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.

Keggin-type polyoxometalate (POM), phosphotungstic acid (H3PW12O40), was encapsulated by an oppositely charged COOH-functionalized surface active ionic liquid (SAIL), N-decyl-N′-carboxymethyl imidazolium bromide ([N-C10, N′-COOH-Im]Br), with the assistance of an ionic self-assembly (ISA) process in an aqueous environment. The as-prepared POM/SAIL material possesses multiple active properties, including reversible pH-response and renewable catalyst for dye degradation. Specifically, the POM-based hybrid materials show a great enhancement in catalytic efficiency when it is employed in degradation of methyl orange (MO) in aqueous solution. Furthermore, the electrostatic repulsions between POM and the deprotonated SAIL may result in the pH-induced disassembly and assembly of the hybrid nanomaterials, which provides an expedient method to regenerate the catalytic activity. Therefore, the presented POM/SAIL hybrid materials are expected to improve the common poisoning issue of the traditional heterogeneous catalysts for industrial applications.Keywords: pH-Responsive; Polyoxometalate; Renewable catalyst; Self-assembly; Surface active ionic liquid;

We use an ionic self-assembly to build supramolecular catalysts using polyoxometalates (POM) and a common commercial surfactant with oppositely charged hexadecyltrimethylammonium bromide (CTAB). The supramolecular catalysts can dissolve in ionic liquid but become immiscible in water. On the basis of these properties, a new-style catalytic system was constructed by supramolecular catalysts and temperature-sensitive ionic liquid, tetrabutylphosphonium trifluoroacetate ([P4444][CF3COO]), in water. [P4444][CF3COO] aqueous solution can form a microemulsion at 298 K, and supramolecular catalysts can exist in the microemulsion phase. Phase separation occurs when the temperature is increased. So, the catalysts can be separated via the change in temperature. Moreover, supramolecular catalysts in ionic liquid can avoid poisoning in the catalytic process. This new-style catalytic system could be of great significance for cost savings in industry.Keywords: Heterogeneous catalysts; Ionic liquid; Photocatalysis; Polyoxometalates; Supermolecule;

The self-assembly behavior of an imidazolium-based catanionic surfactant, 1-butyl-3-methylimidazolium dodecylsulfate ([C4mim][C12H25SO4]), was investigated in water–ethylammonium nitrate (EAN) mixed solvents with different volume ratios. It is particular interesting that this simple surfactant could not only form lyotropic liquid crystals (LLC) with multimesophases, i.e., normal hexagonal (H1), lamellar liquid crystal (Lα), and reverse bicontinuous cubic phase (V2), in the water-rich environment but also act as an efficient low-molecular-weight gelator (LMWG) which gelated EAN-abundant binary media in a broad concentration range. The peculiar nanodisk cluster morphology of gels composed of similar bilayer units was first observed. FT-IR spectra and density functional theory (DFT) calculations reveal that strong H bonding and electrostatic interactions between EAN and the headgroups of [C4mim][C12H25SO4] are primarily responsible for gelation. The self-assembled gels displayed excellent mechanical strength and a thermoreversible sol–gel transition. It is for the first time that a rich variety of controllable ordered aggregates could be observed only by simply modulating the concentration of a single imidazolium-based catanionic surfactant or the ratio of mixed solvents. This environmentally friendly system is expected to have broad applications in various fields, such as materials science, drug delivery systems, and supramolecular chemistry.

The UV-light-stimulated self-assembly behavior of a surface active ionic liquid (SAIL), 1-hexadecyl-3-methylimidazolium bromide (C16mimBr), with an azobenzene derivative, sodium azobenzene 4-carboxylate (AzoCOONa), was investigated in aqueous solution. The properties and structures of the aggregates, formed at a concentration ratio equal to 2:1 ([C16mimBr]:[AzoCOONa]), were comprehensively characterized by rheometer and cryogenic transmission electron microscopy. Initially, viscoelastic wormlike micelles with a viscosity of 0.65 Pa·s were constructed in the C16mimBr/AzoCOONa system. Upon irradiation by UV light (365 nm), particularly fascinating is that the wormlike micelles become much longer and more entangled, exhibiting a high viscosity of 6.9 Pa·s. This can be attributed to photoisomerization of the AzoCOONa molecule from trans to cis form. It is the first time that, with exposure to UV or visible light, the aggregate type of the photoresponsive system has remained unchanged, with only a change of internal property parameters. The cation−π interaction prevailing over the hydrophobic interaction and electrostatic interaction between C16mimBr and AzoCOONa molecules is supposed to be responsible for this peculiar phase behavior. The wormlike micelles constructed with the SAIL and photosensitive additive exhibit controllable viscoelastic behavior in the photoresponsive process. In addition, the average contour length of wormlike micelles was found to slightly decrease with the increase of temperature. We expect this system will receive particular attention due to its unique properties and potential applications in drug delivery, biochemistry, and materials science, etc.

•A polyoxometalate-based supramolecular chemsensor CSS has been synthesized.•The supramolecular chemsensor CSS can selectively detect H2S with negligible responsive time (second level).•The chemsensor response to H2S with dual signals: fluorescence and absorption spectra.Hydrogen sulfide (H2S) has been verified as an important biological mediator in human physiological activities, but its rapid and accurate detection is remaining a challenge. Based on our early work, Eu-containing polyoxometalate/ionic liquid-type gemini surfactant hybrid nanoparticles fabricated by EuW10O36·32H2O (Eu-POM) and 1,2-bis(3-hexadecylimidazolium-1-yl) ethane bromide ([C16-2-C16im]Br2) via ionic self-assembly (ISA) strategy, we modified the hybrids with copper (II) ion and used them as a novel turn-off supramolecular fluorescence probe for H2S immediate response. Although copper (II) ions can cause decrease of the fluorescence intensity, the probe with moderate amount of copper (II) still has a high performance in emission property. The copper (II) ion-modified supramolecular sensor (CSS) shows dual signals in the fluorescence intensity and absorbance for H2S detection, and the detection limit is about1.25 μM. Furthermore, CSS displays high selectivity for H2S in the presence of other anions and species (e.g. Cl−, Br−, I−, SO42−, SO32−, S2O32−, AC−, H2O2, HCO3−, l-cysteine, homocysteine and l-glutathione), and also have potential for preferential imaging in vivo. Besides, the fluorescence quenching mechanism of CSS in the presence of H2S was explored. CuS generated by the reaction between Cu2+ and H2S was testified to act as a quencher, and the nonradiative resonance energy transfer mechanism was speculated to be responsible for fluorescence quenching. It is anticipated that the as-prepared CSS will be used as an efficient chemosensor for the rapid detection of H2S, which is critical for the diagnosis of some diseases, e.g. Alzhermer’s disease, Down’s syndrome, and diabetes, etc.A supramolecular fluorescence chemsensor used for H2S detection was built by modifying Cu2+ on the surface of supramolecular particles, and the quenching mechanism of generated CuS was explored.

