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The effect of spacer lengths of imidazolium gemini surfactant [C14-n-C14im]Br2 (n = 2, 4, 6) on the equilibrium, thermodynamics and kinetics of Au(III) extraction from hydrochloric acid medium were investigated in this article. The thermodynamic parameters, including the changes in enthalpy (ΔH*), entropy (ΔS*) and Gibbs free energy (ΔG*) were determined. The values of ΔH* demonstrated that the extraction of Au(III) by [C14-n-C14im]Br2 was endothermic at first and exothermic at last. The kinetics study found that extraction rate became faster when the spacer lengths were increased. Moreover, kinetics results demonstrated that the diffusion is the controlling step, and the mass transfer coefficients of Au(III) in the investigated systems indicated that the resistance of mass transfer was smaller when the spacer lengths was longer. The studies of interfacial tension further confirmed the better extractability of [C14-n-C14im]Br2 with longer spacer lengths. Our results reveal efficient and sustainable gold separation. [ABSTRACT FROM AUTHOR]

Thermal- and ultrasound-triggered organogels formed by an imidazolium-based salt-free catanionic surfactant 1-tetradecyl-3-methylimidazolium methyl orange [Cmim][MO] in dimethyl formamide (DMF) were investigated. The [Cmim][MO] organogels exhibited luminescent property owing to the aggregation-induced emission (AIE) by noncovalent interaction and displayed excellent mechanical strength and reversible sol-gel transition. Furthermore, the self-assembly behavior of [Cmim][MO] in mixed solvents was also investigated. It can be observed that the addition of poor solvents (toluene, HO) in DMF weakened the mechanical strength of the gels. Besides, the fluorescence of gel performs opposite changes towards different kinds of solvent that the addition of solvents without benzene ring structure (ethanol and dichloromethane) reduced the fluorescence while the addition of solvents containing benzene ring structure (xylene, aniline) enhanced the fluorescence greatly owing to the π-π stacking of solvent and MO. These results reveal the important role of heat, ultrasound, and solvents in the formation of the supramolecular organogels and may help us to design new soft materials. [ABSTRACT FROM AUTHOR]

Microemulsions consisting of ionic liquid-type imidazolium gemini surfactants with different spacer lengths ([C14-n-C14im]Br2, n = 2, 4, 6), cyclohexane, n-hexyl alcohol and hydrochloric acid solution, were investigated for Au(iii) extraction. [C14-n-C14im]Br2 in the microemulsion played a dual role as surfactant and extractant. The extraction efficiency (E%) of the [C14-n-C14im]Br2/cyclohexane/n-hexyl alcohol/HCl microemulsion system for Au was above 99% under optimal conditions. The results of our study indicated that the Au(iii) extraction ability of the three different [C14-n-C14im]Br2 with different spacer lengths was better with longer a spacer. The mechanism for the Au(iii) extraction by [C14-n-C14im]Br2 was confirmed to be based on an anion-exchange process by the continuous variation method and spectroscopic analysis (UV-Vis, FT-IR, 1H-NMR). The FT-IR spectra indicated that the better extraction ability of [C14-n-C14im]Br2 for Au(iii) was positively correlated with the spacer length, due to a less significant steric effect of the methylene groups in surfactants with longer spacers. The electric conductivity values of the [C14-n-C14im]Br2 microemulsions indicated that surfactants with longer spacers can ionize to a higher extent to give more [C14-n-C14im]2+ cations and Br− anions, thus promoting anion-exchange and further increasing E%. [ABSTRACT FROM AUTHOR]

The effects of alkaline amino acids l -Lysine ( l -Lys) and l -Arginine ( l -Arg) on the lyotropic liquid crystal (LLC) behavior of ionic liquid-type imidazolium surfactant (1-tetradecyl-3-methylimidazolium bromide, C 14 mimBr) were investigated systematically. The corresponding properties were investigated by polarized optical microscopy (POM), small angle X-ray scattering (SAXS), field emission-scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy and rheological measurements. The results indicated that with the introduction of l -Lys, LLC phase of C 14 mimBr gradually undergoes the transition to an isotropic homogeneous phase, which demonstrated to be worm-like micelles (WLMs). While for C 14 mimBr/ l -Arg system, it remained the hexagonal phases and merely induced the variation of the mechanical strength of C 14 mimBr LLCs. It can be speculated that the balance between electrostatic interaction, H-bond interaction, and hydrophobic interaction plays an important role in the phase transition of C 14 mimBr/amino acids. Our work can contribute to a better understanding of the effect of the additions especially amino acids on the influence of the surfactant aggregates and their macroscopic properties, which maybe open the door for wide applications in the biological system. [ABSTRACT FROM AUTHOR]

