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

The correlation between the micelle morphology of surface-active ionic liquids with self-assembly and thermodynamic characteristics: coarse-grained MD simulation and experiment

Surface-active ionic liquids (SAILs) show great promise as novel green solvents due to their low vapor pressure, high thermal stability, high electrical conductivity, and bio-friendly nature to replace traditional volatile organic solvents in industrial processes. In the present work, the combination of coarse-grained (CG) molecular dynamics (MD) simulations with conductivity measurements was employed to explain the correlation between the micelle morphology and physicochemical and thermodynamic properties of self-assembly. A homologous series of SAIL molecules, 1-n-alkyl-3-methylimidazolium bromide [Cnmim][Br] (n = 4, 6, 8, 10, and 12), were chosen at various concentrations to shed light on this issue. Simultaneously two factors of concentration and alkyl chain length affected the morphology to control the physical and thermodynamic features. Moreover, the nature of the headgroup for two SAILs with the longest alkyl chain was assessed by shifting from imidazolium into ammonium. First, the critical micelle concentration (CMC), the degree of counterion dissociation of micelles, and the standard Gibbs energy of micellization of SAILs were determined using conductivity data. The micelle morphology such as the aggregation number, micelle radius, and moment of inertia was computed before, around, and after the CMC by MD simulation. Simulated results in accordance with the experimental measurements provide a quantitative understanding of the micellar properties. Increasing the alkyl chain length was associated with a non-spherical bigger micelle while the ammonium-based surfactant with a lower repulsion between neighboring monomers in micelles induced bigger and more spherical aggregates. Raising the SAIL concentration did not considerably influence the sphericity of the micelle except for the SAIL with the longest tail. The umbrella sampling method calculated the potential of mean force (PMF) for pulling a monomer of SAIL from a pre-assembled micelle into the solution. The dissociation energy of a SAIL monomer from a micelle increased with the tail length or with shifting into the ammonium head group and was substantially influenced by micelle morphology. Comparison between a sphere micelle with an oval one demonstrated that the dissociation of a SAIL monomer from a non-spherical shape needed a higher amount of energy. An improved understanding of how the shape of the SAIL micelles controls the physicochemical properties and stability helps to extend their application to different chemical processes.

N-Alkylimidazolium carboxylates as a new type of catanionic surface active ionic liquid: synthesis, thermotropic behavior and micellization in water

Aiming at a new type of salt-free CASAIL (Catanionic Surface Active IL) for electrochemical applications or emulsifiers, dispersants, and foaming or antifoaming agents, we combined mesogenic anions (carboxylate) and cations (imidazolium) of similar shape and size to synthesize a series of congruent ion pairs of 1-alkyl-3-methylimidazolium alkylcarboxylates [Cnmim][Cm-1COO] (n = 10-16, m = 10-16). With particular focus on alkyl chain length varieties in both, imidazolium cations and carboxylate anions (n/m), the self-assembly in the bulk phase and in solution was investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), X-ray diffraction (XRD) experiments and surface tension measurements. Our results revealed that the presence of long alkyl chains on both the cation n and anion m leads to improved thermal stability of the bulk material while maintaining broad lamellar (SmA) mesophases. In water, we observed a strong and linear decrease of log(cmc) for increasing both the carboxylate anion and imidazolium cation chain length due to the increasing hydrophobic effect. Surprisingly, for both thermotropic behavior and micellization, the chain length of the carboxylate anion had a stronger impact than the chain length of the imidazolium cation, indicating its greater surface activity and tendency to form micelles.

Amphiphilic Ionic Liquids Capable to Formulate Organized Systems in an Aqueous Solution, Designed by a Combination of Traditional Surfactants and Commercial Drugs

The present review describes the state of the art in the conversion of pharmaceutically active ingredients (API) in amphiphilic Ionic Liquids (ILs) as alternative drug delivery systems. In particular, we focus our attention on the compounds generated by ionic exchange and without original counterions which generate different systems in comparison with the simple mixtures. In water, these new amphiphiles show similar or even better properties as surfactants in comparison with their precursors. Cations such as 1-alkyl-3-methyl-imidazolium and anions such as dioctyl sulfosuccinate or sodium dodecyl sulfate appear as the amphiphilic components most studied. In conclusion, this work shows interesting information on several promissory compounds and they appear as an interesting challenge to extend the application of ILs in the medical field.