•The synthesis and aggregation of pyrrolidinium-based SAIL were investigated.•Hexagonal phases were constructed in H2O-rich environment.•Lamellar gels were attained in EAN-abundant solvent.•Gels formed at different concentrations have nearly constant interlayer spacing.•H1 phase has a lower distance between cylinders at higher SAIL concentration.Pyrrolidinium-based surface active ionic liquid (SAIL), N-butyl-N-methylpyrrolidinium dodecyl sulfate ([C4MP][C12H25SO4]), was synthesized and its aggregation behavior was regulated by varying the concentration of SAIL and composition of H2O-ethylammonium nitrate (EAN) mixed solvent. Particularly interesting is that [C4MP][C12H25SO4] could not only form diverse lyotropic liquid crystals (LLCs), viz. hexagonal (H1) and lamellar liquid crystal (Lα) phases, in the water-rich environment, but also serve as an effective small molecule gelator and construct weak gel (W) and gel (G) in EAN-abundant binary solvent. The microstructures of LLC phases (H1 and Lα phases) were observed by polarized optical microscopy (POM). Small-angle X-ray scattering (SAXS) results affirm that the gels formed by different concentration of SAIL have the nearly constant interlayer spacing, and the H1 phase at higher [C4MP][C12H25SO4] concentration has a lower distance between the neighboring cylinders. Rheological measurements testify that the viscoelasticity of LLC phase reduces with the increasing content of EAN in the mixed solvent whereas increases with increase in concentration of SAIL. This work provides new insights into the aggregation behavior of SAILs in mixed solvents and the aggregates investigated may have potential applications in some fields, e.g. materials preparation and drug delivery, etc.A schematic illustration of aggregates formed by [C4MP][C12H25SO4] in H2O-EAN binary solvents.

•A novel approach to detect pesticides using liquid crystal droplet patterns.•The detection limit of the baycarb is around 0.01 pg.•The detection limit of the dimethoate is around 0.1 pg.•The liquid crystal sensing platform decorated with cationic surfactant.•This low-cost and label-free platform is quite convenient and sensitive.The alignment of liquid crystal (LC) is known to be sensitive to the properties of a bounding interface. Here, we report a LC droplet pattern platform based on enzymatic event of acetylcholinesterase (AChE) for sensitive detection of pesticides. In this method, the dark cross appearances of LC droplet patterns are obtained due to the formation of myristoylcholine (Myr) monolayer at the aqueous/LC interface after transferring Myr solution, which is corresponding to the perpendicular alignment of LC molecules at the interface. On the one hand, AChE mediates the hydrolysis of Myr to disrupt the surfactant monolayer, and the process leads to the bright fan-shaped images of LC droplet patterns when in contact with the pre-incubated mixture of AChE and Myr, which is indicating a planar orientation of LCs at the interface. On the other hand, the hydrolysis of Myr is inhibited in the presence of AChE-inhibiting pesticides such as baycarb and dimethoate, as a result, the LC droplet patterns present the dark cross appearances. On the basis of the principle, the LC droplet patterns could be utilized as an effective method to detect the pesticides. The results demonstrated that the LC droplet patterns were sensitive to baycarb with a detection limit of 1 ng/mL and dimethoate with a detection limit of 0.1 ng/mL. The constructed LC-based sensing platform is quite simple and convenient, and shows high promise for label-free detection of pesticides with very high sensitivity.

•The role of different substituent group on aromatic counterions was investigated.•Both of C12mimB than C12mimA exhibit lower cmc.•Interaction energy of SAIL-H2O complex calculated by DFT.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.A schematic illustration of aggregates formed by C12mimA and C12mimB in aqueous solution.Download high-res image (119KB)Download full-size image

•A label-free LC-based sensor with high selectivity and sensitivity for protein detections.•Three proteins including lysozyme, Con A and BSA are detected based on three different mechanisms.•A nonionic surfactant-decorated liquid crystal interface as the sensing platform.•The surfactant monolayer is stable regardless of pH and ionic strength in a wide range.Proteins are responsible for most biochemical events in human body. It is essential to develop sensitive and selective methods for the detection of proteins. In this study, liquid crystal (LC)-based sensor for highly selective and sensitive detection of lysozyme, concanavalin A (Con A), and bovine serum albumin (BSA) was constructed by utilizing the LC interface decorated with a nonionic surfactant, dodecyl β-d-glucopyranoside. A change of the LC optical images from bright to dark appearance was observed after transferring dodecyl β-d-glucopyranoside onto the aqueous/LC interface due to the formation of stable self-assembled surfactant monolayer, regardless of pH and ion concentrations studied in a wide range. The optical images turned back from dark to bright appearance after addition of lysozyme, Con A and BSA, respectively. Noteworthy is that these proteins can be further distinguished by adding enzyme inhibitors and controlling incubation temperature of the protein solutions based on three different interaction mechanisms between proteins and dodecyl β-d-glucopyranoside, viz. enzymatic hydrolysis, specific saccharide binding, and physical absorption. The LC-based sensor decorated with dodecyl β-d-glucopyranoside shows high sensitivity for protein detection. The limit of detection (LOD) for lysozyme, Con A and BSA reaches around 0.1 μg/mL, 0.01 μg/mL and 0.001 μg/mL, respectively. These results might provide new insights into increasing selectivity and sensitivity of LC-based sensors for the detection of proteins.

In water, Eu-containing polyoxometalate/gemini surfactant hybrid spheres with long emission timescale (3.758 ms) and high fluorescence quantum yield (25.17%) behaviors were synthesized. The hybrid spheres can be used as a bioprobe to image living cells.

We report fabrication, characterization, and potential applications of polyoxometalate (POM)/ionic liquid (IL) supramolecular spheres in water for the first time. These supramolecular spheres have highly ordered structures and show excellent reversible self-assembly and tunable photoluminescence properties, which can be manipulated by adjusting pH of the aqueous solution. Specifically, the formation of POM/IL supramolecular spheres results in quenching of fluorescence emitted by Eu-POM because hopping of the d1 electron in the POM molecule is blocked by hydrogen bond existing between the oxygen atom of POM and the carboxylic acid group of IL. However, the fluorescence can be completely recovered by gradually increasing pH of the aqueous solution due to the pH-induced deprotonation of the carboxylic acid group of IL, which results in disassembly of the fabricated supramolecular spheres. Applications of these stimuli-responsive photoluminescent POM-based supramolecular materials are demonstrated in biological media. Dual signaling responses of turbidity and fluorescence are observed simultaneously in the detection of urease and heavy metals based on pH-induced disassembly of the supramolecular spheres during the biochemical events in aqueous solution. In addition, guest molecules are encapsulated into the supramolecular spheres, and controlled release of these entrapped molecules is demonstrated in the presence of external stimuli. This study shows potential of stimuli-responsive POM/IL supramolecular materials in biological applications.

