Micellar Region Research Articles

Surface-active ionic liquids as drug carriers: A physico-chemical study

This work evaluates the potential of two surface active ionic liquids (SAILs) 1-dodecyl-3-methylimidazolium bromide and 1-tetradecyl-3-methylimidazolium bromide as drug carrier for ciprofloxacin (CPF) and compares them with their conventional counterparts dodecyltrimethylammonium bromide and tetradecyltrimethylammonium bromide using spectroscopic and electrochemical techniques. Different physico-chemical parameters including critical micelle concentration (CMC), binding constants, partition coefficients and their corresponding free energy changes, thermodynamic parameters of micellization and redox behavior of micelle-drug systems were investigated. Both the SAILs demonstrated higher solubilization powers and binding constants owing to the less polar nature of imidazolium ring. Lower CMCs indicated relatively stronger hydrophobic forces existing in all SAILs-CPF systems tested. The cyclic voltammetry displayed shifting of oxidation peaks towards higher positive potential in the micellar region indicating the protection of CPF against oxidation. This work demonstrates the benefits of using SAILs as drug carriers due to their lower CMCs, improved binding and partition coefficients, and favorable electrochemical results.

Synthesis, self-assembly and surface-active properties of alkyl halide mediated imidazolium monomeric surfactants

Two imidazolium monomeric surfactants, that is, 1-tetradecyl-1H-imidazole [14IM] and 1-hexadecyl-1H-imidazole [16IM] has been synthesized and characterized by 1H NMR,13C NMR, FTIR, HRMS spectroscopies and thermogravimetric analysis (TGA) for number and types of protons and carbon, functional groups, estimation of molecular weight and thermal stability of these compounds. The conductivity was measured in double distilled water at four different temperatures, 288, 293, 298, and 303 K. The results showed that these surfactants behave as weak electrolytes. The density and viscosity data have shown the existence of strong interactions between imidazolium surfactants and solvent (water) molecules. The results obtained from Root’s equation indicate that surfactant–solvent interactions are important than surfactant–surfactant interactions in dilute solutions, that is, below critical micellar concentration. The values of constants obtained from Einstein and Moulik equations have revealed that there was stronger and significant interaction between imidazolium surfactants and water molecules below critical micellar region. The surface tension parameters have indicated that these surfactants are good contenders to lower the surface tension of air/water interface. The results obtained from surface tension data have shown that standard change in free energy of micellization (ΔG°mic) and adsorption (ΔG°ads) were negative, indicating that these surfactants molecules have spontaneous tendencies to form micelles in solution at higher concentration and to get adsorb at the air/water interface at lower concentration. The TGA has indicated good thermally stability and activation energy for thermal decomposition was found in the range of 37.26.26–98.20.20 kJ/mol.

Diffusion of surfactant from a micellar solution to a bare interface. 1. Absorbing boundary

We analyze dynamic adsorption of surfactant from a micellar solution to a rapidly created surface that acts as an absorbing boundary for surfactant monomers (single molecules), along which the monomer concentration vanishes, with no direct micelle adsorption. This somewhat idealized situation is analyzed as a prototype for situations in which strong suppression of monomer concentration accelerates micelle dissociation, and will be used as a starting point for analysis of more realistic boundary conditions in subsequent work. We present scaling arguments and approximate models for particular time and parameter regimes and compare the resulting predictions to numerical simulations of the reaction–diffusion equations for a polydisperse system containing surfactant monomers and clusters of arbitrary aggregation number. The model considered here exhibits an initial period of rapid shrinkage and ultimate dissociation of micelles within a narrow region near the interface. This opens a micelle-free region near the interface after some time τe, the width of which increases as t1/2 at times t≫τe. In systems that exhibit disparate fast and slow bulk relaxation times τ1 and τ2 in response to small perturbations, τe is usually comparable to or greater than τ1 but much less than τ2. Such systems exhibit a wide intermediate time regime τe<t<τ2 in which the remaining micellar region reaches a state of partial local equilibrium, followed by a final stage t≫τ2 in which full local equilibrium is established.

Solubilization of Nile Red in Micelles and Protomicelles of Sodium Dodecyl Sulfate.