Effect of the Substituent Position on the Phase Behavior and Photoresponsive Dynamic Behavior of Mixed Systems of a Gemini Surfactant and trans-Methoxy Sodium Cinnamates

Mixed systems of the Gemini cationic surfactant trimethylene-1,3-bis (dodecyldimethylammonium bromide) (12-3-12·2Br^-) and the photosensitive additives trans-methoxy sodium cinnamates with different substituent positions (trans-ortho-methoxy cinnamate, trans-OMCA; trans-meta-methoxy cinnamate, trans-MMCA; and trans-para-methoxy cinnamate, trans-PMCA) were selected for investigating the effects of the substituting position of methoxy on the system phase diagram and UV light-responsive behavior of the wormlike micelles. The differences in phase behaviors of the selected systems were analyzed by calculating the potential distribution, molecular volume, and free energy of solvation of cinnamates and the binding energies between photosensitive additives and the surfactant. The photoresponsive behaviors of wormlike micelle solutions formed in the selected systems were studied by the rheological method and UV-vis and H nuclear magnetic resonance (¹H NMR) spectroscopy; the kinetics of photoisomerization of trans-OMCA, trans-MMCA, and trans-PMCA were studied by first-order derivative spectrophotometry. The results reveal that the methoxy substituent position has a great influence on the phase behavior and photosensitivity of the studied systems. In addition, the photoisomerization of the studied cinnamates follows the first-order opposite reaction laws; the different reaction rates play the decisive role in the photosensitivity of the wormlike micelles. This paper would afford a deeper understanding of the UV light-responsive mechanism at the molecular level and provide essential guidance in preparing smart materials with adjustable light sensitivity.

Influence of the Alkyl Chain Length of the Imidazole Ionic Liquid-Type Surfactants on Their Aggregation Behavior with Sodium Dodecyl Sulfate

The influence of the alkyl chain length of the ionic liquid surfactants 1-hexadecyl-3-alkyl imidazolium bromide [C₁₆imC_n]Br (n = 2-16) on their aggregation behavior with sodium dodecyl sulfate (SDS) in water was studied. The rheological properties, thermostability, and microstructure of the samples were characterized via a combination of rheology, cryo-transmission electron microscopy, polarization optical microscopy, and small-angle X-ray scattering. Upon the addition of SDS, the [C₁₆imC_n]Br (n = 2, 4, 6) rodlike micelles transit into the gels with high water content. The effects of molar ratio and alkyl chain length on the viscoelasticity and thermal stability of the SDS/[C₁₆imC_n]Br (n = 2, 4, 6) gels were studied. However, the [C₁₆imC_n]Br (n = 8, 10, 12, 14, 16) rodlike micelles precipitate with the addition of SDS. The [C₁₆imC_n]Br (n = 10, 12, 14, 16) gels transit to the rodlike micelles with the proper addition of SDS. The mechanism of the influence of the alkyl chain length of the [C₁₆imC_n]Br on their aggregation behavior with SDS was proposed.

Molecular Dynamics Simulations and Density Functional Theory on Unraveling Photoresponsive Behavior of Wormlike Micelles Constructed by 12-2-12·2Br- and trans-ortho-Methoxy Cinnamate

Photoresponsive systems with controllable self-assembly morphologies and adjustable rheological properties have attracted widespread interest by researchers in the past few years. Among them, the photoresponsive systems consisting of ortho-methoxycinnamic (OMCA) and Gemini surfactants are endowed with rich self-assemblies with different states and in different scales including spherical micelles, wormlike micelles, vesicles, aqueous two-phase system (ATPS), etc. All these self-assemblies display excellent photoresponsive behavior. However, the mechanism of these photoresponsive behaviors has not been unraveled systematically so far. In this study, molecular dynamics (MD) simulations, density functional theory (DFT) calculations, transmission electron microscopy, and rheology are employed to investigate the photoresponsive behaviors of wormlike micelles caused by photoisomerization of trans-OMCA in 12-2-12·2Br^-/trans-OMCA solutions and to unravel the underlying mechanisms of these photoresponsive behaviors. The experimental results show that 12-2-12·2Br^-/trans-OMCA micelles display photoresponsiveness after UV-light irradiation, with the transformation of micellar morphologies from wormlike micelle to spherical micelles. In MD simulations, certain micelle morphologies in experiments and the specific packing between 12-2-12·2Br^-/OMCA were successfully captured. The larger three-dimensional structure and steric hindrance of cis-OMCA disturb the interior structure of micelles. The stronger hydrophilicity of cis-OMCA induces the escape of cis-OMCA from the interval of micelles to the solution. The energy results prove that trans-OMCA associates more strongly with 12-2-12·2Br^- than cis-OMCA. These causes lead to the fission and repacking of wormlike micelles.