•A novel method to monitor cellulase and cysteine using liquid crystals.•The sensing platform is based on enzymatic activity and reactivation.•The detection limit of cellulase is around 0.00001 mg/mL in a solution of cysteine.•The detection limit of cysteine is around 82.5 μM.•The label-free and simple platform is quite sensitive and low-cost.A liquid crystal (LC)-based sensor, which is capable of monitoring enzymatic activity at the aqueous/LC interface and detecting cellulase and cysteine (Cys), was herein reported. When functionalized with a surfactant, dodecyl β-d-glucopyranoside, the 4-cyano-4′-pentylbiphenyl (5CB) displays a dark-to-bright transition in the optical appearance for cellulase. We attribute this change to the orientational transition of LCs, as a result of enzymatic hydrolysis between cellulase and surfactant. Furthermore, by adding cellulase and Cu2+, our surfactant-LCs system performs an interesting ability to detect Cys, even though Cys could not interact with surfactant or LC directly. Alternatively, through the strong binding between Cys and Cu2+, cellulase was able to hydrolyze surfactant in the presence of Cu2+, leading to the transition of LCs from dark to bright. The detection limit of the LC sensor was around 1 × 10−5 mg/mL and 82.5 μM for cellulase and Cys, respectively. The LC-based sensor may contribute to the development of low-cost, expedient, and label-free detection for cellulase and Cys and the design strategy may also provide a novel way for detecting multiple analytes.Schematic representation of the detection process for cellulase and cysteine. &z.rtrif; 5CB: 4-cyano-4′-pentylbiphenyl.

A supramolecular gel was constructed by using an imidazolium-based surfactant, N-cetyl-N′-carboxymethyl imidazolium bromide ([N-C16, N′-CO2H-Im]Br), in the DMSO/H2O binary solvent mixtures and investigated as an adsorbent for removing dyes from aqueous solution. The self-assembled gel displays a morphology of microplatelets stacked in bilayer units with interdigitated hydrocarbon tails, and the structure remains unchanged below the sol–gel transition temperature. The gel also exhibits a strong birefringence property and excellent mechanical strength. In particular, the gels show superior performance in removal of anionic dye molecules, for example, removing 80% of eosin Y within 10 min, The constructed gels also present excellent salinity tolerance, even when the concentration of NaCl is 1000 times higher than that of the dye, and can maintain their high efficiency after 25 cycles, indicative of their promise in water treatment.Keywords: anionic dye; high mechanical strength; selective removal; supramolecular gel;

The ionic liquid (IL), tetrabutylphosphonium trifluoroacetate ([P4444][CF3COO]), showed a low critical solution temperature (LCST)-type phase transition in water. Using this temperature-sensitive IL and the Triton X-100/H2O system, the reversible transformation between micelles and microemulsions was thus realized by a thermal stimulus for the first time.

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

The self-aggregation behavior of catanionic surface active ionic liquids (SAIL), 1-alkyl-3-methylimidazolium alkyl sulfates, [C4mim][C16SO4] and [C6mim][C14SO4], in aqueous solutions was explored by several techniques. These results were analyzed together with the concerning data of [C8mim][C12SO4] reported previously. The feature of these SAIL is that the total carbon number of the hydrophobic chains is kept constant, while only the length of the two hydrocarbon chains varies. Because of the different intermolecular and intramolecular interactions, the hydrophobic interaction of asymmetrical SAIL is enhanced, which explains the minimal CMC value of [C4mim][C16SO4]. Thermal motion of hydrocarbon chains at the air–water interface leads to higher Amin and lower Γmax values with the increasing asymmetry of two hydrophobic chains. The conductivity measurements reveal that the micellization process is spontaneous and entropy-driven in the studied temperature range. This work indicates that the symmetry of alkyl chains can influence the aggregation behavior of [Cnmim][CmSO4] in aqueous solutions.

In this report, multiple-stimulus-responsive materials were synthesized via supramolecular self-assembly. One-dimensional nanorods were constructed by the self-aggregation of 4-(phenyl-azo)benzoic acid (PBA) molecules in aqueous solution at pH 3.2. As the pH of the solution was increased to 6.5, these nanorods transformed into two-dimensional polygons. Upon UV irradiation, the as-prepared nanorods disappeared completely, and nanospheres were subsequently obtained. On the basis of the weak interactions between PBA and additive molecules, for example, N-alkyl-N′-carboxymethyl imidazolium bromide, β-cyclodextrin, and cetyltrimethylammonium bromide, materials with various morphologies were also fabricated by a surfactant-assistant self-assembly strategy. Noteworthy is that Salvia officinalis-shaped material is among them. To the best of our knowledge, this type of microstructured material has been rarely reported. In addition, slender fibers, sphere-like particles, and aggregates of spheres were also observed. These results suggest that the rational fabrication of materials with desired shapes and sizes can be achieved by changing external environments during the self-aggregation of PBA molecules. Both cyclic voltammogram experiments and density functional theory calculations exhibit the optoelectronic behavior of these materials, which is expected to have potential applications in the fabrication of photoelectronic nanodevices.

Two imidazolium-based surface-active ionic liquids with aromatic counterions, namely, 1-dodecyl-3-methylimidazolium salicylate (C12mimSal) and 1-dodecyl-3-methylimidazolium 3-hydroxy-2-naphthoate (C12mimHNC), were synthesized, and their aggregate behavior in aqueous solutions was systematically explored. Surface tension and conductivity measurements indicate that both C12mimSal and C12mimHNC show superior surface activity compared to the common imidazolium-based SAIL with the same hydrocarbon chain length, 1-dodecyl-3-methylimidazolium bromide (C12mimBr). This result demonstrates that the incorporation of aromatic counterions favors the formation of micelles. C12mimHNC displays a higher surface activity than C12mimSal, resulting from the different hydrophobicities of the counterions. In comparison with C12mimBr, C12mimSal not only can form hexagonal liquid-crystalline phase (H1) in aqueous solution, but also exhibits a broad region of cubic liquid-crystalline phase (V2) at higher concentration. As for the C12mimHNC/H2O system, a lamellar liquid-crystalline (Lα) phase was observed. These lyotropic liquid crystals (LLCs) were characterized by polarized optical microscopy (POM) and small-angle X-ray scattering (SAXS). Structural parameters calculated from SAXS patterns suggest that a higher concentration of the SAIL leads to a denser arrangement whereas a higher temperature results in the opposite effect. The rheological results manifest that the formed H1 phase in the C12mimSal/H2O system exhibits an impressive viscoelastic behavior, indicated by a modulus (G′ and G″) that is 1 order of magnitude higher than that of C12mimBr. Density functional theory (DFT) calculations reveal that C12mimSal has a more negative interaction energy with a water molecule and the Sal– counterion presents a stronger electronegativity than the HNC– counterion. The specific phase behavior of the C12mimSal/H2O and C12mimHNC/H2O systems can be attributed to the strong synergic interaction between the imidazolium cation and the aromatic counterion, including electrostatic attraction, hydrophobic interaction, and especially π–π interaction.