A spectrophotometric study of the solubilization and aggregation of the Nile red dye (NR) in premicellar and micellar aqueous solutions of sodium dodecyl sulfate (SDS) was carried out. The experiments were conducted both with saturated solutions of NR under conditions of thermodynamic equilibrium of the solution with a dye precipitate, and at a constant concentration of NR in a homogeneous solution. In the first case, it was proved theoretically and verified experimentally that with an increase in the SDS concentration, the NR concentration always increases, and at the limit of low concentrations, the dependence is linear. In both cases, the concentration of NR dimers as a function passes through a maximum in the premicellar region. There are no dimers in the micellar region. The extinction coefficients of NR monomers in SDS solutions were determined both below and above the critical micelle concentration (CMC) of SDS. A solubilization curve with branches for the premicellar and micellar regions was constructed, the intersection of which was used to find the CMC value in the system under study. The state of deep supersaturation of the NR solution in the metastable state upon dilution of the micellar system with water was studied. It was found that, in addition to dimers, molecular aggregates of higher orders were also formed.

In Ukrainian

Curcumin, a sparingly soluble polyphenol of plant origin, has antitumor, anti-inflammatory, antithrombotic, antidiabetic and antimicrobial properties. Currently, an important task is the development of medicinal composites based on curcumin, which provide an increase in its solubility and, accordingly, bioavailability. The aim of the work is to determine the optimal conditions for the adsorption of curcumin on the surface of a silica enterosorbent as soluble supramolecular complexes with a cationic dimeric surfactant decamethoxine. The UV/Vis spectroscopy data indicate that supramolecular interactions with decamethoxine lead to changes in the spectral characteristics of curcumin in solutions and on silica surface. The bathochromic shift of the absorption spectrum of curcumin in decamethoxine solutions characterizes the polarization of its carbonyl group in supramolecular complexes. The hypsochromic shift in the absorption spectra of curcumin adsorbed from decamethoxine solutions on silica is explained by the violation of its conjugated π-bond system, resulted probably from the change in the spatial orientation of the curcumin molecule at the adsorption of its complexes on the sorbent surface. Curcumin is adsorbed on highly dispersed silica much more effectively from decamethoxine solutions than from aqueous solutions. The adsorption of curcumin is maximal (92 %) at a concentration of decamethoxine 0.002 M, and decreases sharply to 9 % in the micellar region of concentrations (≥ 0.008 M). The dependence of curcumin adsorption on decamethoxine concentration is described by a domed curve, which indicates a significant contribution of hydrophobic interactions to the formation of supramolecular complexes of curcumin with cationic surfactant and their adsorption on silica surface. The results obtained are of practical importance and can be used in the development of new, more effective medicines containing bioactive curcumin, antiseptic decamethoxine and silica enterosorbent.

Solution Structures of Anionic-Amphoteric Surfactant Mixtures near the Two-Phase Region at Fixed pH.

We examine the solution structures in a mixed surfactant system of sodium dodecyl sulfate (SDS) and N,N-dimethyldodecylamine N-oxide (DDAO) in water, on both sides of the two-phase boundary, employing dynamic light scattering, small-angle neutron scattering, and Fourier transform infrared spectroscopy. The precipitate phase boundary was accessed by lowering pH to 8, from its floating pH 9.5 value, and was experimentally approached from the monomeric and micellar regions in three ways: at fixed DDAO or SDS concentrations and at a fixed (70:30) SDS:DDAO molar ratio. We characterize the size, shape, and interactions of micelles, which elongate approaching the boundary, leading to the formation of disk-like aggregates within the biphasic region, coexisting with micelles and monomers. Our data, from both monomeric and micellar solutions, indicate that the two phase structures formed are largely pathway-independent, with dimensions influenced by both pH and mixed surfactant composition. Precipitation occurs at intermediate stoichiometries with a similar SDS:DDAO ratio, whereas asymmetric stoichiometries form a re-entrant transition, returning to the mixed micelle phase. Overall, our findings demonstrate the effect of stoichiometry and solution pH on the synergistic interaction of mixed surfactants and their impact on phase equilibrium and associated micellar and two-phase structures.

Molecular Insight into Dye-Surfactant Interaction at Premicellar Concentrations: A Combined Two-Photon Absorption and Molecular Dynamics Simulation Study.