Silicone surfactants favor spreading at interfaces and siloxane has strong interaction with carbon nanotubes (CNT), thus silicone surfactant may be a good dispersant of CNT. Here, four silicone surfactants (named S1E19, S2E38, S2E16 and S1E16P8) were used to disperse CNT in aqueous solutions. The effects of surfactant structure and concentration on the ability at dispersing CNT were considered. All of the four silicone surfactants can disperse CNT in aqueous solution and the sample with 1,000 mg L S1E16P8 was the best one. The hydrophilic group polyoxyethylene (PEO) and the hydrophobic groups siloxane and polypropylene (PPO) are crucial factors in the ability of dispersing CNT. S2E38 with more ethylene oxide (EO) groups has a stronger ability to disperse CNT than S2E16. The dispersion system provided by S1E19 which contains fewer siloxane and EO groups is relatively unstable and disperses less CNT. These experimental results are explained by molecular dynamics simulation. S2E38 compared with S1E19 and S2E16 has stronger interactions with CNT. The interaction energy of CNT with S1E16P8 which has a PPO moiety but fewer siloxane groups is close to that of S2E16. Furthermore, it can be concluded that these four surfactants are adsorbed on CNT mainly by van der Waals forces and the Si-O-Si chain of silicon surfactant was flexible due to the long Si-C bond and it could easily wrap onto the surface of CNT through hydrophobic and other intermolecular interactions. The hydrophilic part of PEO helped the CNT dispersed in the aqueous solution and prevented CNT from aggregating in water through steric stabilization. [ABSTRACT FROM AUTHOR]

Highlights: [•] The reverse vesicles in toluene are smaller compared to those in cyclohexane. [•] The molecular bilayers have a compact organization and are highly curved. [•] Small vesicles can fuse to form bigger ones with time. [•] At elevated temperatures, the vesicles became “soft” before clearance. [•] Cryo-TEM was used for the first time to detect reverse vesicles in toluene. [ABSTRACT FROM AUTHOR]

A water-in-oil microemulsion was prepared by using nonionic surfactant Triton X-100, 1-hexanol, cyclohexane and AgNO3 aqueous solution with a concentration of 0.2 mol L−1. Successive addition of sodium borohydride (NaBH4), ammonium hydroxide (NH3·H2O) and tetraethyl orthosilicate (TEOS) to this microemulsion leads to the formation of hierarchically-organized Ag@SiO2 hybrid nanoparticles with Ag nanocrystals randomly distributed inside amorphous SiO2, as proved by transmission electron microscopy (TEM) and high-resolution electron microscopy (HRTEM) observations. In many cases, H2 gas bubbles, which were produced during the reduction of Ag+, were found to influence the structures of Ag nanocrystals. The morphologies of the hybrid nanoparticles and the H2-induced cavities can be easily tuned by the molar ratio of AgNO3 to NaBH4 and the volume ratio of AgNO3 aqueous solution to TEOS. Embedded in amorphous SiO2, the Ag nanoparticles are highly stable, while the unprotected Ag nanocrystals underwent fast aggregation. The inner Ag nanocrystals have dominant (111) planes and are optically active, as shown by X-ray powder diffraction (XRD) and UV-vis measurement, respectively. These properties make these Ag@SiO2 hybrid nanoparticles fascinating candidates for a variety of applications in catalysis and life science. [ABSTRACT FROM AUTHOR]

Abstract: A carbon nanotube/inorganic hybrid material has been fabricated by coupling Eu(III) complexes onto multi-walled carbon nanotubes (MWCNTs). Successful coupling has been verified by X-ray photoelectron spectroscopy (XPS) measurement where a clear signal from Eu3d has been identified. When sonicated in hexaethylene glycol monododecyl ether (C12E6) or sodium dodecyl sulfate (SDS) aqueous solutions, the MWCNTs with Eu-complex attached (denoted as Eu-MWCNTs hereafter) can be dispersed. UV–vis measurements on a dilute dispersion of Eu-MWCNTs in SDS aqueous solution reveal the characteristic absorption from Eu(III) complexes, which gives further proof of the successful coupling. The strong luminescent properties of Eu-MWCNTs allow them to be observed directly under a fluorescence microscope. Interestingly, it is found that Eu-MWCNTs can undergo continuous movements in C12E6 or SDS dilute solutions. When Eu-MWCNTs are incorporated into the lyotropic liquid crystal phase formed by C12E6 (above 40% by weight), however, movements have been hindered. Small angle X-ray scattering measurements showed that Eu-MWCNTs are ordered in the lyotropic liquid crystal. Fluorescence microscopy observations reveal that the luminescent properties of the Eu-MWCNTs have not been affected by the liquid crystalline surfactant matrix. [Copyright &y& Elsevier]

