Gelation behavior and supramolecular chirality of a BTA derivative in a deep eutectic solvent.

As novel solvents, deep eutectic solvents (DESs) are non-toxic, easily producible and biocompatible, which is attractive for eutectogel fabrication. In this work, a benzene 1,3,5-tricarboxamide (BTA) derivative (substituted by three hexanoic acid) was selected to prepare a supramolecular gel in a suitable DES composed of choline chloride and phenylacetic acid molecules. The obtained eutectogel exhibited higher stability than that produced in conventional solvents. The gel microstructure was composed of spiral fiber networks as confirmed from atomic force microscopy and scanning electron microscopy observations. Macroscopic chirality was therefore recognized by the circular dichromatic spectrum, though such a supramolecular chiral signal was random. To explore the gelation mechanism, the effect of BTA derivative molecular structure change was systematically investigated. With the help of Fourier transform infrared spectroscopy and powder X-ray diffraction, the gel formation was attributed to the π-π stacking of adjacent BTA molecules and the three-fold hydrogen bond between amide groups or the hydrogen bond between carboxylic groups. Furthermore, the directional hydrogen bonds between BTA and solvent molecules induced their aggregate to form one-dimensional fibers, which were either left- or right-handed. The obtained results not only extend the gel systems in DESs, but also help design the supramolecular chirality from non-chiral molecules.

Self-assembly of an imidazolium surfactant in aprotic ionic liquids. 2. More than solvents.

As tailorable solvents, the physiochemical properties of ionic liquids can be tuned by the structure of ions. Herein, we investigate the structural effects of ILs on the self-assembly of surfactants. It has been confirmed that the cationic surfactant 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) can self-assemble into micellar and lamellar lyotropic liquid crystal phases in the aprotic ionic liquid (AIL) 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim]BF4). In this work, we explore the aggregation behaviours in AILs with different alkyl chains on the imidazolium group, i.e., 1-propyl-3-methylimidazolium tetrafluoroborate ([Pmim]BF4), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4), 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim]BF4) and 1-octyl-3-methylimidazolium tetrafluoroborate ([Omim]BF4). With the increase of the cation chain length, AILs have better solubility of the solvophobic part of the surfactants and hence a weaker driving force for self-assembly. Therefore, the critical micellization concentration of C16mimBr in AILs increases as confirmed by the surface tension and small angle X-ray scattering characterizations. More interesting things happen to the phase behaviours. Besides the micellar and lamellar lyotropic liquid crystal phases, a hexagonal lyotropic liquid crystal phase is formed in [Pmim]BF4 while hexagonal and bicontinuous cubic lyotropic liquid crystal phases are formed in [Bmim]BF4, [Hmim]BF4 and [Omim]BF4. It is surprising to observe richer phase behaviours in solvents of lower cohesive energy. The detailed structural information of various aggregates has been obtained by small-angle X-ray scattering. It is demonstrated that AILs work as not only solvents but also co-surfactants.

Self-assembled luminescent cholate gels induced by a europium ion in deep eutectic solvents.

Deep eutectic solvents (DESs) with excellent physicochemical properties similar to ionic liquids and biocompatibility are potential solvent candidates for designing novel lanthanide luminescent soft materials. In this paper, the fabrication and characterization of such luminescent gels in three choline chloride (ChCl)-based DESs through self-assembly of the sodium cholate and europium nitrate are presented. The microstructure and gel-like nature of the obtained eutectogels were explored and confirmed by scanning electron microscopy and rheology measurements. While Fourier transform infrared spectroscopy and small-angle X-ray scattering were used to analyze the gel formation mechanism, which was considered to be synergistically driven by metal coordination, hydrogen bonding and solvophobic interactions. All three eutectogels exhibited good photophysical properties. Among these, the one formed in ChCl/urea DES was found to possess the strongest mechanical strength. While the one formed in ChCl/glycerol DES exhibited the longest luminescence lifetime and quantum efficiency. The obtained results demonstrate the possibility of using DESs to construct lanthanide luminescent soft materials or control their properties through the choice of hydrogen-bond donor molecules.