Both electrostatic and hydrophobic interactions play pivotal roles in ligand-surfactant binding interaction, especially for ionic surfactants. While much studies have been reported in the micellar region, less attention has been paid on such interactions at a low (premicellar) surfactant concentration. We here study the interaction between the cationic dye rhodamine 6G (R6G) with surfactants of different charge types: anionic SDS, cationic CTAB, and nonionic Tx 100 using absorption and emission spectroscopy. We identify that R6G forms dimeric aggregates at a premicellar concentration of SDS. Formation of aggregates is also confirmed from classical simulation measurements. CTAB and Tx 100 do not form any such aggregate, presumably owing to unfavorable electrostatic interactions. For a molecular-level understanding, we perform two-photon absorption (TPA) spectroscopy for the same systems. TPA allows us to calculate the two-photon absorption cross section and subsequently the change in the dipole moment (Δμ) between ground and excited states of the dye. We calculate the Δμ and observe that it passes through a maximum at a surfactant concentration half of the critical micelle concentration of SDS. This observation imparts support to earlier quantum mechanical calculation, which infers deviation from the parallel orientation of the dye during surfactant-induced aggregation. We extended our measurements and varied the carbon chain length of the anionic surfactant, and we found that all of them exhibit a maximum in Δμ, while their relative magnitude is dependent on the surfactant carbon chain length.

Studies of thermodynamics of micellization and pattern of self-association of decyltrimethylammonium bromide in aqueous solutions at 298.15 K

Using recently reported density, thermal coefficient of expansion and internal pressure data along with the literature osmotic coefficient and enthalpy data and adopting Mass–action model, the properties of decyltrimethylammonium bromide (C10TAB) in water are studied at 298.15 K. The number density, aggregation number, equilibrium constant, standard free energy changes due to micellization, standard entropy changes due to micellization and mean ionic activity coefficient are calculated in pre–micellar and post–micellar regions of concentration assuming that the cationic surfactant C10TAB is fully dissociated in water. Characteristic pattern of association are examined through the models/concepts developed by Tanford, Mukerjee as well as by O. P. Ts’o and noted that hydrophobic interactions between the non–polar chains and water structural effects (in the form of ion–solvent and ion–ion interactions) govern the equilibrium properties of such solutions. The critical micelle concentration (cmc) value and aggregation number value agree with the literature data. It has been observed that aggregation number value decreases slightly, equilibrium constant value goes through a minimum, standard free energy changes due to micellization parameter go through a maximum while positive magnitude of entropy changes due to micellization are observed as a function of concentration of C10TAB. The variation of mean ionic activity coefficient of the salt ions with concentration indicates deviation from ideal–associative solution behaviour. All these results are interpreted on the basis of monomer–micelle equilibria existing in solution phase, affecting the solution properties through electrostatic, hydrophobic solvation and hydrophobic interaction effects.

UV–Vis studies of methyl red in the presence of sodium dioctylsulfosuccinate/acetone and sodium dioctylsulfosuccinate/acetone/water

This paper reports the spectra of methyl red (MR) in the presence of sodium dioctylsulfosuccinate (AOT) by UV–Vis spectrophotometer at 298.15 ± 0.1 K. The experiment shows the effect of acetone, AOT and water concentration on methyl red. The spectral study was based on R parameter, which is defined as [H2O]/[AOT]. The spectral study was possible in the range of R = 0–20 only because the solution appeared to be cloudy above this amount of water. When the concentration of AOT increased, the absorption of MR decreased, indicating a hypochromic shift, which is due to the interaction between AOT and MR. The absorbance increases with the increasing value of R, which indicates that the H2O molecule hinders the interactional forces between AOT and MR. The distribution constant was calculated by using nonlinear regression analysis and its variation with different R values indicate the effect of water content in the distribution behavior of MR in between the solvent and micellar region whereas the variation of the binding constant with different R values indicates the affinity of micelles to bind MR molecule. The study of this binding affinity will be very helpful in textile dyeing, decolorization of industrial effluents and development of azo-based molecules in novel photonic and optoelectronic devices.

Spectroscopic study on the interaction of curcumin with single chain and gemini surfactants