The surface dilational modulus of the star-like block copolymer AP432 and linear block copolymer L64 was studied using the oscillating bubble method at an accessible frequency range of 0.05 to 2 Hz, which was compared with anionic surfactant sodium oleate (C17H33COONa) and the influence of inorganic salt NaNO3 on the surface dilational modulus of AP432 and L64 was also studied. The results indicate that for AP432 and L64 the dilational modulus varies slightly, just decrease gradually with concentrations increasing and never reaches high values with the dilational frequency increasing, but the dilational modulus of C17H33COONa increases gradually with the increase of dilational frequency and pass through the maximum values with increasing concentration. The properties of AP432, L64, and C17H33COONa at the air/water interface were also observed by surface tension measurement. Based on these experimental results, a simple possible adsorption model of these molecules at air/water interface is proposed. [ABSTRACT FROM AUTHOR]

Abstract: The interaction between a star-like block copolymer (AP432) and an anionic surfactant sodium oleate (C17H33COONa) was investigated in detail both at the air/water interface and in bulk aqueous solutions. The results of surface tension show that AP432 and C17H33COONa could form mixed micelles. The results obtained from the oscillating barrier measurements at low dilational frequencies (0.01–0.1Hz) reveal that the maximum values of the dilational modulus for AP432/C17H33COONa mixed system moved to lower concentrations compared to those of single AP432 or C17H33COONa aqueous solutions. Steady-state fluorescence measurements indicate that after mixing, the I 1/I 3 values of AP432/C17H33COONa system above the cmc are higher than those of single AP432 or C17H33COONa solutions. This is probably due to a looser pack of the molecules within micelles for the AP432/C17H33COONa mixture, which is also consistent with the results obtained from TEM observations. For comparison, the interaction between a commercially available linear PEO–PPO–PEO copolymer (Pluronics L64) and C17H33COONa was also studied. All experimental results give clear evidence that the interaction between L64 and C17H33COONa is different from that between AP432 and C17H33COONa. [Copyright &y& Elsevier]

The adsorption kinetics of the double‐chain surfactant AOT and NaDEHP are comparatively investigated by dynamic surface tension (DST) measurements. The parameters n and t* representing the diffusion speed of the surfactant molecules from bulky solution to the sublayer and from the sublayer to the surface are obtained according to the equation proposed by Rosen. The results show that the values of n and t* both decrease with the increase of the surfactant concentrations. While the n value of the AOT system is smaller than that of NaDEHP and the t* is the inverse, indicating the faster diffusion of AOT molecules and the larger adsorption potential for NaDEHP molecules. The effect of the salt on the dynamic adsorption course is also studied. The results show that the decreasing rate of the DST for the two surfactants both increase with the rise of NaCl concentration; however, the effect of NaCl on AOT is stronger than that on the NaDEHP system. This result is in agreement with the equilibrium surface tension result. [ABSTRACT FROM AUTHOR]

General empirical relationships have been developed for estimating the Krafft point of anionic surfactants and cloud point of nonionic surfactants using the quantitative structure‐property relationship (QSPR) method. For the Krafft point, a six‐parameter structure‐property relationship (R 2 =0.941) was obtained for a diverse set of 46 anionic hydrocarbon surfactants and a three‐parameter relationship (R 2 =0.864) for 19 linear fluorocarbon anionic surfactants by employing topological, thermodynamic, and structural descriptors. For the cloud point of 64 nonionic surfactants with six representative structures, the best multiple linear regression model involved five parameters and had a correlation coefficient of R 2 =0.921. From these relations Krafft point or cloud point of surfactants can be estimated based on their molecular structure. [ABSTRACT FROM AUTHOR]

