Hexagonal Lyotropic Liquid Crystal Research Articles

An insight into physicochemical properties of hexagonal lyotropic liquid crystal templates from amphiphiles for mesoporous structural administration

Hexagonal lyotropic liquid crystals (HLLC) provide an ideal template for the fabrication of nanofiltration membranes without the flux-selectivity trade-off problem. Amphiphiles, the core components of the columnar micelles in the HLLC system, play a key role in regulating the nanostructure, their effects on dimensional stability and physicochemical properties of the system however have not been explored well. In this research, we compared the dimensional stability and physicochemical properties of HLLC templates prepared from amphiphiles with various head groups and tail lengths. The amphiphiles with charged head groups (dodecyl trimethylammonium bromide, DTAB, and hexadecyl trimethylammonium bromide, CTAB) enable more monomers to be introduced and a much smaller (∼ 1/2) pore size than that with uncharged ones (polyethylene glycol hexadecyl ether, Brij56). The tail length however mainly regulates the width of water channels with CTAB being 23.27 Å and DTAB about 17.06 Å when the head groups are identical. Although the HLLC systems with CTAB and DTAB present a little bit higher phase transition temperature, the dynamic mechanical stability is much better than that with Brij56 at room temperature, facilitating the reorientation process under an electric force with the order parameter reaching to about 0.9 and the retention of the aligned nanostructure with the absence of the force at room temperature. The study enables a better understanding of the effects of amphiphiles on HLLC templates and their tunability for advanced nanofiltration membranes.

Interfacial design of support substrate for a continuous mesophase-templated active layer with adjustable pore size

Nano-porous active layers templated by hexagonal lyotropic liquid crystal (HLLC) offer a continuous water pathway, rendering them promising for membrane separation applications of high performance. The surface properties, such as surface roughness, hydrophilicity and pore size, of commercially available ultrafiltration membranes usually need to be optimized to better support the active layer. Here, we apply a facile yet potent thermal treatment process to a polyacrylonitrile ultrafiltration (UPAN) substrate and form a continuous HLLC separation layer. The enhancement in water filtration performance is largely influenced by the surface roughness of the substrates. As the temperature increases, the UPAN substrates become rougher due to approaching the glass transition temperature of polyacrylonitrile. This leads to a denser HLLC active layer with smaller pores. For the membranes treated at a temperature of 100 °C, their water flux reaches 17 L/m2h, which is 10 times higher than that of the membranes treated at 85 °C, and the PEG4000 rejection increases by almost 50 % from 42 % to 59 %. This heat treatment process offers a novel approach to fabricate mesophase-templated active layers with adjustable pore sizes, thus advancing membrane separation techniques.

Aggregation behaviours of sulfobetaine zwitterionic surfactants in EAN

Ionic liquids have become one kind of the most promising solvents for self-assembly. The aggregation behaviours of various surfactants have been studied in numerous ionic liquids, especially the cationic and nonionic surfactants. In this work, we would explore the aggregation behaviours of sulfobetaine zwitterionic surfactants (SB3-n, n = 12, 14, 16) in the protic ionic liquid ethylammonium nitrate (EAN). The micellization behaviour was studied by surface tension measurement and the critical micellization concentrations are much larger than those in water. The micellar phase and hexagonal lyotropic liquid crystal phase are formed by SB3-12 and SB3-14 in EAN while an additional micellar cubic lyotropic liquid crystal phase is formed in the SB3-16/EAN system. The structure of aggregates was characterized by the small angle X-ray scattering while optical and viscoelastic properties by polarized optical microscopy and rheology. The alkyl chain length effect of SB3-n on aggregation behaviours was discussed and compared with those in the other surfactant/EAN systems. Our results would provide the thorough understanding on aggregation behaviours of sulfobetaine zwitterionic surfactants in EAN.

The characterization of hexagonal lyotropic liquid crystal nanostructure: effects of polymer tail length

The characterization of hexagonal lyotropic liquid crystal nanostructure: effects of polymer tail length

The effect of alkyl chain length of the imidazole ionic liquid surfactants on the improving lubricating properties of the hexagonal lyotropic liquid crystal composed of the [C16imCn]Br/hydrotalcite/H2O

The hydrotalcites were dispersed in the hexagonal lyotropic liquid crystals (LLCs) composed of 1-hexadecyl-3-alkyl imidazolium bromide ([C16imCn]Br, n = 1, 2 and 3) and H2O. The effects of the hydrotalcite concentration and the alkyl chain length of the [C16imCn]Br on the properties and the lubricant performance of the [C16imCn]Br/hydrotalcite hexagonal LLCs were studied by small angle X-ray diffraction measurements, rheology and tribology. Compared with the pure hexagonal LLCs, the incorporation of hydrotalcite into the [C16imCn]Br hexagonal LLCs can increase the interlayer distances and the viscoelasticity of the hybrid hexagonal LLCs gradually. However, the friction coefficient and wear volume decrease firstly and then increase with the increasing of hydrotalcite content. With the increase of the alkyl chain length of the [C16imCn]Br, the viscoelasticity, the interlayer distance and the water permeability of the mixed LLCs gradually increase which decreases the friction coefficient and wear volume at the moderate hydrotalcite content. The mechanism of the effective improvement of lubrication performance of the hybrid hexagonal LLCs is the tribofilm formed by the physical adsorption and tribochemical reaction of [C16imCn]Br/hydrotalcite LLCs on the steel surface.