The self-assembly of an imidazolium surfactant in an aprotic ionic liquid. 1. Comparison in aprotic and protic ionic liquids.

The aggregation behaviour of a cationic surfactant in an aprotic ionic liquid has been explored. Prolate micelles are formed at low surfactant concentrations, while a lamellar lyotropic liquid crystal phase is formed at high surfactant concentrations.

Structural Study of Polystyrene-b-poly(acrylic acid) Micelles Complexed with Uranyl: A SAXS Core-Shell Model Analysis.

The interactions between natural colloidal organic matter and actinides in solutions are complex and not fully understood. In this work, a crew-cut polystyrene-b-poly(acry1ic acid) (PS-b-PAA) micelle is proposed as a model particle for humic acid (HA) colloid with the aim to better understand the sequestration, aggregation, and mobility of HA colloids in the presence of uranyl ions. The effects of uranyl ions on the structure of PS29k-b-PAA5k micelles in aqueous solution were mainly investigated by synchrotron small-angle X-ray scattering. A core-shell model, accounting for the thickness and contrast changes of the PAA corona induced by the adsorption of uranyl, was employed to analyze the scattering data. A combination of transmission electron microscopy, dynamic light scattering, and zetametry showed a strong affinity of uranyl ions to PAA segments in water at pH 4-5 that resulted in the shrinkage and improved contrast of the PAA corona, as well as colloidal destabilization at a high uranyl concentration.

Luminescent Sodium Deoxycholate Ionogel Induced by Eu3+ in Ethylammonium Nitrate.

Hydrogels based on bile salts and lanthanide ions have been reported for their easy gelation. However, the weak mechanical properties and water quenching to luminescence of lanthanide ions limit their applications in practice. Hence, a supramolecular ionogel has been prepared here through simply mixing of sodium deoxycholate and europium nitrate in a protic ionic liquid, ethylammonium nitrate (EAN). The prepared ionogel was characterized by scanning electron microscopy, X-ray energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, fluorescence spectroscopy, and rheological measurements. Such an ionogel resulted synergistically from metal coordination and hydrogen bonding. The effect of the solvent structure on gel properties was also explored by comparison with those formed in alkylammonium nitrates with longer chains. EAN was found to behave more effectively both as a solvent and a bridge to enhance the ionogel mechanical strength. The ionogels also exhibited better fluorescent properties than those of the corresponding hydrogels. The obtained results should expand the applications of lanthanide-containing luminescent soft materials in nonaqueous media. It is expected to apply in the fields of solid electrolytes, biosensors, and optics response.

Molecular packing of surface active ionic liquids in a deep eutectic solvent: a small angle X-ray scattering (SAXS) study.

During the past decade, deep eutectic solvents (DESs) have shown promising application in the self-assembly of surfactants. Various aggregates such as micelles, vesicles, lyotropic liquid crystals, microemulsions and gels have been reported. In this research, the phase behaviours of imidazolium surface active ionic liquids (SAILs) CnmimBr (n = 12, 14, 16) were investigated in ChG. With the help of small angle X-ray scattering (SAXS), the types and structure parameters of aggregates were determined. The molecular packing of SAILs was influenced by the solvophobic chain length, surfactant concentration, temperature and solvent, accounting for their different aggregation behaviours. This study would give a good description of the molecular packing of surfactants in DESs.

Investigation of Cu doped flake-NiO as an anode material for lithium ion batteries.

Cu foil is widely used in commercial lithium ion batteries as the current collector of anode materials with excellent conductivity and stability. In this research, commercial Cu foil was chosen as the current collector and substrate for the synthesis of Cu doped flake-NiO via a traditional hydrothermal method. The effect of the ratio of Cu and the calcination temperature on the electrochemical performance of NiO was investigated. The structure and phase composition of the Cu doped flake-NiO electrode were studied through X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and inductive coupled plasma emission spectrometry (ICP). The electrochemical properties of the Cu doped flake-NiO electrode were studied through cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and a galvanostatic charge-discharge cycling technique. According to the results, the Cu-doped NiO electrode, calcined at 400 °C with a molar ratio of Cu : Ni = 1 : 8, exhibited a high reversible charge capacity. The good cycling stability and rate performance indicate that the as-prepared electrode can be applied as a potential anode for lithium ion batteries.