Impact of Aromatic Counter-Ions Charge Delocalization on the Micellization Behavior of Surface-Active Ionic Liquids

The nature of counter-ions governs the micellar and structural characteristics of surface-active ionic liquids (SAILs). Especially, the introduction of aromatic counter-ions significantly increases their surface adsorption and induces the formation of various types of aggregates like prolate ellipsoidal micelles, rodlike micelles, vesicles, lamellars, etc. The present study reports the role of charge delocalization of two different aromatic counter-ions in the micellization behavior of their respective SAILs in aqueous medium. For this purpose, we have synthesized two SAILs, namely, 1-tetradecyl-3-methylimidzolium phenolate [C₁₄mim][PO] and 1-tetradecyl-3-methylimidzolium benzoate [C₁₄mim][BZ]. The O-atom of phenolate (PO^-) possesses negative charge, which is delocalized on its phenyl ring. Conversely, the negative charge of benzoate (BZ^-) is not delocalized on its phenyl ring. The more hydrophobic BZ^- counter-ion increases the hydrophobic interactions and reduces the electrostatic repulsions more efficiently as compared to PO^-, which results in a lower critical micelle concentration (cmc) of [C₁₄mim][BZ] than that of [C₁₄mim][PO]. Interfacial properties obtained by tensiometry reveal better surface activity and absorption efficiency of [C₁₄mim][BZ] as compared to [C₁₄mim][PO]. The increase of cmc and degree of counter-ion binding (β) with the rise of temperature for both SAILs has been observed by conductometry. The decrease in the polarity of pyrene microenvironment explains the higher compactness of [C₁₄mim][BZ] aggregates than that of [C₁₄mim][PO], observed by fluorimetry. The position of PO^- and BZ^- is in the stern and palisade layers of C₁₄mim⁺ aggregates, respectively, located by ¹H NMR. The existence of prolate ellipsoidal micelles for both SAILs has been established by small-angle neutron scattering measurements. Thus, the interfacial and bulk properties of [C₁₄mim][PO] lie somewhere in between those of the SAILs having perfect aromatic counter-ions, [C₁₄mim][BZ], and the SAILs having regular inorganic counter-ions like Cl^-, Br^-, etc.

A responsive anionic wormlike micelle using pH-directed release of stored sodium based on polybasic acids

Responsive wormlike micelles are very useful in a number of applications, whereas it is still challenging to create dramatic viscosity changes in anionic surfactant systems. Here a differential pH-responsive wormlike micelle based on sulfonic surfactants was developed, which is formed by mixing sodium dodecyl trioxyethylene sulphate (SDES) and ethylenediaminetetraacetic acid tetrasodium (EDTA4-·4Na+) at the molar ratio of 1 : 1. The phase behavior, aggregate microstructure and viscoelasticity of the SDES/EDTA4-·4Na+ solution were investigated via macroscopic observation, cryo-TEM and rheological measurements. It was found that the phase behavior of the SDES/EDTA4-·4Na+ solution undergoes transitions from a water-like fluid to viscoelastic upon decreasing the pH. On decreasing the pH from 12.01 to 3.27 by adding HCl, the viscosity of the transparent solutions with wormlike micelles was increased rapidly and reached ∼3100 mPa s. Furthermore, on increasing the pH by adding NaOH, the viscosity was slightly increased due to the addition of Na+. However, the increase in the concentration of Na+ is much smaller than the theoretical addition. The same phenomenon was noted in the sodium citrate solution, but does not exist in the sodium formate system. The viscosity of the micellar solution has a sensitive response to inorganic acids and tolerance to inorganic bases due to the characteristics of polybasic acids.

Smart Fluid System Dually Responsive to Light and Electric Fields: An Electrophotorheological Fluid

Electrophotorheological (EPR) fluids, whose rheological activity is dually responsive to light and electric fields (E fields), is formulated by mixing photosensitive spiropyran-decorated silica (SP-sSiO₂) nanoparticles with zwitterionic lecithin and mineral oil. A reversible photorheological (PR) activity of the EPR fluid is developed via the binding and releasing mechanism of lecithin and merocyanine (MC, a photoisomerized form of SP) under ultraviolet (UV) and visible (VIS) light applications. Moreover, the EPR fluid exhibits an 8-fold higher electrorheological (ER) performance compared to the SP-sSiO₂ nanoparticle-based ER fluid (without lecithin) under an E field, which is attributed to the enhanced dielectric properties facilitated by the binding of the lecithin and SP molecules. Upon dual application of UV light and an E field, the EPR fluid exhibits high EPR performance (ca. 115.3 Pa) that far exceeds its separate PR (ca. 0.8 Pa) and ER (ca. 57.5 Pa) activities, because of the synergistic contributions of the PR and ER effects through rigid and fully connected fibril-like structures. Consequently, this study offers a strategy on formulation of dual-stimuli responsive smart fluid systems.

