluorescence anisotropy measurement has been carried out to figure out the location of curcumin inside the micellar system. In order to correlate all experimental findings, density functional theory (DFT) and classical molecular dynamics (MD) simulations at neutral pH media have been performed. It has been found that the van der Waals force of interactions plays a major role in the stabilization of curcumin in the micelles rather than the coulombic forces. It also has been observed that the van der Waals interactions remain unaffected in the presence of salt. However, as revealed by the MD simulation results, the micelles are found to be more compact in size after the addition of salt. The RMSD results show that the micelles formed by the SAIL achieve greater stability after a particular time constraint. Our results have divulged that the SAIL could act as a promising drug delivery system.

Electrochemical response and computational approach on surface-active ionic liquid (SAIL) in metal corrosion inhibition

This exploration highlights the protective corrosion inhibition properties of imidazolium-based surface-active ionic liquid (SAIL): 1-dodecyl-3-methylimidazolium bromide (C12MImBr) on mild steel (MS) in acidic environment (1 M HCl). A systematic electrochemical study was performed employing the potentiodynamic polarization technique for measuring corrosion current and corrosion rate via Tafel plot which is well complemented by weight loss method covering the range of pre-micellar, at critical micelle concentration (CMC), and post-micellar concentration of C12MImBr. Findings exhibited the inhibition efficiency enhancement of about ~ 96% with increase in [C12MImBr]. Electrochemical impedance spectroscopy (EIS) calculations showed an amendment in the impedance parameters (Rt and Cdl) with [C12MImBr] which indicated a successive adsorption of the material resulting into a shielding layer formation on the MS. Scanning electron microscopic study gave the supporting visual confirmations of the MS surface morphology which inferred that the MS surface counterattack the corrosion process more in presence of C12MimBr than in its absence. Thermodynamic study inferred the corrosion process to be spontaneous and that it obeyed Langmuir isotherm. Finally, the impact of the inhibitor structure on the corrosion inhibition efficacy to give a hypothetical interpretation about inhibitor performance was elucidated by computational simulation approach.

Transforming micelles into mixed micelles: a promising approach to tune the catalytic performance of imidazolium-based surface active ionic liquids toward degradation of rhodamine B.

Herein, we demonstrate that the catalytic performance of imidazolium-based surface-active ionic liquid (SAIL) micelles can be significantly enhanced through the addition of an appropriate type and amount of intelligently conceived amphiphile to form mixed micelles. Specifically, we show that the catalytic performance of 1-dodecyl-3-methyl imidazolium chloride (DDMIMCl) micelles toward the reductive degradation of rhodamine B (RhB), a carcinogenic dye extensively used in multiple industrial applications, can be appreciably boosted through addition of Brij56, a nonionic surfactant. Detailed kinetic investigations on the catalytic performance of pre- and post-micellar concentrations of DDMIMCl and its mixed micelles with Brij56 over various mole fractions, toward the reductive degradation of RhB, are presented. The data analyzed in light of Berezin's kinetic model suggest that the addition of Brij56 to DDMIMCl micelles significantly enhances their catalytic performance. The catalytic activity exhibited by the DDMIMCl-Brij56 (XBrij56 = 0.2) mixed micellar system is better than that reported for many state-of-the-art nanoparticle/homogenous catalysts. The results explained in light of Berezin's kinetic model are well supported by physico-chemical studies like conductometry, fluorimetry and dynamic light scattering. The presented results anticipate stimulation of extensive research activity for exploiting the mixed micellization approach as a novel avenue for modulating the catalytic performance of SAILs.