Enhanced full color tunable luminescent lyotropic liquid crystals from P123 and ionic liquid by doping lanthanide complexes and AIEgen.

HYPOTHESIS: The soft materials from ionic liquid mediated lyotropic liquid crystals (LLCs) containing europium complexes have exhibited enhanced luminescence efficiencies and photo-stabilities. The combination with aggregation-induced emissive compounds (AIEgens), however, may produce multicolor and even white emitting LLCs. EXPERIMENTS: Here, we have fabricated highly luminescent hexagonal (H1) LLC containing a red-emitting trisdipicolinate lanthanide complex [choline]3[Eu(DPA)3] (Eu-DPA) from Pluronic 123 and 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF6). Then, a typical AIEgen, tetrakis(4-hydroxyphenyl)ethane (TPE-OH) showing blue light was doped into H1 matrix, accompanying with a green-emitting Tb-DPA. FINDINGS: The emission color of such LLCs could be finely-tuned through changing the molar ratio of Eu-DPA to Tb-DPA. Remarkably, the white emitting H1 LLC with CIE coordinate of (0.328, 0.315) has been prepared by accurately adjusting the relative contents of TPE-OH, Eu-DPA and Tb-DPA. Further, the emission color could be switched between bright white and blue upon tuning UV light from 254 to 365 nm repeatedly. To our best knowledge, such full color tunable luminescent LLCs with improved luminescent performances for both AIEgen and lanthanide complexes have not been reported. This facile approach is universal and various kinds of luminophores can be thus encapsulated into LLC matrices to fabricate soft materials with rich luminescent properties.

Phase behaviours of a cationic surfactant in deep eutectic solvents: from micelles to lyotropic liquid crystals.

In recent years, aggregates formed in deep eutectic solvents (DESs), especially micelles, have attracted much attention. In this study, the phase behaviours of a cationic surfactant, cetylpyridinium bromide (CPBr), in two DESs, choline chloride + glycerol (ChG) and choline chloride + ethylene glycol (ChEG), were investigated in wide concentration and temperature ranges. With the help of small angle X-ray scattering, polarized optical microscopy and rheological measurements, the structures and properties of various aggregates were characterized. The micelles, hexagonal phase, bicontinuous cubic phase and lamellar phase were observed with the increase of CPBr concentration. Such rich phase behaviours were due to the large cohesive energy densities of DESs. Comparative studies in water and ethylammonium nitrate were carried out to explore how well DESs acted as self-assembly media.

(Ce-Al)-oxide pillared bentonite: A high affinity sorbent for plutonium.

The ability of bentonite and montmorillonite pillared by Al-oxide and mixed (Ln-Al)-oxides (Ln = La, Ce) to remove 239plutonium solution species from water is comparatively investigated at pH 7 and pH 4. Small-angle scattering and neutron contrast variation with H2O/D2O mixtures is used to verify the ingress of water in the calcined products after hydrophilicity was introduced by an NH3-H2O vapor treatment. The size and shape of the (La/Ce)-Al oxo-hydroxy pillaring cations (2 nm spheres) is determined by small-angle x-ray scattering from the pillaring solutions. Not all of the oxide pillars improved Pu uptake compared with sodium montmorillonite. At neutral and acidic pH only (Ce-Al)-oxide pillared clays showed the ability to remove Pu over the concentration range studied (1.35 × 10-8-8 × 10-8 mol dm-3) with distribution coefficient (KD) values >104. XPS analysis of the (Ce-Al)-oxide pillared clays indicates the presence of Ce4+ as cerium dioxide. The progressive improvement in sorption performance in the order of pillar type Al2O3 < La2O3-Al2O3 << CeO2-Al2O3 reflects the increasing access of Pu solution species to the clay mineral layers by changes to the basal spacing and specific surface area, and also to the higher stability of the (Ce-Al)-oxide pillars.

Unusual Aggregation Arrangement of Eu-Containing Polyoxometalate Hybrid in a Protic Ionic Liquid with Improved Luminescence Property.