Two-component hydrogels were formed by the supramolecular assembly of β-cyclodextrin (β-CD) and ionic liquid-type imidazolium gemini surfactants ([C 14 -4-C 14 im]Br 2 ) in water. The mechanism for the formation of hydrogels was studied by various methods including transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and rheological measurements. It can be revealed that in these hydrogels, β-CD is as the host and [C 14 -4-C 14 im]Br 2 is as the guest and they can form inclusion complexes. Moreover, the properties of the hydrogels of β-CD/[C 14 -4-C 14 im]Br 2 are responsive to external stimuli and can be controlled by changing the host/guest ratio or the temperature. For example, by increasing the temperature, the hydrogels change into solutions and this process is reversible and reproducible. Taken together and according to the previous study, it is suggested that the main driving forces are hydrogen bonding between β-CDs, β-CD and the imidazolium headgroup of [C 14 -4-C 14 im] 2+ , β-CD and the solvent, and the hydrophobic interaction between the hydrophobic chains of [C 14 -4-C 14 im]Br 2 . The properties of these hydrogels led them be useful in the field of biomedical applications such as injectable drug delivery systems. [ABSTRACT FROM AUTHOR]

A salt-free surfactant system formed by a peptide amphiphile with short headgroup (PA, C 16 -GK-3) and a zwitterionic surfactant (dodecyldimethylamine oxide, C 12 DMAO) in water has been systematically investigated. The microstructures and properties of C 16 -GK-3/C 12 DMAO mixed system were characterized using a combination of microscopic, scattering and spectroscopic techniques, including transmission electron microscopy (TEM), field emission-scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Fourier transform infrared (FT-IR), circular dichroism (CD) and rheological measurements. Rich phase transitions have been observed by adjusting the concentration of C 16 -GK-3. Investigation of the hydrogels of C 16 -GK-3/C 12 DMAO with TEM, SEM and AFM showed that all of these hydrogels form nanobelts. The nanobelt formation is performed in a hierarchical manner: β -sheet peptides and C 12 DMAO first interact each other to form small aggregates, which then arrange themselves to form one dimensional (1D) left-handed ribbons. The ribbons further aggregated into flat and rigid nanobelts. We proposed a mechanism to interpret the self-assembly process according to the specific peptide structure as well as multiple equilibria between the hydrogen bonding interactions between the headgroups of C 16 -GK-3, between C 12 DMAO molecules and the headgroups of C 16 -GK-3, chirality of the amino acid residues and hydrophobic interactions of the alkyl chains. [ABSTRACT FROM AUTHOR]

Abstract: The interaction between 4-chloro-(2′-hydroxylphenylazo)rhodanine (ClHPAR) and cationic surfactant cetyltrimethyl ammonium bromide (CTAB) was investigated by surface tension, absorption spectra, resonance light scattering (RLS) spectra and transmission electron microscopy. It can be concluded from the experimental results that the hydrophobic forces cannot be neglected, even though the electrostatic interaction between ClHPAR and CTAB plays an important role. The RLS spectral behavior of ClHPAR changes in the presence of CTAB. The efficiency and the effectiveness of ClHPAR–CTAB mixture to decrease the surface tension of water are higher than those of any single component, i.e. CTAB and ClHPAR. As one might expect, NaCl and urine have different effects on the interaction between ClHPAR and CTAB and their interaction also depends on pH. [Copyright &y& Elsevier]

In this paper, in order to successfully achieve a fluorescent polyoxometalate (POM) probe with high luminescence, aggregation enhanced emission of POM is achieved by a self-assembly strategy. In detail, Eu-polyoxometalate (Na 9 [EuW 10 O 36 ]·32H 2 O (EuW 10)) and ionic-liquid-type imidazolium gemini surfactants ([C 14 -n-C 14 im]Br 2 , n = 2, 4, 6) constructed a vesicle with aggregation enhanced emission phenomenon. With the introduction of [C 14 -n-C 14 im]Br 2 , the luminescence intensity increased sharply and compared the effect of the different space length of [C 14 -n-C 14 im]Br 2 , the introduction of [C 14 -2-C 14 im]Br 2 had the best luminescence effect and the strongest luminescence of EuW 10 /[C 14 -2-C 14 im]Br 2 was 32 times that of pure EuW 10. Thus, a sensitive selective off-luminescence chemical sensor EuW 10 /[C 14 -2-C 14 im]Br 2 was developed for the label-free detection of Cr3+ and MnO 4 − in aqueous solution with lower detection limits of 0.926 μM and 1.70 μM, respectively. Collision between the fluorophore and Cr3+ or MnO 4 − caused dynamic quenching. Luminescence quenching of Cr3+ was attributed to Förster resonance energy transfer (FRET) while luminescence quenching of MnO 4 − was attributed to UV–vis competitive absorption. Our strategy for combining polyoxometalates with surfactants to construct aggregation enhanced emission systems is expected to provide new ways to develop simple, economical, fast and sensitive sensors in environmental applications such as metal ion detection. [ABSTRACT FROM AUTHOR]