The aggregation behavior of surface-active ionic liquids (SAILs) 1-dodecyl-3-methylimidazolium m- and p-hydroxybenzoate (m-C12mimHB and p-C12mimHB) in water and ethylammonium nitrate (EAN) was investigated. Surface tension measurements indicate that the cmc values of SAILs in EAN are much higher than those in water, resulting from the weaker solvophobic effect of EAN, and the stronger stability of SAILs/EAN complexes proven by DFT calculations. Compared to 1-dodecyl-3-methylimidazolium salicylate (C12mimSal), the effect of substituent position leads to weaker interactions between aromatic counterions and headgroups. The hexagonal liquid crystal (H1) phase formed by C12mimHB in water or EAN at a higher concentration was determined by polarized optical microscopy (POM), small-angle X-ray scattering (SAXS), and rheology techniques. Structural parameters estimated from SAXS curves suggest that the higher SAILs concentration or temperature leads to a smaller lattice parameter (a0) and a denser arrangement of cylinders. For C12mimHB, the formation of the H1 phase in H2O is easier than that in EAN. Furthermore, compared to C12mimSal, C12mimHB exists over a broad region of the hexagonal liquid crystalline (H1) phase, which is due to the different position of the substituents on the aromatic ring of counterions. Therefore, the H1 phase of the lypotropic liquid crystals (LLCs) formed in the C12mimHB/H2O system exhibits excellent performance in uniformly dispersing multiwalled carbon nanotubes (MWCNTs). Increasing the concentration of MWCNTs results in a larger lattice parameter (a0) value, indicating the integration of MWCNTs within the cylinders of the H1 phase. The rheological measurement results demonstrate that MWCNTs/LLCs composites are highly viscoelastic, and the presence of MWCNTs obviously strengthens the apparent viscosity of the H1 phase.

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.

•A novel approach to detect acetylcholinesterase and its inhibitor using liquid crystals.•The cationic surfactant-decorated liquid crystal interface is used as the sensing platform.•This low-cost and label-free strategy is quite simple and highly sensitive.•The detection limit of the enzyme is around 0.000827 U/mL in a serum albumin solution.•The detection limit of the enzyme inhibitor is around 1 fM.In this paper, construction of the liquid crystal (LC)-based sensing platform for simple and sensitive detection of acetylcholinesterase (AChE) and its inhibitor using a cationic surfactant-decorated LC interface was demonstrated. A change of the optical images of LCs from bright to dark appearance was observed when the cationic surfactant, myristoylcholine chloride (Myr), was transferred onto the aqueous/LC interface, due to the formation of a stable surfactant monolayer at the interface. A dark-to-bright change of the optical appearance was then observed when AChE was transferred onto the Myr-decorated LC interface. The sensitivity of this new type of LC-based sensor is 3 orders of magnitude higher in the serum albumin solution than that only in the buffer solution. Noteworthy is that the AChE LC sensor shows a very high sensitivity for the detection of the enzyme inhibitor, which is around 1 fM. The constructed low-cost LC-based sensor is quite simple and convenient, showing high promise for label-free detection of AChE and its inhibitors.

The ionic liquid (IL), tetrabutylphosphonium trifluoroacetate ([P4444][CF3COO]) showed a low critical solution temperature (LCST)-type phase transition in water. It was found that [P4444][CF3COO] molecules can form some kind of long-living aggregates in aqueous solution under certain conditions before the phase separation. These aggregates displayed the characteristic properties of microemulsions, although no surfactants are used. For instance, the aggregate droplet size can be adjusted by temperature and concentration, which behaves like the swelling phenomenon of microemulsions; the formed aggregates showed beneficial solubilization capacity for apolar substances; in addition, a tunable micropolarity in the aggregates text-decoration:underline"-Vis measurements. These are by far the simplest aggregates having the microemulsion characteristics. In nature, these microemulsion-like aggregates have mesoscopic phase separation, which is the intermediate state for macroscopic phase separation. This special system can be regarded as surfactant-free microemulsion-like aggregates and should be an effective platform to provide novel extraction or separation media.

The self-assembly behavior of an imidazolium-based catanionic surfactant, 1-butyl-3-methylimidazolium dodecylsulfate ([C4mim][C12H25SO4]), was investigated in water–ethylammonium nitrate (EAN) mixed solvents with different volume ratios. It is particular interesting that this simple surfactant could not only form lyotropic liquid crystals (LLC) with multimesophases, i.e., normal hexagonal (H1), lamellar liquid crystal (Lα), and reverse bicontinuous cubic phase (V2), in the water-rich environment but also act as an efficient low-molecular-weight gelator (LMWG) which gelated EAN-abundant binary media in a broad concentration range. The peculiar nanodisk cluster morphology of gels composed of similar bilayer units was first observed. FT-IR spectra and density functional theory (DFT) calculations reveal that strong H bonding and electrostatic interactions between EAN and the headgroups of [C4mim][C12H25SO4] are primarily responsible for gelation. The self-assembled gels displayed excellent mechanical strength and a thermoreversible sol–gel transition. It is for the first time that a rich variety of controllable ordered aggregates could be observed only by simply modulating the concentration of a single imidazolium-based catanionic surfactant or the ratio of mixed solvents. This environmentally friendly system is expected to have broad applications in various fields, such as materials science, drug delivery systems, and supramolecular chemistry.

•Aggregation behavior of AOT- and DEHP-based surfactants in aqueous solution was systematically studied.•Theoretical calculations were used to explain the experimental results.•Surface activity of these SAILs is superior to their sodium analogs.•Surface properties are controlled by the structure of surface active group rather than counterions.Two structurally similar imidazolium-based anionic surface active ionic liquids (SAILs) with double hydrocarbon chains, viz. 1-butyl-3-methylimidazolium bis(2-ethylhexyl) sulfosuccinate (C4mim-AOT) and 1-butyl-3-methylimidazolium bis(2-ethylhexyl) phosphate (C4mim-DEHP), were synthesized by a straightforward ion-exchange technique. A comparative investigation of their aggregation behavior with the corresponding traditional anionic surfactants, sodium bis(2-ethylhexyl) sulfosuccinate (Na-AOT) and sodium bis(2-ethylhexyl) phosphate (Na-DEHP) in aqueous solution was performed in detail by surface tension, electric conductivity, fluorescence spectra and dynamic light scattering measurements. The critical micelle concentration (CMC) values for the surfactants with double hydrocarbon chains obtained by different techniques are in good agreement. The surface activity of C4mim-AOT and C4mim-DEHP is superior to that of the corresponding traditional anionic surfactants, Na-AOT and Na-DEHP. It is also found that for anionic SAILs the nature of the anionic active group is a dominant factor in the determination of their aggregation behavior in aqueous solution, e.g. CMC and aggregation number, while the introduced organic cation plays a minor role. Theoretical calculations show that more conformations and electronegativity for DEHP anion leads to higher aggregation number and CMC values for C4mim-DEHP. This work is expected to be of practical values for the environmental friendly anion SAILs in nanomaterial synthesis and phase separation, etc.Aggregation behavior of AOT- and DEHP-based surfactants in aqueous solution was studied systematically by various experimental techniques and theoretical calculation. Results indicate that surface activity of 1-butyl-3-methylimidazolium bis(2-ethylhexyl) sulfosuccinate (C4mim-AOT) and 1-butyl-3-methylimidazolium bis(2-ethylhexyl) phosphate (C4mim-DEHP) is superior to their sodium analogs, Na-AOT and Na-DEHP. The difference in the aggregation behavior between AOT- and DEHP-based surfactants was also investigated comparatively and attributed to their discrepancy in the characteristics of polar headgroups, such as electrostatic potentials and van der Waals volume of headgroups.