Curcumin is a natural antioxidant and a polyphenol. The interaction of curcumin with different types of surfactants, (e.g., cationic gemini, anionic, nonionic and bile salt) in an aqueous medium has been studied spectrophotometrically and fluorimetrically in premicellar and post micellar concentration regions. Up to 0.095 mM concentration of cationic gemini surfactant (14-3-14), the absorbance value decreases and after that, increases. In the case of anionic SDMA and anionic sodium cholate (NaC), the absorbance value decreases up to 5.6 mM and 7.0 mM concentration respectively and then increases; after 11.0 mM concentration of SDMA and 17.0 mM concentration of NaC, the absorbance value becomes almost constant. For nonionic Mega 10, absorbance decreases initially and the peak is blue shifted to 371 nm. Then, with further addition of Mega 10, the absorbance value increases and the peak returns to its original position. After 7.4 mM concentration of Mega 10, the absorbance value becomes nearly constant. A fluorescence peak for Curcumin is observed at 537 nm. With increasing concentration of 14-4-14, initially, fluorescence intensity decreases up to 0.077 mM and then, fluorescence intensity increases and the spectra become gradually blue shifted to 501 nm. But for other surfactants used, fluorescence intensity increases with increasing concentration of surfactant and the spectra become gradually blue shifted and after the cmc, the intensity becomes constant. For 14-5-14, initially, anisotropy value increases and then decreases and after the cmc, this value again increases. In the case of SDMA, this value decreases with increasing concentration of SDMA up to 5.6 mM and then increases, after 13.5 mM, this becomes almost constant. For 212, no significant change of this value is observed. In the case of NaC, anisotropy value increases with increasing concentration of NaC and after 16.0 mM, it is almost constant. In the case of Mega 10, it decreases with increasing concentration of surfactant and above the cmc, becomes almost zero. In the premicellar region, curcumin forms complex with surfactant molecules and in the post micellar region, it is incorporated into the hydrophobic core of the micelle. The change in the intensity and wavelength of typical peaks in the absorption and the fluorescence spectra of curcumin shows a considerably different interaction behavior of surfactant molecules with curcumin.

Stimuli-Induced Nonequilibrium Phase Transitions in Polyelectrolyte-Surfactant Complex Coacervates.

Polyelectrolyte-surfactant complexes (PESCs) are important soft colloids with applications in the fields of personal care, cosmetics, pharmaceutics, and much more. If their phase diagrams have long been studied under pseudoequilibrium conditions, and often inside the micellar or vesicular regions, understanding the effect of nonequilibrium conditions, applied at phase boundaries, on the structure of PESCs generates an increasing interest. In this work we cross the micelle-vesicle and micelle-fiber phase boundaries in an isocompositional surfactant-polyelectrolyte aqueous system through a continuous and rapid variation of pH. We employ two microbial glycolipid biosurfactants in the presence of polyamines, both systems being characterized by their responsiveness to pH. We show that complex coacervates (Co) are always formed in the micellar region of both glycolipids' phase diagram and that their phase behavior drives the PESC stability and structure. However, for glycolipid forming single-wall vesicles, we observe an isostructural and isodimensional transition between complex coacervates and a multilamellar walls vesicle (MLWV) phase. For the fiber-forming glycolipid, on the contrary, the complex coacervate disassembles into free polyelectrolyte coexisting with the equilibrium fiber phase. Last but not least, this work also demonstrates the use of microbial glycolipid biosurfactants in the development of sustainable PESCs.

Distribution of benzalkonium chloride into the aqueous phases of submicron dispersed systems: emulsions, aqueous lecithin dispersion and nanospheres

Partitioning of benzalkonium chloride (BAC) into the aqueous phases of submicron dispersed systems such as submicron emulsions, aqueous lecithin dispersion (WLD), and suspension of nanospheres (NLC) was studied. The aqueous phases of the investigated systems were obtained by ultracentrifugation and subsequently were subjected to ultrafiltration, which procedure allowed distinguishing between the fractions of free benzalkonium chloride (w) and those incorporated in the liposomal and micellar region (wlm). The fractions present in the oily phase and in the interphase of submicron emulsions were calculated. Despite the various composition of the investigated formulations and the initial concentration of BAC, w values were very small at 0.2–8.0%. The wlm value in submicron emulsions was increased by increasing the total concentration of preservative from 29.0 to 42.0%. Using polysorbate 80 instead of lecithin resulted in a distribution of BAC to aqueous–liposomal–micellar phase that was twice as high. The very low concentration of antimicrobial active form of benzalkonium chloride was analyzed in the aqueous phase of emulsions stabilized with lecithin as well as in aqueous lecithin dispersion and nanospheres (below 3%). Replacement of lecithin with polysorbate 80 in emulsions with polysorbate significantly increase (up to 8%) the fraction of benzalkonium chloride in the aqueous phase where microbial growth occurs.