Synthesis, physicochemical characteristics and antimicrobial studies of ethyl-substituted imidazolium-based surface active ionic liquids (SAILs)

A series containing higher members of ethyl-substituted imidazolium-based surface active ionic liquids (SAILs) [Cneim]Br, (n = 12, 14, 16) has been synthesized by a two-step reaction pathway. They were characterized by FT-IR, 1H NMR and 13C NMR and their effect on self-aggregation behavior in aqueous solution has been examined, employing conductometric and tensiometric methods besides fluorescence measurements and UV-visible spectroscopy. The conductivity data were recorded at different temperatures and thermodynamic parameters of micelle formation such as, standard Gibbs free energy (∆Gmo), standard enthalpy (∆Hmo), standard entropy (∆Smo) were evaluated. The process of micellization is entropy driven and supported by Gibbs free energy measurements. Interfacial parameters have also been evaluated by employing surface tension technique. The SAILs were also analyzed for their antimicrobial activity by taking eleven kinds of bacterial strains.

As Catalytic as Silver Nanoparticles Anchored to Reduced Graphene Oxide: Fascinating Activity of Imidazolium Based Surface Active Ionic Liquid for Chemical Degradation of Rhodamine B

A kinetic study, first of its kind, regarding the catalytic activity of imidazolium-based surface-active ionic liquid (SAIL) viz. 1-dodecyl-3-methyl imidazolium chloride ([DDMIM][Cl]) toward the reductive degradation of a model cationic dye viz. rhodamine B (RhB) is presented. The catalytic activity of the pre and post micellar concentrations of SAIL [DDMIM][Cl], its conventional analogue surfactant dodecyltrimethylammonium bromide ([DTAB]) and silver (Ag) nano-particles anchored to the reduced graphene oxide (Ag-rGO) toward reductive degradation of RhB was explored. The catalytic activity observed for the [DDMIM][Cl] is much better than that of DTAB and is almost comparable to the activity exhibited by Ag-rGO. The catalytic rate constants (kcat) estimated in presence of pre-micellar concentrations of [DDMIM][Cl] (10 mM), DTAB (12 mM) and in presence of Ag-rGO as catalyst were found to be 11.48 × 10−2 min−1, 3.4 × 10−2 min−1 and 14.35 × 10−2 min−1 respectively. The results clearly establish the fascinating catalytic activity (almost comparable to that exhibited by Ag-rGO) of [DDMIM][Cl] for the reductive degradation of a widely used carcinogenic, mutagenic and toxic organic dye of great environmental concern. The presented results are expected to stimulate intense research activities that may uncover new opportunities toward exploitation of the catalytic activity of aqueous SAIL solutions. Surface active ionic liquid [DDMIM][Cl] is significantly more active than its conventional analogue DTAB and almost as active as Ag-rGO in facilitating the NaBH4 assisted chemical degradation of rhodamine B (RhB)-one of the most carcinogenic, mutagenic and toxic organic dyes.

Complexation Behavior of β-Lactoglobulin with Surface Active Ionic Liquids in Aqueous Solutions: An Experimental and Computational Approach.

The nature of functionalization of alkyl chains of imidazolium-based surface active ionic liquids (SAILs) with amide or ester moiety led to contrasting complexation behavior toward the globular protein, bovine serum albumin. This prompted us to further investigate the SAIL-dependent colloidal behavior of another globular protein, β-lactoglobulin (βLG), to probe the origin of varying structural transformations in globular proteins induced by SAILs. Herein, we investigated the colloidal systems of βLG, rich in β-sheet structure, in the presence of four structurally different SAILs using a multitechnique approach. The complexation behavior, both at the air-solution interface and in bulk, is supplemented by different techniques. Docking studies have complemented the obtained experimental results. The specificity of structure, H-bonding ability of SAILs, and inherent structure of protein are found to govern their complexation behavior in terms of size, shape, and polarity of protein-SAIL complexes along with varying degrees of structural alterations in globular proteins. The present work is expected to be very useful in establishing a deep understanding of the structure-property relationship between the nature of proteins and SAILs for their complexation and colloidal behavior for various biomedical applications.

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.