Hybridization of polyoxometalates (POMs) with cationic surfactants offers the opportunity to greatly improve their functionalities as well as processabilities. Here, a surfactant-encapsulated Eu-containing POM complex (SEP) was formed via electrostatic interaction between 1-octadecyl-3-methylimidazolium bromide (OB) and Na9(EuW10O36)·32H2O (EuW10). SEP was first self-assembled in a protic ionic liquid to prepare the soft aggregates to fundamentally avoid the fluorescence quenching by water molecules. The structures and photophysical properties of SEP or aggregates were investigated thoroughly by NMR and FTIR spectroscopy, optical and electron microscopy, small-angle X-ray scattering, and fluorescence measurements. The formed gel-like aggregates were found to compose of three-dimensional networks of microribbons with an interdigitated layered molecular packing of SEP, which was different from the usual inverse bilayer model of POM hybrids in common organic solvents. Compared to EuW10 solid or its aqueous solution, both SEP and its aggregates exhibited intense red luminescence with much improved lifetime and quantum efficiency. In addition, the soft aggregates exhibited an efficient energy transfer and an obviously enhanced monochromaticity, owning to the organized arrangement of EuW10 units and a confined microenvironment to isolate them from each other between adjacent layers. The obtained results will not only present a useful reference to the aggregation behavior of POM hybrids in ionic liquids, but also provide an easy way to design EuW10 luminescent soft materials based on the nonaqueous media.

Visible-light/temperature dual-responsive hydrogel constructed by α-cyclodextrin and an azobenzene linked surfactant.

A novel photo-responsive anionic surfactant with a dimethylamino-substituted azobenzene located at the end of the hydrophobic chain, 6-(4-dimethylaminoazobenzene-4'-oxy)hexanoate sodium (DAH), has been designed. Through the host-guest interaction in aqueous solution, the trans-DAH could be spontaneously included by using two native α-cyclodextrin (α-CD) molecules. The formed hydrophilic inclusion complex (DAH@2α-CD), however, could act as a gelator to induce the formation of a supramolecular hydrogel, which is driven mainly by hydrogen bonds between neighboring α-CDs and also between the carboxylate in DAH and water. Compared with common hydrogels that consist of networks with fibres or discrete polymer chains, the hydrogel formed by DAH@2α-CD was composed of periodic lamellar structures possessing good shear-thinning behavior and much swollen water layers. The more interesting point for such a hydrogel was its visible-light responsibility for gel-sol reversible phase transition. This originated from the introduction of an electron-donating group (dimethylamino) to azobenzene, which noticeably red-shifted the responsive wavelength for its trans-to-cis isomerization. It was also worth noting that the host-guest interaction between azobenzene in DAH and α-CD significantly improved the photo-transition efficiency from trans to cis forms of azobenzene, which played a critical role in the visible-light responsibility of the hydrogel. This unique visible-light-responsive behavior combined with the inherent thermo-responsive property from α-CD should make the prepared hydrogel find more potential applications in biomedical systems.

Effects of a Spacer on the Phase Behavior of Gemini Surfactants in Ethanolammonium Nitrate.

The aggregation behavior of quaternary ammonium gemini surfactants (12-s-12) in a protic ionic liquid, ethanolammonium nitrate (EOAN), was investigated by small-angle X-ray scattering, freeze-fracture transmission electron microscopy, polarized optical microscopy, and rheological measurements. The rarely reported nonaqueous two phases in the ionic liquid were observed at lower 12-s-12 concentrations. The upper phase was composed of micelles, whereas only the surfactant unimers or multimers were detected in the low phase. At higher 12-s-12 concentrations, different aggregates were formed. The lamellar phase was observed in the 12-2-12/EOAN system, whereas the normal hexagonal phases in 12-s-12/EOAN (s = 3, 4, 5, 6, 8) systems and the micellar phase in the 12-10-12/EOAN system were observed. Such a dramatic phase transition induced by the spacer chain length was due to the unique solvent characteristics of EOAN compared to those of water and its counterpart ethylammonium nitrate.

ß-Cyclodextrin induced hierarchical self-assembly of a cationic surfactant bearing an adamantane end group in aqueous solution.