Determining Critical Micelle Concentrations of Surfactants Based on Viscosity Calculations from Coarse-Grained Molecular Dynamics Simulations

Alternative methods for determining the critical micelle concentration (CMC) are proposed using coarse-grained molecular dynamics (MD) simulations. In the literature, the CMC value is commonly taken to be the “free” (unassociated) surfactant concentration in the presence of micellar aggregates given by MD simulations. In the present study, two surfactants with different head groups and the same alkyl tail, n-octyltrimethylammonium bromide (C8TAB) and sodium octyl sulfate (S8S), were used to calculate the CMC value. The CMC of surfactants can be calculated from the variation in the zero-shear-rate viscosity as a function of the surfactant concentration in both the premicellar and micellar regions. Linear slopes were obtained in both regions with increasing surfactant concentrations. The CMC values for C8TAB and S8S were determined from the intersection of the two lines and are in good agreement with experimental values.

Thermodynamic and spectroscopic studies on cationic surfactant tetradecyltrimethylammonium bromide in aqueous solution of trisubstituted ionic liquid 1, 2-dimethyl-3-octylimidazolium chloride at different temperatures

In this work, the effects on micellar behavior of long chain cationic surfactant tetradecyltrimethylammonium bromide (TTAB) upon the addition of trisubstituted ionic liquid (IL), 1, 2-dimethyl-3-octylimidazolium chloride [odmim][Cl] at temperatures, 298.15–318.15 K has been studied. Different techniques such as conductance, surface tension, fluorescence and 1H NMR have been employed to understand the interactional mechanisms. The values of critical micelle concentration (cmc) and various thermodynamic parameters have been calculated from conductivity measurements. The surface parameters like effectiveness of decrease in surface tension (Πcmc), minimum surface area occupied per surfactant monomer (Amin), maximum surface excess concentration (Γmax), and adsorption efficiency (pC20) have been evaluated by surface tension measurements. Micellar aggregation number (Nagg) has been determined by quenching of pyrene. Further to understand interactions in post micellar region, 1H NMR measurements have been performed. It has been observed that the lipophilicity of interacting ion modified the thermodynamic and aggregation properties of TTAB.

Molecular simulation of structure formation and rheological properties of mixtures of telechelic and monofunctional associating polymer

ABSTRACTWe study the phase behavior, the characteristic times, and the rheological properties under the steady shear flow of the mixtures consisting of telechelic and monofunctional associating polymers by a coarse‐grained molecular dynamics simulation. The mixtures form the transient networks, the closely packed spherical micelles, and the wormlike micelles. We confirm the molecular origins of the several characteristic times of the mixtures. The dependencies of the characteristic times on the composition ratio between telechelic and monofunctional associating polymers show good agreement with reported experimental results. Under the steady shear flow, the mixtures show the shear thinning induced by the change of the spatial configuration of the micelles. The telechelic associating polymers especially play an important role in connecting the micelles at the shear thinning regime and enhance the steady shear viscosity. Furthermore, at the wormlike micellar region, the mixtures show the second shear thinning initiated by the transformation of the association conformation of the telechelic associating polymers.

The Differential Spectroscopic Investigation of Partitioning of Reactive Dyes in Micellar Media of Cationic Surfactant, Cetyl Trimethylammonium Bromide (CTAB)

Abstract This manuscript reports the solubilization of two reactive dyes viz. reactive black-5 (RB-5) and reactive black-8 (RB-8) in the micellar media of cationic surfactant, cetyl trimethylammonium bromide (CTAB) by differential UV/visible spectroscopy. Absorption spectra of said dyes in the presence of CTAB provide strong evidence about dye–surfactant interaction. In premicellar region ion association pair is formed between dye and surfactant while in post micellar region dye molecules get accommodated within the micelles. The values of critical micelle concentration (CMC) of CTAB in the presence of dyes, partition coefficient; Kx , free energy of partition, ∆Gp , binding constant, Kb and free energy of binding, ∆Gb were determined and compared for both dyes. It is, thus, concluded that RB-5 is solubilized to greater extent than RB-8 because of its incorporation in palisade layer of micelle close to micelle-water interface.