Halogen-free and low-cost alkylcarboxylate-based anionic surface active ionic liquids (SAILs), namely, 1-butyl-3-methylimidazolium alkylcarboxylates ([C4mim][CnH2n–1O2], n = 8, 10, 12), were first synthesized through the neutralization of imidazolium hydroxide by alkylcarboxylic acids. A systematic study of their self-aggregation behavior in water was investigated by surface tension, electrical conductivity, steady-state fluorescence quenching, and 1H NMR. The micellar properties of this series of SAILs in ethylammonium nitrate (EAN) were also studied by surface tensiometry for comparison. A set of surface active parameters and thermodynamic parameters of these compounds in water and EAN was obtained. Surface tension results show that the surface activity of [C4mim][CnH2n–1O2] in EAN is inferior to that in water. They exhibit a higher ability to aggregate in water than the traditional anionic surfactants, sodium alkylcarboxylates (SAC), and anionic SAILs, 1-butyl-3-methylimidazolium alkylsulfates ([C4mim][CnH2n+1SO4]) with the same hydrocarbon chain length. This demonstrates that the incorporation of carboxylate group and [C4mim]+ cation favors micelle formation. To understand the discrepancy in the surface activity of alkylsulfate- and alkylcarboxylate-based SAILs, theoretical calculations were performed to give electrostatic potential of the corresponding anions. The higher surface activity of [C4mim][C12H23O2] mainly originates from the lower electronegativity of its anion. Density functional theory (DFT) calculations manifest that the interaction energy of binary combination SAILs–EAN is larger than that of SAILs–H2O, implying the stronger interaction of the former. Consequently, it is more difficult for [C4mim][CnH2n–1O2] to self-aggregate in EAN than in H2O. This work is expected to be of practical value for the environmentally friendly alkylcarboxylate-based SAILs in some potential applications, including nanomaterials synthesis and phase separation, among others.

•Effect of various electrolytes on the aggregation behavior of an anionic halogen-free surfactant ionic liquid (SAIL) was studied.•Organic salts were superior to inorganic salts for promoting aggregation of the SAIL.•Hydrophobic played a predominant role in the salt effect.•Salt additives had no obvious effect on the size of aggregates.•Quantum chemical calculations were used to explain the experimental results.Effect of three inorganic electrolytes (LiCl, NaCl, and MgCl2) and four organic electrolytes, viz. tetraalkylammonium bromides ((CH3)4NBr, (C2H5)4NBr, (C3H7)4NBr, and (C4H9)4NBr) on the aggregation behavior of the anionic halogen-free surface active ionic liquid, 1-butyl-3-methylimidazolium dodecylsulfate ([C4mim][C12SO4]), in aqueous solution was studied by surface tension, steady-state fluorescence quenching, and dynamic light scattering measurements. The results show that all the electrolytes investigated have a salting-out effect, which promotes aggregate formation of [C4mim][C12SO4]. The stronger hydrophobicity of organic electrolytes is crucial for the superior influence on the surface activity of [C4mim][C12SO4]. However, the stabilization energy results obtained by quantum chemical calculations prove that although the promoting effect of organic cations (tetraalkylammonium cations) on the micellization process of [C4mim][C12SO4] is powerful, they mainly act as counterions. For a given electrolyte (i.e., NaCl), critical micelle concentration of [C4mim][C12SO4] decreases with increasing electrolyte concentration. The average aggregation number and aggregate size of [C4mim][C12SO4] were shown to change slightly in the presence of various electrolytes, except for MgCl2. Anyway, hydrophobicity together with bulkiness and hydration ability of cations of the added electrolytes are suggested to play important roles in modifying the aggregation behavior of [C4mim][C12SO4] in aqueous solution.

A novel class of zwitterionic surface active ionic liquids (SAILs), N-alkyl-N′-carboxymethyl imidazolium inner salts ([NCn, N′CO2Im], n = 10, 12, 14), was synthesized. Their aggregation behavior in aqueous solution was investigated by surface tension, isothermal titration calorimetry, and steady-state fluorescence. Compared with the reported imidazolium-based cationic SAILs, 1-alkyl-3-methylimidazolium bromide ([Cnmim]Br) and zwitterionic betaine surfactants, (CnH2n+1N(CH3)2CH2COO−), [NCn, N′CO2Im] exhibits significantly lower critical micelle concentration (cmc) and surface tension at cmc (γcmc) values. It is attributed to the incorporation of a deprotonated carboxylic group into the head group, which weakens the electrostatic repulsion between head groups and favors micellization. The micellar aggregation number of [NCn, N′CO2Im] is larger than that of [Cnmim]Br, while less than that of CnH2n+1N(CH3)2CH2COO−. Similar to the traditional zwitterionic surfactants, the surface activity and adsorption properties of [NC12, N′CO2Im] at air/water interface have a slight variation with temperature, pH, and ionic strength. This indicates that the present zwitterionic SAILs display the aggregation behavior much similar to zwitterionic surfactants, distinctly different from imidazolium-based cationic SAILs. Sets in low sensitivity to the environmental conditions, superior surface activity and unique physicochemical properties of ionic liquids, [NCn, N′CO2Im] can be exploited for utilizing as a potential substitute for conventional surfactants in certain fields.Graphical abstractHighlights► A novel class of zwitterionic surface active ionic liquids was synthesized. ► Their aggregation behavior in aqueous media was investigated systematically. ► They exhibit superior surface activity. ► They are stable against the variation of temperature, pH, and ionic strength.

•Salt-free surface active ionic liquids (SAILs) have been synthesized.•Both the cation and anion of these SAILs have surface activity.•These SAILs exhibit particularly high surface activity.•The alkyl chain length on both cation and anion was changed.•Alkyl chains of SAILs with higher asymmetry display higher surface activity.A series of salt-free catanionic surface active ionic liquids (SAILs), 1-alkyl-3-methylimidazolim alkyl sulfates (denoted as [Cnmim][CmSO4], n = 6, 8, 10; m = 12 and n = 4; m = 10, 14) were synthesized by an ion exchange reaction and their surface properties in aqueous solution were examined systematically by surface tension, fluorescence and electrical conductivity measurements. As catanionic surfactants, these SAILs exhibit notably higher surface activity, compared to the cationic or anionic analogues. Increment in both cationic and anionic alkyl chain lengths for [Cnmim][CmSO4] can both improve the amphiphilic character remarkably. This can be ascribed to cooperative interactions as formation of catanionic pairs between alkyl-substituted imidazolium cations and alkyl sulfate anions. The negative micellization Gibbs free energy values prove that the micellization of all the 1-alkyl-3-methylimidazolim alkyl sulfates investigated is a spontaneous process. Any additional CH2 group makes the micellization process easier regardless if it is on a cation or an anion. When keeping the total carbon atom number constant, we find that the [Cnmim][CmSO4] molecules with greater asymmetric alkyl chains display superior surface activity. This work indicates that the self-assembly of these imidazolium-based salt-free catanionic SAILs can be tailored by adjusting the mismatch of alkyl chains. These SAILs are expected to have potential applications in the fields of colloidal and interface and nanomaterial synthesis.