Thermodynamics of aggregation of imidazolium-based surface active ionic liquids in aqueous poly(ethylene oxide) media

The aggregation behaviour of two imidazolium-based surface active ionic liquids (SAILs), e.g., 1-decyl-3-methylimidazolium chloride (C10MeImCl) and 1-hexadecyl- 3-methylimidazolium chloride (C16MeImCl) in aqueous solutions was investigated in presence of varying amount of poly(ethylene oxide) (PEO) to explore the possible SAIL-PEO interactions. Electrical conductivity measurements were performed in aqueous solutions of PEO having two different molar mass over a selected temperature range. The critical micellization concentrations of the investigated SAILs in PEO-water media were always found to be higher than those in pure water. PEO was found to play a dual role in the SAIL-PEO-water ternaries. It has been concluded that the PEO molecules added to water modify the property of the medium besides binding a very small fraction of the surfactant ions prior to the commencement of the micellization of SAILs. The thermodynamic parameters of micellization such as Gibbs free energy (ΔGm0), standard enthalpy (ΔHm0), and standard entropy (ΔSm0) of aggregation were estimated from the temperature dependence of the critical micellization concentration values. The effects of concentrations of PEO, and molar mass of PEO on the self-aggregation of the C10MeImCl and C16MeImCl have been discussed in terms of the phenomena prevailing in these solutions. The observed enthalpy-entropy compensation effect in these SAIL-PEO-water ternaries provided important information as to the behaviour of the PEO-water media with respect to the ions present in solution.

Self-assembly of imidazolium-based surface active ionic liquids in aqueous solution: The role of different substituent group on aromatic counterions

Self-assembly behavior of 1-dodecyl-3-methylimidazolium o-anisate (C12mimA) and 1-dodecyl-3-methylimidazolium o-bromobenzoate (C12mimB) in aqueous solution was systematically explored, respectively. Combined with the concerning results of 1-dodecyl-3-methylimidazolium salicylate (C12mimSal) reported previously, impact of aromatic counterions with various substituent group on the aggregation behavior of surface active ionic liquids (SAILs) was demonstrated. Compared with C12mimSal, inferior surface activity of C12mimA and C12mimB can be attributed to deficiency of H-bonding. Lower critical micelle concentration (cmc) of C12mimB than C12mimA may result from the less negative interaction energy between it and water molecule, testified by density functional theory (DFT) calculations. An investigation of temperature effect on cmc reveals that, micellization processes of these two SAILs are entropic-driven within the range of temperature studied. Polarized optical microscopy (POM) and small angle X-ray scattering (SAXS) were employed to determine the generation of lyotropic liquid crystals (LLCs). Similar to C12mimSal, a hexagonal liquid crystalline phase (H1) and a cubic liquid crystalline phase (V2) appear successively with the increasing concentration of C12mimA and C12mimB. While only at higher concentration than C12mimSal, they can exhibit V2 phase. Structural parameters calculated from SAXS patterns suggest that higher concentration or temperature can lead to a closer alignment of SAIL molecules. Rheological results of LLC formed by the two SAILs show traits of general H1 phase analogous to C12mimSal. This work can provide insights into the self-assembly behavior of SAILs and facilitate their potential applications in some fields, e.g. nanomaterial preparation and drug delivery, etc.

Effect of Imidazolium-Based Surface-Active Ionic Liquids on the Orientation of Liquid Crystals at Various Fluid/Liquid Crystal Interfaces.