The alkyl polyglucoside/fatty alcohol ratio effect on the formation of liquid crystal phases in binary systems

The present research focuses on the alkyl polyglucoside, a non-ionic surfactant, in combination with a fatty alcohol of the same chain length used as a co-surfactant. A series of solutions were prepared, with varying both APG/FA ratio and its concentration in water. Different structures were then obtained, depending on these two parameters: aqueous micellar solutions, normal hexagonal liquid crystalline phase, α-gel phase, as well as the mixture of normal hexagonal/α-gel phases. A specific term “auto-emulsion” was introduced to describe the pseudo emulsions formed by the APG≤FA containing solutions because of the fatty alcohol, which dispersion in water was similar to an emulsion representation. The presence of the liquid crystals was revealed by optical microscopy under the polarized light, as different anisotropic conformations corresponding to the lamellar phase, the hexagonal phase and the coexistence of the lamellar and hexagonal phases, mainly for the most concentrated samples, were observed. These structures were characterized at the molecular level through the wide-angle X-ray diffraction technique and their macroscopic behaviour was investigated by rheology tests. Two main observations were then made: the variation of the surfactant concentration in solution promotes the transition between micellar region towards the liquid crystalline formation zone, while the APG/FA ratio impacts the formation of hexagonal phases (APG>FA) or of lamellar ones (APG<FA).

Solvatochromic betaine dyes of different hydrophobicity in ionic surfactant micelles: Molecular dynamics modeling of location character

In this paper, the locus and hydration character of three solvatochromic pyridinium-N-phenolate dyes in ionic surfactant micelles were examined using molecular dynamics modeling. These dyes, also called ‘betaine dyes’, are of various hydrophobicity due to different substituents in 2,6-positions of the phenolate moiety. They are as follows: 4-(2,4,6-triphenylpyridinium-1-yl)phenolate, 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl)phenolate, and 2,6-di-tert-butyl-4-(2,4,6-triphenylpyridinium-1-yl)phenolate; the abbreviations are BD-H, BD-Cl, and BD-tBu, respectively. The results were compared with those obtained previously with the so-called Reichardt’s standard betaine dye, 4-(2,4,6-triphenylpyridinium-1-yl)-2,6-diphenylphenolate, or BD-Ph. The aggregates of widely used ionic surfactants, sodium dodecyl sulfate, SDS, and cetyltrimethylammonium bromide, CTAB, were selected as the most typical micellar media. The results of modeling shed some light on the state of the solvatochromic dipoles within the micellar pseudophase. Though the location of the dyes is rather similar, with the phenolate oxygen atom directed toward the Stern layer, the more hydrophobic dyes, BD-tBu and BD-Ph, appeared to be immersed somewhat deeper as compared with BD-H and BD-Cl. The average compositions of the local microenvironments of the dye molecules and the hydration of the oxygen atom were estimated. The last finding confirms the higher values of the ET parameter of the interfacial micellar region of SDS as against those of CTAB, in line with experimental data. The versatile information concerning the dye locus was compared with the NMR data available in the literature. Also, the same studies were performed with the protonated colorless forms of the betaine dyes, keeping in mind that these compounds are also often used as acid-base indicators in micellar media. Noteworthy, for all of the dyes under study, and in both micelles, the protonated colorless forms are oriented somewhat different as compared with the corresponding colored dipolar molecules. This should be taken into account when utilizing these compounds as interfacial pH-probes, in particular, for estimating the surface electrical potential of micelles and other colloidal species.

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;...

Highly Viscoelastic Reverse Wormlike Micellar Systems from a Mixture of Lecithin, Polyglycerol Fatty Acid Monoesters, and an Oil.

We report new lecithin reverse wormlike micelles with high viscoelasticity formed using lecithin/polyglycerol fatty acid monoester (PGLFA)/oil systems. In this study, the influence of the amphiphilicity (i.e., hydrophile-lipophile balance, HLB) of PGLFA on the phase behavior and rheological properties of reverse wormlike micelles was investigated in detail. PGLFAs with degrees of polymerization of polyglycerol varying between 6-40 and constituent fatty acids with chains between 6-18 carbon atoms long were used. Partial phase diagrams of the lecithin/PGLFA/n-decane systems indicated that the appropriate PGLFA could change the lecithin/oil solution into a highly viscoelastic solution comprising reverse wormlike micelles. Rheological measurements showed that all systems that formed reverse wormlike micelles exhibited an unusual phenomenon called "shear-thickening". Furthermore, reverse wormlike micelles grew as the PGLFA concentration increased and the zero-shear viscosity (η0) of the solution rapidly increased. Our results indicate that the magnitude of the maximum η0 depends on the degree of polymerization of the constituent polyglycerol in the PGLFA, while the size of the reverse micellar region and the highly viscous region in the phase diagram depends on the HLB value of the PGLFA.