UV and NIR dual-responsive self-assembly systems based on a novel coumarin derivative surfactant

Controllable self-assembly systems have attracted increasing attention in both the academic and industrial fields recently. Herein, we designed and synthesized a new photo-degradable anionic surfactant (PAS) with a coumarin group which could be degraded by both UV and NIR light. Thus, the micelles that are formed by sodium salts of PAS (PAS-Na) could be broken controllably under UV or NIR irradiation. Surface tension measurements, DLS, and Cryo-TEM were adopted to investigate the formation and disruption of PAS-Na micelles. PAS could also form wormlike micelles and vesicles when they co-assembled with common surfactant tetradecyldimethylamine oxide (C₁₄DMAO). These wormlike micelles and vesicles could be degraded by UV and NIR irradiation due to the participation of PAS. Accordingly, the rheology properties of the wormlike micelles and vesicles were also changed significantly. Finally, the stimulus-responsive system was used to control the diffusion of hydrophobic and hydrophilic molecules. And it has shown controllable release effects on both the hydrophobic and hydrophilic molecules.

Aggregation and Morphological Aptitude of Drug-Based Ionic Liquids in Aqueous Solution

Here, we present how replacing the usual inorganic counter ion with a pharmaceutically active aromatic one can greatly affect the interfacial as well as bulk properties of ionic liquids (ILs). We have synthesized a series of novel drug-based ILs, namely, 1-alkyl-3-methylimidazolium diclofenate ([C _n mim][DF]; n = 6, 8, 10, 12, and 14) abbreviated as DF-ILs, wherein DF^- is a well-recognized analgesic and nonsteroidal anti-inflammatory drug. We show strong synergistic interactions between C _n mim⁺ and aromatic DF^- attributed to reduced electrostatic repulsions and increased hydrophobicity from their incorporation, reflecting a 300-fold smaller critical aggregation concentration than that of their Cl^- analogue [C _n mim][Cl]. Interfacial properties for such strongly associating systems are discussed and clearly established to have remarkably improved properties than those of their Cl^- analogues. The decreasing polarity of the cybotactic region of pyrene with increase in the chain length "n" indicates an increased extent of packing of cationic head groups in the Stern layer. DF^- ion seems to play a vital role in the formation of the resulting aggregates, as probed by small angle neutron scattering and transmission electron microscopy. The thermodynamical insights of the aggregation process have been studied using isothermal titration calorimetry and temperature-dependent conductivity experiments. Unilamellar vesicles are formed at extremely low concentration, and also it is the first report that puts into picture the formation of vesicles for [C₆mim][DF] with such a short chain.

Nicotine-based surface active ionic liquids: Synthesis, self-assembly and cytotoxicity studies

New ester-functionalized surface active ionic liquids (SAILs) based on nicotine, [C_nENic][Br] (n=8, 10 and 12), with bromide counterions have been synthesized, characterized and investigated for their self-assembly behavior in aqueous medium. Conductivity measurements in aqueous solutions of the investigated SAILs have provided information about their critical micelle concentration (cmc), and degree of counterion binding (β), where cmc was found to be 2-3-fold lower than homologous SAILs or conventional cationic surfactants. The inherent fluorescence of SAILs in the absence of any external fluorescent probe have shed light on cmc as well as interactions prevailing between the monomers in micelle at molecular level. The thermodynamic parameters related to micellization have been deduced from isothermal titration calorimetry (ITC) and conductivity measurements. ¹H NMR, spin-lattice (T₁) relaxation time and 2D ¹H-^IH ROESY measurements have been exploited to get detailed account of internal structure of micelle. The size and shape of the micelles have been explored using dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. The synthesized SAILs have been found to be non-cytotoxic towards C6-Glioma cell line, which adds to the possible utility of these SAILs for diverse biological applications.