A cationic surfactant with adamantane as the end group, 1-[11-((adamantane-1-carbonyl)oxy)-undecyl]pyridinium bromide (AP), has been synthesized. Its ß-cyclodextrin (ß-CD) induced hierarchical self-assembling behaviors in aqueous solution were investigated using transmission or scanning electron microscopy methods and small-angle X-ray scattering measurements. Like conventional single chain surfactants, micelles could be formed by AP itself in dilute solutions. However, the dramatic phase transitions of these micelles occurred when host-guest inclusions between AP and ß-CD were sequentially produced at different host/guest molar ratios (R), corresponding to the supramolecules with different chemical structures. The AP micelles could be changed into spherical unilamellar vesicles by adding ß-CD to reach an R value of 1 : 1. Such vesicles then evolved into multi-wall nanotubes or hydrogels when the ß-CD amount was further increased to obtain an R value of 2 : 1. The unique structural characteristics of these supramolecular aggregates come from their "monolayer-like" walls, which have rarely been reported in the past for CD/surfactant inclusion complexes. The interesting results obtained here not only enrich the ß-CD/surfactant aggregation systems, but also provide a novel and facile strategy to tune the morphology and structure of aggregates.

Unique Phase Behaviors in the Gemini Surfactant/EAN Binary System: The Role of the Hydroxyl Group.

The hydroxyl group in the spacer of a cationic Gemini surfactant (12-3OH-12) caused dramatic changes of the phase behaviors in a protic ionic liquid (EAN). Here, the effects of the hydroxyl group on micellization and lyotropic liquid crystal formation were investigated through the surface tension, small-angle X-ray scattering, polarized optical microscopy, and rheological measurements. With the hydroxyl group in the spacer, the critical micellization concentration of 12-3OH-12 was found to be lower than that of the homologue without hydroxyl (12-3-12) and the 12-3OH-12 molecules packed more densely at the air/EAN interface. It was then interesting to observe a coexistence of two separated phases at wide concentration and temperature ranges in this 12-3OH-12/EAN system. Such a micellar phase separation was rarely observed in the ionic surfactant binary system. With the increase of surfactant concentration, the reverse hexagonal and bicontinuous cubic phases appeared in sequence, whereas only a reverse hexagonal phase was found in 12-3-12/EAN system. But, the hexagonal phases formed with 12-3OH-12 exhibited lower viscoelasticity and thermostability than those observed in 12-3-12/EAN system. Such unique changes in phase behaviors of 12-3OH-12 were ascribed to their enhanced solvophilic interactions of 12-3OH-12 and relatively weak solvophobic interactions in EAN.

Reverse lyotropic liquid crystals from europium nitrate and P123 with enhanced luminescence efficiency.

Fabrication of lyotropic aggregates containing the lanthanide ions is becoming a preferable way to prepare novel functional materials. Here, the lyotropic liquid crystals (LLCs) of reverse hexagonal, reverse bicontinuous cubic, and lamellar phases have been constructed in sequence directly from the mixtures of Eu(NO3)3·6H2O and Pluronic P123 amphiphilc block copolymer with increasing the salt proportion. Their phase types and structural characteristics were analyzed using polarized optical microscopy (POM) and small-angle X-ray scattering (SAXS) measurements. The driving forces of reverse LLC phase formation were investigated using Fourier-transformed infrared spectroscopy (FTIR) and rheological measurements. The hydrated europium salt was found to act not only as a solvent here, but also as the bridge to form hydrogen bonding between coordinated water molecules and PEO blocks, which played a key role in the reverse LLCs formation. Compared to those in aqueous solutions and solid state, the enhanced luminescence quantum yields and prolonged excited state lifetimes were observed in two europium containing reverse mesophases. The luminescence quenching effect of lanthanide ions was efficiently suppressed, probably due to the substitution of coordinated water molecules by oxyethyl groups of P123 and ordered phase structures of LLCs, where the coordinated europium ions were confined and isolated by PEO blocks. The optimum luminescence performance was then found to exist in the reverse hexagonal phase. The obtained results on such lanthanide-induced reverse LLCs should be referable for designing new luminescent soft materials construction to expand their application fields.