Towards a High-Flux Separation Layer from Hexagonal Lyotropic Liquid Crystals for Thin-Film Composite Membranes.

Hexagonal lyotropic liquid crystals (HLLC) with uniform pore size in the range of 1~5 nm are highly sought after as promising active separation layers of thin-film composite (TFC) membranes, which have been confirmed to be efficient for water purification. The potential interaction between an amphiphile-based HLLC layer and the substrate surface, however, has not been fully explored. In this research, hydrophilic and hydrophobic microporous polyvinylidene fluoride (PVDF) substrates were chosen, respectively, to prepare TFC membranes with the active layers templated from HLLC, consisting of dodecyl trimethylammonium bromide, water, and a mixture of poly (ethylene glycol) diacrylate and 2-hydroxyethyl methacrylate. The pore size of the active layer was found to decrease by about 1.6 Å compared to that of the free-standing HLLC after polymerization, but no significant difference was observable by using either hydrophilic or hydrophobic substrates (26.9 Å vs. 27.1 Å). The water flux of the TFC membrane with the hydrophobic substrate, however, was higher than that with the hydrophilic one. A further investigation confirmed that the increase in water flux originated from a much higher porosity was due to the synergistic effect of the hydrophilic HLLC nanoporous material and the hydrophobic substrate.

Characterization of hexagonal lyotropic liquid crystal microstructure: Effects of vitamin E molecules

The effects of vitamin E (VE) on the liquid crystal behavior and structure of a lyotropic liquid crystal (LLC) system based on nonionic surfactant C12EO10/H2O are reported. Polarized optical microscopy, X-ray diffraction and FTIR combined with fluorescent analysis were utilized to study structural properties and the interactions between the vitamin E and hexagonal mesophase. It was revealed that up to 20 wt% VE is solubilized within the direct hexagonal mesophase. As a result, the lattice parameter and the melting point increased as compared with binary LLC C12EO10/H2O. The presence in the system C12EO10/H2O of VE in the amount above 30% (up to 60 wt%) leads to a structural transformation of the mesophase from the direct to reverse hexagonal mesophase. The structural changes of hydrophilic and hydrophobic domains in the presence of VE in LLC were characterized.

Temperature-sensitive lyotropic liquid crystals as systems for transdermal drug delivery

The purpose of this study was to develop temperature-sensitive lyotropic liquid crystals (LLC) for transdermal drug delivery systems. The hexagonal and cubic LLC samples were constructed in the polyoxyethylene (20) sorbitan monooleate (Tween 80)/PEG-60 hydrogenated castor oil (RH 60)/Ethyl oleate (EtOL)/water (H2O) system and characterized by Small Angle X-ray Scattering (SAXS), low field nuclear magnetic resonance (LF-NMR) and rheology. Additionally, its skin permeation behavior in vitro and cell-stimulating studies were investigated as well. The LLC system exhibited temperature sensitivity. Under the influence of temperature, the structure of LLC collapsed and was transformed into micellar solution. While, sample S3 (water content was 35 wt%.) was transformed from cubic LLC to hexagonal LLC then to micellar solution as temperature increased. The compositions and the introduction of paeonol both can influence the structure of LLC, and were used to adjust the phase transition temperature to close to the human body temperature. In vitro transdermal experiments showed that the release behavior of paeonol-loaded LLC was obviously temperature-sensitive and controlled by concentration diffusion. In vitro cell-stimulating studies displayed that LLC samples exhibited no obvious toxicity. The above results indicated that the temperature-sensitive LLC had potential to be applied as a transdermal drug delivery system.