A pH-responsive wormlike micellar system of a noncovalent interaction-based surfactant with a tunable molecular structure

Responsive wormlike micelles are very useful in a number of applications, whereas it is still challenging to create dramatic viscosity changes in wormlike micellar systems. Here we developed a pH-responsive wormlike micellar system based on a noncovalent constructed surfactant, which is formed by the complexation of N-erucamidopropyl-N,N-dimethylamine (UC₂₂AMPM) and citric acid at the molar ratio of 3 : 1 (EACA). The phase behavior, aggregate microstructure and viscoelasticity of EACA solutions were investigated by macroscopic appearance observation, rheological and cryo-TEM measurements. It was found that the phase behavior of EACA solutions undergoes transition from transparent viscoelastic fluids to opalescent solutions and then phase separation with white floaters upon increasing the pH. Upon increasing the pH from 2.03 to 6.17, the viscosity of wormlike micelles in the transparent solutions continuously increased and reached ∼683 000 mPa s at pH 6.17. As the pH was adjusted to 7.31, the opalescent solution shows a water-like flowing behaviour and the η₀ rapidly declines to ∼1 mPa s. Thus, dramatic viscosity changes of about 6 magnitudes can be triggered by varying the pH values without any deterioration of the EACA system. This drastic variation in rheological behavior is attributed to the pH dependent interaction between UC₂₂AMPM and citric acid. Furthermore, the dependence on concentration and temperature of the rheological behavior of EACA solutions was also studied to assist in obtaining the desired pH-responsive viscosity changes.

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 ([C_nmim]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 [C_nmim]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.

Effect of an n-Alkoxy-2,4-hexadiene Polymerizable Tail System on the Mesogenic Properties and Cross-Linking of Mono-Imidazolium-Based Ionic Liquid Crystal Monomers

We demonstrate that an ether-based n-alkoxy-2,4-hexadiene polymerizable tail system is an effective and modular alternative to traditional ester-based polymerizable tail groups (i.e., acrylate, methacrylate, sorbate) and alkyl-1,3-diene tails for the design of radically polymerized ionic liquid crystal (ILC) monomers. Several series of nonsymmetric 1-vinylimidazolium-bromide-based ILC monomers containing these different polymerizable tail systems were synthesized and compared for their ability to form thermotropic liquid crystal (TLC) phases and to be photo-cross-linked with TLC phase retention. The n-alkoxy-2,4-hexadiene tail system was found to be more favorable/conducive to TLC phase formation than acrylate, methacrylate, and sorbate tails. It was more similar to the alkyl-1,3-diene tail system in terms of its more favorable effect on TLC behavior; however, it is more modular/easier to synthesize, more resistant to thermal Diels-Alder side reaction, and more isomerically pure, making it better for ILC monomer design. Also, the n-alkoxy-2,4-hexadiene tail system was found to be very amenable to radical photo-cross-linking with TLC phase retention. To demonstrate this feature, an example cross-linkable ILC monomer with this tail system was synthesized and polymerized in the smectic A TLC phase, and the monomer and polymerized material were characterized for their ionic conductivity behavior.

Light-responsive multillamellar vesicles in coumaric acid/alkyldimethylamine oxide binary systems: Effects of surfactant and hydrotrope structures

Herein, we report a series of novel light-responsive multilamellar vesicles based on the surfactant/hydrotrope binary systems. The phase behaviors of alkyldimethylamine oxide (CmDMAO, m=10, 12, 14) and trans-coumaric acid (trans-CA) isomerides, including trans-ortho-coumaric acid (trans-OCA), trans-meta-coumaric acid (trans-MCA) and trans-para-coumaric acid (trans-PCA), show that the multilamellar vesicle (MLV) formation region is commonly presented in the trans-CA/CmDMAO systems except trans-PCA/C12DMAO. Moreover, the molecular structures of CmDMAO and trans-CA affect the multilamellar vesicle formation region significantly. Generally speaking, the bigger the m, the larger the MLV region. Various techniques such as rheology, polarized optical microscopy (POM), (1)H NMR, (2)H NMR, cryogen transmission electron microscopy (cryo-TEM) and freeze-fracture transmission electron microscopy (FF-TEM) are used to characterize the aggregate structures. The multilamellar vesicles can transform into a homogeneous and transparent micelle phase or a two-phase system in the trans-OCA/CmDMAO binary systems under UV light irradiation, which depends on the chain length of CmDMAO and the molar ratio of [trans-OCA]/[CmDMAO]. Specifically, the light-stimuli response of multilamellar vesicles in the trans-OCA/C12DMAO system is representatively studied in detail. UV-vis spectra and (1)H NMR measurements illustrate that the light-induced trans-OCA to cis-OCA isomerization is essential during the transitions and the light-induced two-phase formation is attributed to the enrichment of surfactants, because the trans-cis isomerization can not only strengthen the hydrophilicity of cis-OCA but also increase the steric hindrance between cis-OCA and C12DMAO, and thereby altering the morphology of aggregate and the rheological response of bulk phase significantly.