Abstract In this article, ionic liquid-type imidazole gemini surfactants with different spacer length ([C 14 -n-C 14 im]Br 2 , n = 2, 4, 6) were synthesized and 3D nanostructures were constructed by using a novel Preyssler-type POM (K 12.5 Na 1.5 [NaP 5 W 30 O 110 ]∙15H 2 O, abbreviated as P 5 W 30) and [C 14 -n-C 14 im]Br 2 through the ionic self-assembly (ISA) strategy. Hybrid nanostructures were fully characterized by various characterization methods, such as transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray small-angle scattering, X-ray diffraction (XRD), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). By changing the spacer length of [C 14 -n-C 14 im]Br 2 , the rigidity and space volume of the gemini surfactants can change, which can affect the behavior of [C 14 -n-C 14 im]Br 2 /P 5 W 30 , such as the size of the nanostructures, the behavior of thermotropic liquid crystals, d spacing of SAXS, spatial displacement and decomposition temperature. In addition, the calcined [C 14 -6-C 14 im]Br 2 /P 5 W 30 nanostructures exhibit excellent degradation efficiency for methyl orange dyes (MO), which maybe have outstanding application prospects for wastewater treatment. The nanostructure formed by self-assembly not only realizes heterogeneous catalysis, but also solves the problem of water solubility of P 5 W 30 which was easy to recycle. Moreover, the active sites of nanostructures formed by ion self-assembly increase, and the degradation rate was nearly 3 times higher than that of pure P 5 W 30. Our work confirmed that POM and gemini surfactants can construct functional nanostructures through ISA strategy, which can be the perfect candidate for photocatalysis and biomedical. Graphical abstract Scheme. The formation mechanism and morphology evolution of [C 14 -n-C 14 im]Br 2 /P 5 W 30 nanospheres. Unlabelled Image Highlights • The ionic self-assembly of gemini surfactants and POM was studied. • The obtained nanosphere structure has good degradation dye properties. • The synthesized gemini surfactants has very good thermotropic liquid crystal behavior. • This system may open the way for the catalyst design of photocatalytic degradation in environmental applications. [ABSTRACT FROM AUTHOR]

Supramolecular hydrogels were facilitated by α-cyclodextrin (α-CD) and three silicone surfactants named S1E8, S1E19 and S2E38, respectively. Influences of the molecular structure and concentration of the silicone surfactants on the formation of hydrogels and their stabilities were investigated. The hydrogels were characterized by phase behavior study and various techniques. The results indicated that the balance between the hydrophilicity and the hydrophobicity of the silicone surfactants is crucial for the formation and high stability of the hydrogels. S2E38, which has two poly-(ethylene oxide) chains, exhibits a stronger ability to form hydrogels than S1E8 and S1E19 do. Moreover, in vitro study using doxorubicin (DOX) as a model anticancer drug shows that α-CD/silicone surfactant hydrogels can be used as injectable carriers for controlled drug release. [ABSTRACT FROM AUTHOR]

• A novel light-responsive emulsion was prepared by introducing well-defined Cu3. • The emulsification/demulsification of prepared emulsion was achieved through the reversible self-assembly behaviors of Cu3. • The fibers on the interface could be collected and recycled for the new emulsification/demulsification process. An emulsion system with reversible demulsification/emulsification transition triggered by light irradiation was achieved by azo-modified copper nanoclusters Cu 3 (azopz) 3 (Cu3 , Hazopz = (3,5-dimethyl-4-(phenyldiazole)-1H-pyrazole)) in the surfactant (APG0810) oil-in-water emulsion. The phase separation behavior of the emulsion is attributed to the fibrous structures self-assembled from Cu3 in the toluene phase under 365 nm UV irradiation, which break the stability of the emulsion, resulting in the demulsification. Further visible light irradiation and homogenization could recover the emulsion. This process is completely reversible under alternating ultraviolet/visible light treatments. This study shows the first application of metal nanoclusters in controlling demulsification/emulsification by a noninvasive stimulus. Further development of sustainable chemical processes such as catalyst recycling, product separation and hydrogenation reaction is highly expected based on this research. [ABSTRACT FROM AUTHOR]