Spacer length effect on the aggregation behaviours of gemini surfactants in EAN

As the symbol of gemini surfactants, the spacer group connects two surfactant monomers and plays an important role in the self-assembling of gemini surfactants. Recent attention has been paid to the effects of spacer nature and length in aqueous systems. In this study, the aggregation behaviours of quaternary ammonium gemini surfactants 12-s-12 with different spacer length (s = 2, 3, 4, 5, 6, 8, 10, 12) have been investigated in the protic ionic liquid EAN. The micellization behaviour was characterized by surface tension measurement. With the help of small-angle X-ray scattering (SAXS), the size and shape of aggregates were verified. The spacer length effect could be reflected by the changes in the micellization and phase behaviours of 12-s-12/EAN systems. The critical packing parameter of gemini molecules would decrease monotonically with the spacer length, which is supported by SAXS results. Due to the charge screening effect of EAN, the aggregation behaviours of 12-s-12 would be mainly influenced by spacer length. Our results would be the important supplement to the spacer length effect of gemini surfactants in the nonaqueous systems. With the increase of spacer chain length, the reverse hexagonal lyotropic liquid crystal phase would transform into the micellar phase.

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.

Evolution of structural dimensions in mesoporous template precursor from hexagonal lyotropic liquid crystals

Producing nanopores from hexagonal lyotropic liquid crystals (LLCs) templates requires not only retaining phase morphology of the templates but also precisely controlling structural dimensions of unit cells. In this study, SAXS and 2H NMR are used to investigate dimensional evolutions of ternary systems consisting of polymerizable species, (ethylene glycol) diacrylate (PEGDA) and/or 2-hydroxyethyl methacrylate (HEMA), in a LLCs template of hexagonally packed cylinders formed from dodecyl trimethylammonium bromide (DTAB) and water. With the addition of those polymerizable species, the system rearranges into a new hexagonal system with a smaller aggregation number, smaller pores and a thicker pore wall thickness. The hexagonal system will coexist with an aqueous-rich phase containing isotropically distributed DTAB if sufficient PEGDA is applied but the single hexagonal system could be restored by partially replacing the PEGDA with HEMA. The mobility of DTAB molecules within the aggregates varies depending on monomer compositions. The changes in structural dimensions of the unit cells and phase behaviors after adding polymerizable monomers allow dimensional control of mesochannels and potentially enable the control of selectivity and robustness of polymerized nanomaterials via molecular design.

Luminescent Vesicles and Lyotropic Liquid Crystals in Ethylammonium Nitrate from a Partially Amphiphilic Eu Complex.

Soft luminescent materials have attracted much attention because of their self-assembled and controllable properties. To explore their facile and effective fabrication ways, we report here the self-assembling of luminescent vesicles and lyotropic liquid crystals (LLCs) in a protic ionic liquid, ethylammonium nitrate, by a partially amphiphilic europium β-diketonate complex (Eu(III)) with a 1-dodecyl-3-methylimidazolium cation as the counter ion. An interesting result came from the complex-induced vesicle formation of corresponding amphiphile, 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br), which has been rarely reported in the past. It was the interaction between the Eu(III) and imidazolium group that changed the critical packing parameter of [C12mim]Br, which finally resulted in the occurrence of vesicles. The obtained vesicle aggregates exhibited enhanced fluorescence intensity and lifetime compared to those of Eu(III) solution. Meanwhile, a hexagonal LLC phase with better fluorescence properties was found at higher [C12mim]Br concentration. The obtained photophysical data confirmed that the order degree of Eu(III)-containing aggregates could effectively increase the energy transition efficiency of ligands. The better luminescent properties of LLC resulted from the stronger stabilizing and binding effects on Eu(III) in LLC than that in vesicles, which might be caused by closer molecular packing in LLC. The results presented here will not only expand the strategy of constructing lanthanide-containing luminescent soft materials in ionic liquids but also provide reference to better understand the effect of organized aggregates on luminescence properties.

In Situ SAXS Measurement and Molecular Dynamics Simulation of Magnetic Alignment of Hexagonal LLC Nanostructures.

The alignment of nanostructures in materials such as lyotropic liquid crystal (LLC) templated materials has the potential to significantly improve their performances. However, accurately characterising and quantifying the alignment of such fine structures remains very challenging. In situ small angle X-ray scattering (SAXS) and molecular dynamics were employed for the first time to understand the hexagonal LLC alignment process with magnetic nanoparticles under a magnetic field. The enhanced alignment has been illustrated from the distribution of azimuthal intensity in the samples exposed to magnetic field. Molecular dynamics simulations reveal the relationship between the imposed force of the magnetic nanoparticles under magnetic field and the force transferred to the LLC cylinders which leads to the LLC alignment. The combinational study with experimental measurement and computational simulation will enable the development and control of nanostructures in novel materials for various applications.

Synthesis and Characterization of Zirconia Nanoparticles by Combining Sulfated Hydroxy Zirconyl and Nitrated Hydroxy Zirconyl in Hexagonal Phase Lyotropic Liquid Crystal

Synthesis and Characterization of Zirconia Nanoparticles by Combining Sulfated Hydroxy Zirconyl and Nitrated Hydroxy Zirconyl in Hexagonal Phase Lyotropic Liquid Crystal

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

HypothesisThe 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. ExperimentsHere, 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. FindingsThe 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.