A series of imidazolium-based surface-active ionic liquids (IM-SAILs), viz., single-chained IM-SAILs, 1-alkyl-3-methylimidazolium bromide ([Cnmim]Br, n = 12, 14, 16), 1-dodecyl-3-methylimidazolium salicylate ([C12mim]Sal), 1-dodecyl-3-methylimidazolium 3-hydroxy-2-naphthoate ([C12mim]HNC), 1-dodecyl-3-methylimidazolium cinnamate ([C12mim]CA), 1-dodecyl-3-methylimidazolium para-hydroxy-cinnamate ([C12mim]PCA), gemini IM-SAIL, and 1,2-bis(3-dodecylimidazolium-1-yl)ethane bromide ([C12-2-C12im]Br2), along with three short-chained ionic liquids (ILs) [ethylammonium nitrate (EAN), propylammonium nitrate (PAN), and butylammonium nitrate (BAN)] were synthesized and applied to nematic liquid crystal (LC)/fluid interfaces. First, we evaluated the influence of the length and number of aliphatic chains as well as the counterion in the IM-SAIL structures on the anchoring of LCs at the aqueous/LC interface. It was observed that the threshold concentration of [Cnmim]Br (n = 12, 14, 16) decreased with the increase in aliphatic chain length. And double-chained [C12-2-C12im]Br2 has a far lower threshold concentration than single-chained [C12mim]Br. But the alteration of counterions (e.g., Br- and aromatic counterions) scarcely affected the anchoring of LCs at the interface. Second, we investigated the alignment of LCs at the diverse IL/LC interfaces in the presence of IM-SAILs. It is found that the variations in both aliphatic chain length and number can remarkably change the trigger points of the orientational transition of LCs at the EAN/LC interface. Specifically, with a slight increase in the alkyl chain length of short-chained ILs, as the fluid medium, the orientation of LCs varied tremendously at the IL/LC interface. Therefore, the higher threshold concentration of IM-SAILs and the corresponding greater stability in the optical appearance of LCs at the EAN/LC interface compared to that of the aqueous/LC interface can be ascribed to the discrepancy in the microstructure of water and IL. Finally, we verified that the volume ratio of H2O to EAN could more dramatically affect the alignment of LCs than the change in IM-SAIL concentration in aqueous solution. This work first illustrated the impact of SAIL structure on the LCs orientation at the aqueous/LC, IL/LC, and H2O-IL mixture/LC interfaces, which will inspire us to obtain a stabilized molecular alignment of LCs at the IL/LC interfaces and to further design novel functionalized SAIL molecules for various chemical and biological applications.

Aggregation Behavior of Imidazolium-Based Surface-Active Ionic Liquids with Photoresponsive Cinnamate Counterions in the Aqueous Solution.

Two imidazolium-based surface active ionic liquids (SAILs) with photoresponsive cinnamate aromatic counterions, viz. 1-dodecyl-3-methylimidazolium cinnamate ([C12mim][CA]) and 1-dodecyl-3-methylimidazolium para-hydroxy-cinnamate ([C12mim][PCA]), were newly synthesized, and their self-assembly behaviors in aqueous solutions were systematically explored. Results of surface tension and conductivity measurements show that both [C12mim][CA] and [C12mim][PCA] display a superior surface activity in aqueous solutions compared to the common imidazolium-based SAIL, 1-dodecyl-3-methylimidazolium bromide (C12mimBr), which implies the incorporation of cinnamate aromatic counterions can promote the micellar formation. Furthermore, [C12mim][CA] shows higher surface activity due to the higher hydrophobicity of its counterion in comparison to [C12mim][PCA] that has a hydroxyl group. Both hexagonal liquid-crystalline phase (H1) and cubic liquid-crystalline phase (V2) were constructed in the [C12mim][CA] aqueous solutions. In contrast, the [C12mim][PCA]/H2O system only exhibits a single hexagonal liquid-crystalline phase (H1) in a broad concentration region. These lyotropic liquid crystal (LLC) phases were comprehensively characterized by polarized optical microscopy (POM), small-angle X-ray scattering (SAXS), and rheometer. Investigation on the temperature-dependent self-assembly nanostructures demonstrates that the higher temperature leads to a looser arrangement. Under UV irradiation, trans-cis photoisomerization of the phenylalkene group results in inferior surface activity of the prepared SAILs in aqueous solution with higher cmc values. Moreover, UV light irradiation induces obvious change of the structural parameters without altering the LLC phases. This work is expected to enrich the investigations of phase behaviors formed in SAILs systems and receive particular attention due to their unique properties and potential applications in drug delivery, biochemistry, materials science, etc.