•The hxy values for amino acids–propanediol isomers are all positive.•The order of hxy values is hxy (propanediol) > hxy (glycol) > hxy (glycerol).•The number of OH groups for polyols affects hxy values strongly than the position.Mixing enthalpies of aqueous glycine, l-α-alanine, l-α-valine, l-α-serine. l-α-threonine and l-α-proline solutions and aqueous 1,2-propanediol and 1,3-propanediol solutions and their dilution enthalpies have been measured with a Thermometric-2277 Thermal Activity Monitor at 298.15 K. Experimental data were treated according to the McMillan–Mayer theory and the heterogeneous enthalpic pairwise interaction coefficients (hxy) of the natural amino acids and propanediol molecules in aqueous solution were obtained. Combining the hxy coefficients of amino acids with glycol and glycerol in aqueous solution reported by our previous works, the effects of number and position of OH groups in polyalcohols on the interactions between them and amino acids are discussed in the terms of solute–solute interactions.

Calcium carbonate (CaCO3) nanocrystals with controllable polymorph and morphology have been successfully synthesized with the aid of an effective control agent, a halogen-free, low-cost ionic liquid surfactant, 1-butyl-3-methylimidazolium dodecylsulfate ([C4mim][C12SO4]) in a supersaturated aqueous solution. For the first time, facile preparation of pure lens-like vaterite, sheet-like calcite, and peanut-like aragonite was all achieved in the [C4mim][C12SO4] aqueous solution through changing the concentration, temperature, and initial pH value and adding magnesium ions. Washed by water and ethanol, all the aggregates were free of [C4mim][C12SO4] and can be stable at least 1 month in air. The crystal form of the aggregates changed from pure calcite to pure vaterite at room temperature only through increasing [C4mim][C12SO4] concentration. Formation of the ordered CaCO3 structures is mainly ascribed to the aggregation of the primary nanoparticles whose formation mechanism is related to the change of supersaturation. This study can provide a facile and environment-friendly method to fabricate CaCO3 crystal aggregates with various morphologies and polymorphs and can be used for large-scale industrial production and biomimetic synthesis.

The crystallization of calcium carbonate (CaCO3) controlled by Pluronic P123 in a room-temperature ionic liquid, ethylamine nitrate (EAN), was investigated. The CaCO3 aggregates were obtained by rapid mixing of ammonium carbonate ((NH4)2CO3) and calcium chloride (CaCl2). Cubic calcite, spherical vaterite, and bagel-like vaterite were obtained easily by changing P123 concentration and reaction temperature. The morphologies of the as-prepared CaCO3 aggregates were investigated by transmission electron microscopy and scanning electronic microscopy. The phase change of the obtained crystals was confirmed by X-ray diffraction and Fourier transform infrared spectroscopy. It was shown that higher P123 concentration and higher reaction temperature favor the formation of vaterite in EAN. Unusual bagel-like vaterite was first obtained at 60 °C in the presence of 5 g/L P123 in EAN. Mineralization of CaCO3 regulated by P123 in EAN is a simple, novel, and environment-friendly strategy for vaterite synthesis.

The physicochemical properties of the mixed zwitterionic surface activity ionic liquid/anionic surfactant (N-alkyl-N′-carboxymethyl imidazolium inner salts/sodium dodecyl sulfate, [N-C12, N′-CO2-Im]/SDS) at various molar ratios (R1 = C[N-C12,N′-CO2-Im]/(C[N-C12,N′-CO2-Im] + CSDS) were investigated by surface tension and steady-state fluorescence measurements. The results show that the mixed [N-C12, N′-CO2-Im]/SDS system has a much lower cmc value and higher surface activity than individual surfactant. Compared with the mixed zwitterionic betaine surfactant/SDS system, the mixture studied exhibits a stronger synergism, i.e., more negative interaction parameters (βm and βσ). Through addition of NaCl, the wormlike micelles (WMs) could be formed in a [N–C12, N′-CO2-Im]/SDS system. Steady and dynamic rheology was employed to characterize the WMs with different surfactant ratio (R1), NaCl concentration, and temperature. An optimal composition, viz., CT = 60 mM, R1 = 0.45, and CNaCl = 0.10 M, was detected to form the strongest and longest wormlike micelles. Compared with the WMs formed by a traditional zwitterionic C12 betaine/anionic surfactant mixture (e.g., laurylamidopropyl betaine/SDS), the WMs studied have a stronger network structure, which is expected to have potential applications in some fields, such as in nanomaterials synthesis, personal care products, and flooding liquid for tertiary oil recovery.

Nonionic pluronic amphiphilic triblock copolymer F68 was employed to control the growth of calcium carbonate in a biomineralization process. The effects of the concentrations of F68, Ca2+ and CO32−, pH values and temperatures were investigated systematically. The as-obtained CaCO3 particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. Calcium carbonate with various morphologies including stacked rhombohedral, spherical, grass-shaped, flower-shaped, etc. was prepared under different experimental conditions. The rod-like and core-shell structures of calcite crystals were obtained for the first time by varying the concentration of F68 and pH value in the aqueous solutions. Based on the results, possible mechanisms were proposed. The ionization product (Qi) of Ca2+ and OH− was first used to explain the formation mechanism of CaCO3 crystals at different initial pH conditions.Highlights► Core-shell structures of calcite crystals are obtained. ► Rod-like calcites are synthesized. ► The ionization product is used to explain the formation mechanism.

Multi-walled carbon nanotubes (MWCNTs) could be well dispersed in the aqueous solution of 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br), an amphiphilic ionic liquid, because of hydrophobic interaction. [C16mim]Br could self-assemble and form hemimicelles on the surfaces of MWCNTs. MWCNTs became positively charged due to the adsorption of C16mim+ and negatively charged Au nanoparticles (Au NPs) could be easily attached to the surfaces of MWCNTs by electrostatic interaction. In the UV–vis region, disappearance of characteristic adsorption peaks of MWCNTs and Au NPs indicates that Au NPs are completely attached to the MWCNTs in aqueous solution. Transmission electron microscope (TEM) images show Au NPs are uniformly deposited on the walls of MWCNTs. Both X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) patterns illustrate the existence of high purity Au NPs in MWCNTs–Au NPs hybrids. In this work, amphiphilic ionic liquid has been used to disperse MWCNTs and subsequently MWCNTs–Au NPs hybrids have been prepared by a very simple strategy.Graphical abstractMulti-walled carbon nanotubes (MWCNTs) were well dispersed in the aqueous solution of 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br) firstly. MWCNTs became positive charged due to the adsorption of C16mim+ and negative charged Au nanoparticles (Au NPs) could be easily attached to the surfaces of MWCNTs by electrostatic interaction. UV–vis and transmission electron microscope (TEM) both indicate that Au NPs are completely attached to the MWCNTs in aqueous solution. X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) patterns illustrate the existence of high purity Au NPs in MWCNTs–Au hybrids.Highlights► A novel and easy method has been developed to decorate MWCNTs with Au NPs. ► C16mimBr was used to prepare CNTs and metal nanoparticles hybrid. ► MWCNTs became positively charged after the adsorption of C16mim+. ► Negatively charged Au nanopaticle was easily attached to CNTs by electrostatic effect.