Phase transition of a quaternary ammonium Gemini surfactant induced by minor structural changes of protic ionic liquids.

The aggregation behaviors of a Gemini surfactant [C12H25(CH3)2N(+)(CH2)2N(+)(CH3)2C12H25]Br2(-) (12-2-12) in two protic ionic liquids (PILs), propylammonium nitrate (PAN) and butylammonium nitrate (BAN), were investigated by means of several experimental techniques including small and wide-angle X-ray scattering, the polarized optical microscopy and the rheological measurement. Compared to those in ethylammonium nitrate (EAN), the minor structural changes with only one or two methylene units (-CH2-) increase in cationic chain length of PIL, result in a dramatic phase transition of formed aggregates. The critical micellization concentration was increased in PAN, while no micelle formation was detected in BAN. A normal hexagonal phase was observed in the 12-2-12/PAN system, while the normal hexagonal, bicontinuous cubic, and lamellar phases were mapped in the 12-2-12/BAN system. Such aggregation behavior changes can be ascribed to the weaker solvophobic interactions of 12-2-12 in PAN and BAN. The unique molecular structure of 12-2-12 is also an important factor to highlight such a dramatic phase transition due to the PIL structure change.

Lyotropic liquid crystalline phases of a phytosterol ethoxylate in amide solvents.

Materials exhibiting unique aggregation behavior in nonaqueous solvents have attracted attention due to their wide applications. Motivated by this recent interest, the aggregation properties of a phytosterol ethoxylate surfactant, BPS-10, in three organic amide compounds, formamide (FA), N-methylformamide (NMF), and N,N-dimethyl- formamide (DMF), have been studied. Polarized optical microscopy and small-angle X-ray scattering techniques were used to investigate the lyotropic liquid crystalline (LLC) phases formed in these binary systems. Herein, we discuss the relationship between subtle intermolecular interactions and the aggregation behavior of BPS-10. As good proton donors or acceptors to form hydrogen bonding, FA molecules allow BPS-10 to show a richer phase behavior. Compared with the systems formed in water and ionic liquids, the LLCs constructed in FA have higher thermal stability. In addition, two kinds of lamellar phases could coexist in a narrow region. With the methyl replacement in formamide, however, the ability to form hydrogen bonds is reduced and the solvent bulk phase structure becomes less ordered from FA to DMF. Consequently, the solvophobic interaction of BPS-10 becomes weaker, and the LLCs are more difficult to form. In addition, the extra strong interactions between the steroid rings of BPS-10 may provide enough driving force to produce the hexagonal phase (H1) directly in NMF and DMF without micelle formation, thereby creating a novel sequence (isotropic → H1 → Lα) of ordered phases with increasing surfactant concentration. The results discussed herein should prove to be a useful complement to the growing body of literature regarding steroid surfactant aggregation in polar organic solvents.

Wormlike micelles formed using Gemini surfactants with quaternary hydroxyethyl methylammonium headgroups.

The aggregation behavior of Gemini surfactants with hydroxyl groups in their headgroups, butane-1,4-bis(hydroxyethyl methylalkylammonium) bromides hereafter abbreviated as m-4-m MEA (m = 12, 14, 16), has been investigated in aqueous solution. Each formed a viscous fluid in water at low concentration in the absence of a salt. In solutions of 14-4-14 MEA, the formation of highly viscoelastic wormlike micelles could be detected using steady and dynamic rheological measurements. The existence of these long column micelles has also been confirmed using cryo-transmission electron microscopy (cryo-TEM) and small angle X-ray scattering (SAXS). Compared with conventional bis(dimethylalkylammonium) bromide Gemini molecules with the same spacer (14-4-14), 14-4-14 MEA demonstrated a better ability to fabricate wormlike micelles because of the change in the headgroup structure. As for 16-4-16 MEA, which has longer alkyl chains, its aqueous solutions behave more like elastic gels at a concentration of 80 mmol L(−1). The unique viscoelastic behavior of m-4-m MEA in water can be attributed to the synergistic interactions of hydrophobic attraction and hydrogen bonding. The obtained results are believed to be an important addition to the effect that the headgroups of Gemini surfactants have on their aggregation behavior in dilute solutions.