Halogen-free, low-cost alkyl sulfate-based surface active ionic liquids (SAILs), 1-butyl-3-methylimidazolium dodecyl sulfate ([C4mim][C12SO4]), and N-butyl-N-methylpyrrolidinium dodecyl sulfate ([C4MP][C12SO4]) were easily synthesized through ion exchange reaction. The aggregation behaviors of [C4mim][C12SO4] and [C4MP][C12SO4] in aqueous solution were investigated by surface tension, electric conductivity, and static fluorescence quenching. Both [C4mim][C12SO4] and [C4MP][C12SO4] have rather lower cmc, γcmc values and higher pC20, πcmc values than those reported for the traditional ionic surfactant, sodium dodecyl sulfate (SDS), and imidazolium-based SAIL, 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br), with the same hydrocarbon chain length. The thermodynamic parameters evaluated from electric conductivity measurements show that the micelle formation of [C4mim][C12SO4] and [C4MP][C12SO4] is entropy-driven in the temperature range investigated. Lower average aggregation number indicates that the micelles of two SAILs present much looser structure. It is found that both the nature and the ring type of counterions can affect the aggregation behavior in aqueous solution. 1H NMR results of [C4mim][C12SO4] were used to further verify the mechanism of micelle formation. Hydration ability and steric hindrance of the imidazolium or pyrrolidinium counterion as well as the cooperative hydrophobic interaction of longer alkyl chain of [C12SO4] anion and comparatively shorter alkyl chain of [C4mim] or [C4MP] cation are proposed to play critical roles in the aggregation of [C4mim][C12SO4] and [C4MP][C12SO4].

Ester-functionalized anionic surface-active ionic liquids (SAILs), 3-methyl-1-(ethoxycarbonylmethyl)imidazolium dodecylsulfate ([C1COOC2C1im][C12SO4]) and 3-methyl-1-(ethoxycarbonylmethyl)pyrrolidinium dodecylsulfate ([C1COOC2C1Py][C12SO4]), were synthesized. The tensiometric profiles demonstrate that, in pure water, the studied SAILs exhibit higher surface activity than the traditional anionic surfactant, sodium dodecyl sulfate (SDS), and cationic SAILs, 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br) and N-dodecyl-N-methylpyrrolidimium bromide (C12MPB), with the same hydrocarbon chain length. The interaction between bovine serum albumin (BSA) and the anionic SAILs in pH 7.4 buffer solution was systematically investigated by various techniques. The results show that the cationic ring has a slight effect on the BSA–SAIL interaction. The binding isotherms of BSA with the SAILs display four characteristic regions with increasing SAIL concentration. The unfolding of BSA occurs in the third region. Fluorescence spectroscopy indicates that the studied SAILs cause the exposure of tryptophan residues to a hydrophobic environment, and [C1COOC2C1im][C12SO4] can more effectively reduce the fluorescence intensity of BSA at low SAIL concentrations than [C1COOC2C1Py][C12SO4]. Circular dichroism spectroscopy evidences that the denaturation extent of BSA induced by [C1COOC2C1im][C12SO4] is higher than that of [C1COOC2C1Py][C12SO4].

Interactions between various modified semiconductor nanocrystal, cadmium sulfide quantum dots (CdS QDs) and bovine serum albumin (BSA) and lysozyme (LZY) were investigated. CdS QDs capped with mercaptoethanol (MPA), l-cysteine (Lcys) and glutathione (GSH) were synthesized in aqueous solution and characterized by UV–vis and fluorescence spectrum. Circular dichroism (CD) and fluorescence spectrum were used to detect the interactions between as-prepared CdS QDs and protein molecules. The interaction parameters, including binding constant (Kb), binding site number (n) and quench constant (Kq), were determined by fluorescence spectrum. The changes of secondary structures of the proteins were detected by CD. The results imply that CdS QDs modified by different agents have dramatically different binding strength with protein molecules. The results obtained here analyze the biosafety of CdS QDs in terms of the biological behavior of biomolecules and could serve as basis for the application of CdS QDs to bioscience.Graphical abstractInteractions between three different capped (MPA, GSH, Lcys) CdS QDs and two proteins (BSA and LZY) were investigated by fluorescence spectrum and circular dichroism (CD).Highlights► Interactions between three modified CdS QDs and two proteins were investigated. ► MPA, GSH and Lcys capped CdS QDs showed different affinity to proteins. ► GSH capped CdS QDs showed weakest quenching effects. ► All three CdS QDs could change the microenvironment of Tyr residues in proteins. ► Second structures of proteins changed differently with addition of three CdS QDs.

Butyl-α,β-bis(dodecylimidazolium bromide) ([C12-C4-C12im]Br2) is a new type ionic liquid-based Gemini surfactant. Multiwalled carbon nanotubes (MWCNTs) can be dispersed effectively in [Cn-C4-Cnim]Br2 aqueous solutions due to its special molecular structure, including two imidazole ring head groups and two hydrophobic chains. The resulted MWCNT suspensions are stable for more than one month and no precipitation is observed. Both UV-vis-NIR and transmission electron microscopy (TEM) studies indicate that the MWCNTs dispersed in solutions are present as individual. The dispersed amount of MWCNTs first increased and then decreased with increasing the concentration of [C12-C4-C12im]Br2. Compared with single-chain ionic liquid-based surfactant 1-butyl-3-alkylimidazolium bromide ([Cnmim]Br), [Cn-C4-Cnim]Br2 has stronger ability of dispersing CNTs, which is also ascribed to its molecular structure. It was also found that the [Cn-C4-Cnim]Br2 with a longer hydrocarbon chain demonstrated a stronger dispersion ability. The ζ-potential measurements show that the MWCNTs dispersed in [C12-C4-C12im]Br2 aqueous solution have relatively high positive charges, which can conclude that it is the Coulomb force between CNTs that makes them stable. Based on these, the possible dispersion mechanism has been proposed.

Self-association of three long-chain imidazolium ionic liquids (ILs), [C12mim]Br, [C14mim]Br, and [C16mim]Br, in aqueous solution was studied by surface tension measurements over a temperature range from (278.15 to 328.15) K. Effects of temperature and hydrocarbon chain length of the three long-chain ILs on the critical micelle concentration (CMC) were examined. Thermodynamic parameters, ΔmicG, ΔmicH, and ΔmicS, of micellization were determined by applying a mass-action model equation. Isothermal titration microcalorimetry was used to obtain the enthalpy change upon micellization of the three long-chain ILs at 298.15 K. Moreover, the CMCs and the thermodynamic parameters (ΔmicG, ΔmicH, and ΔmicS) were determined based on the isothermal titration microcalorimetry results. These CMC values are approximately equal to the CMCs obtained by surface tension measurement.

Wormlike micelles, obtained in anionic surfactant sodium oleate (NaOA) solutions in the presence of sodium phosphate (Na3PO4), were studied using the steady and dynamic rheological methods. The laboratory simulation flooding experiments were used to investigate the effects of flooding for the wormlike micelles system. The results show that the oil recovery is 32.7%. This flooding system is a new type and has high activity with a low cost.

The enthalpies of mixing of l-serine and l-threonine with butanol and their respective enthalpies of dilution in aqueous solutions at 298.15 K and those of amino acids (glycine, l-alanine, l-serine, l-threonine, and l-proline) with butanol in aqueous solutions at 310.15 K were determined as a function of the mole fraction by flow microcalorimetric measurements. These experimental results have been analyzed to obtain the heterotactic enthalpic interaction coefficients (hxy) according to the McMillan−Mayer theory. The results obtained in the present work are compared with the data of our previous work at 298.15 K. It has been found that the hxy coefficients between the amino acid molecules studied and butanol molecules in aqueous solutions at (298.15 and 310.15) K are all positive. The hxy coefficients at 310.15 K are more positive than those of 298.15 K for the same system studied. The results are discussed in terms of solute−solute interaction and solute−solvent interaction.

The interactions between a surface active imidazolium ionic liquid (IL), 1-tetradecyl-3-methylimidazolium bromide (C14mimBr) and bovine serum albumin (BSA) were studied. To investigate the structure changes of BSA induced by addition of C14mimBr, this system was studied by surface tension, isothermal titration microcalorimetry, far-UV circular dichroism (CD) and fluorescence spectra. The surface tension measurement shows the formation of C14mimBr/BSA complex and the effect of the complex on surface tension. Furthermore, it reveals the interaction type. The enthalpy change in the whole interaction process between C14mimBr and BSA was obtained by isothermal titration microcalorimetry, and the results prove the alteration of the BSA structure. To realize the structure alteration position more definitely, far-UV CD was used to obtain the contents of α-helix and random coil. Changes of these contents reveal that the secondary structure of BSA changes with addition of C14mimBr. Fluorescence spectra are used to prove that the alteration of the secondary structure is due to the interactions of C14mimBr molecules and amino acid residues. They show that tryptophan (Trp) residues, one of the intrinsic fluorophores in BSA, are exposed to a hydrophobic microenvironment with the addition of C14mimBr.

The enthalpies of mixing of six kinds of aqueous amino acid solutions (glycine, l-alanine, l-valine, l-serine, l-threonine and l-proline) and aqueous 1,2-ethanediol solution and their respective enthalpies of dilution have been measured at 298.15 K using flow microcalorimetry. The experimental data have been analyzed in terms of the McMillan–Mayer formalism to obtain the heterotactic enthalpic interaction coefficients. The heterotactic enthalpic pairwise interaction coefficients, hxy, have been discussed from the points of view of solute–solute interactions.

The enthalpies of mixing of glycine, l-α-alanine, l-γ-aminobutyric acid, l-α-valine, l-α-serine and l-α-threonine with cyclohexanone in aqueous solutions and their respective enthalpies of dilution have been measured by calorimetry at 298.15 K. Experimental enthalpies of dilution and mixing have been correlated with the virial expansion equation that was obtained with the McMillan–Mayer theory. The enthalpic interaction parameters hxy, hxxy and hxyy of the amino acids studied with cyclohexanone in aqueous solutions have been evaluated, and the heterotactic enthalpic pair interaction coefficients (hxy) are discussed in terms of solute–solute interactions.

Mixing enthalpies of aqueous l-serine and l-threonine solutions and aqueous tetrohydrofuran (THF) and 1,4-dioxane solutions and their dilution enthalpies have been determined with a Thermometric-2277 Thermal Activity Monitor at T=298.15 K. The hxy values, obtained with the McMillan–Mayer formalism, for the α-amino acids bearing polar side-chain (l-serine and l-threonine) with THF and 1,4-dioxane are compared with values reported in the literature for the α-amino acids with non-polar side-group (glycine, l-alanine, l-aminobutyric acid and l-valine) with THF and 1,4-dioxane. The results are interpreted in terms of solute–solute interactions. The group additivity concept by Savage and Wood (SWAG) has also been used. Contributions of each amino acid, functional group have been estimated.

Nano- and micro-sized calcium carbonate (CaCO3) with various morphologies including multi-petal-flower-shaped, multi-step-cube-shaped, coral-shaped, dendrite-shaped and multi-antenna-shaped was successfully prepared using dodecyltrimethylammonium bromide (DTAB) micellar vevulsant. The effects of temperature, pH and the concentration of DTAB micellar solution on the morphology and crystalline form of CaCO3 were systematically investigated. The prepared CaCO3 was characterized by Scanning Electron Microscope (SEM), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR). The concentration of DTAB micelle, pH and reaction temperature are found to play crucial roles in the morphology, size and crystalline form of the final products. On the base of the characterizations, a possible self-assembled mechanism was proposed. The novel multi-petal-flower-shaped and multi-antenna-shaped CaCO3 may have some unique properties and potential applications in the future.

Cationic surfactants, didodecyldimethylammonium bromide (DDAB), 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br) and DDAB/[C12mim]Br mixture were used to induce the formation of calcium carbonate (CaCO3) crystals at ambient temperature. The obtained CaCO3 particles were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The morphologies of CaCO3 crystals changed from laminated cube to sphericity and string shape with the increase of DDAB and [C12mim]Br concentration, respectively. Flower-shaped CaCO3 crystals were synthesized in the mixed DDAB/[C12mim]Br system. More importantly, it was found that the complete conversion from calcite to vaterite was achieved at room temperature only through changing DDAB concentration. The regulations of DDAB and [C12mim]Br to CaCO3 crystals have been compared with that of dodecyltrimethylammonium bromide (DTAB) in our previous work and possible mechanisms have been proposed. It is shown that the cationic surfactants can control the crystallization of CaCO3 and the number of hydrophobic alkyl chains of cationic surfactants might be more effective in modulating the crystallization of vaterite than the head groups.Highlights► Cationic surfactants are used to induce CaCO3 crystals. ► Various CaCO3 morphologies are synthesized. ► Conversion from calcite to vaterite is achieved by controlling DDAB concentration.

The ionic liquid (IL), tetrabutylphosphonium trifluoroacetate ([P4444][CF3COO]), showed a low critical solution temperature (LCST)-type phase transition in water. Using this temperature-sensitive IL and the Triton X-100/H2O system, the reversible transformation between micelles and microemulsions was thus realized by a thermal stimulus for the first time.