Ultrathin Uniform Platinum Nanowires via a Facile Route Using an Inverse Hexagonal Surfactant Phase Template.

We present an attractive method for the fabrication of long, straight, highly crystalline, ultrathin platinum nanowires. The fabrication is simply achieved using an inverse hexagonal (HII) lyotropic liquid crystal phase of the commercial surfactant phytantriol as a template. A platinum precursor dissolved within the cylindrical aqueous channels of the liquid crystal phase is chemically reduced by galvanic displacement using stainless steel. We demonstrate the production of nanowires using the HII phase in the phytantriol/water system which we obtain either by heating to 55 °C or at room temperature by the addition of a hydrophobic liquid, 9- cis-tricosene, to relieve packing frustration. The two sets of conditions produced high aspect nanowires with diameters of 2.5 and 1.7 nm, respectively, at least hundreds of nanometers in length, matching the size of the aqueous channels in which they grow. This versatile approach can be extended to produce highly uniform nanowires from a range of metals.

Toward the Fabrication of Advanced Nanofiltration Membranes by Controlling Morphologies and Mesochannel Orientations of Hexagonal Lyotropic Liquid Crystals.

Water scarcity has been recognized as one of the major threats to human activity, and, therefore, water purification technologies are increasingly drawing attention worldwide. Nanofiltration (NF) membrane technology has been proven to be an efficient and cost-effective way in terms of the size and continuity of the nanostructure. Using a template based on hexagonal lyotropic liquid crystals (LLCs) and partitioning monomer units within this structure for subsequent photo-polymerisation presents a unique path for the fabrication of NF membranes, potentially producing pores of uniform size, ranging from 1 to 5 nm, and large surface areas. The subsequent orientation of this pore network in a direction normal to a flat polymer film that provides ideal transport properties associated with continuous pores running through the membrane has been achieved by the orientation of hexagonal LLCs through various strategies. This review presents the current progresses on the strategies for structure retention from a hexagonal LLCs template and the up-to-date techniques used for the reorientation of mesochanels for continuity through the whole membrane.

Lyotropic liquid crystal-assisted synthesis of micro- and nanoparticles of silver

ABSTRACTA simple, one-step approach for the synthesis of micro- and nanoparticles of silver by employing a lyotropic liquid crystal (LLC) template is described. Anisotropic silver particles are synthesised by reducing an appropriate amount of precursor silver nitrate using a mild reducing agent ascorbic acid in presence of a hexagonal LLC medium, without the aid of any external stabilising agents. In this synthesis, precursor concentration, type of the reducing agent and LLC phase are found to significantly influence the particle size and morphology. Either a decrease in the concentration of silver nitrate or a change in the reducing agent, from ascorbic acid to sodium borohydride in the same reaction medium, yielded quasi-spherical nanoparticles. Besides, replacing the hexagonal LLC medium with a lamellar phase during the synthesis using ascorbic acid also resulted in the formation of spherical particles in nanometre scale. As a comparison, gold nanoparticle synthesis is carried out in hexagonal and lamellar LLC phases. Similar to the observations made in the silver particle synthesis, branched anisotropic particles are formed in the hexagonal phase and quasi-spherical particles are produced in the lamellar phase. A possible growth mechanism for the formation of these particles based on the phase structure of the LLC medium is discussed.

Radiolytic syntheses of hollow UO2 nanospheres in Triton X-100-based lyotropic liquid crystals

Abstract Hollow nanospheres (ϕ: 60–80 nm, wall thickness: 10–20 nm), consisted of UO2 nanoparticles (ϕ: 3–5 nm), were successfully prepared in a Triton X-100-water (50:50, w/w) hexagonal lyotropic liquid crystal (LLC) by γ-irradiation, where water soluble ammonium uranyl tricarbonate was added as precursor. The product was stable at least up to 300°C. Furthermore, whether the nanospheres were hollow or not, and the wall thickness of the hollow nanospheres could be easily controlled via adjusting dose rate. While in the Triton X-100 based micellar systems, only solid nanospheres were obtained. At last, a possible combination mechanism containing adsorption, aggregation and fracturing processes was proposed.

Lyotropic liquid crystals fabricated in ionic liquids

The lyotropic liquid crystals (LLCs) are one important kind of aggregates formed by surfactants in solvent media and have wide applications in nanomaterial systhesis, chemical reaction environment, drug delivery, lubricating material, oil recovery and so on. Meanwhile, the ionic liquids (ILs) have currently widely used as novel nonaqueous media in the areas of organic synthesis and catalysis, biochemical engineering, materials science, electrochemistry, carbohydrate chemistry, and separation techniques for their unique characteristics of low melting temperature, negligible vapor pressure, wide electrochemical window, nonflammability, good catalytic properties, high thermal stability, and ionic conductivity. For these reasons, more and more attention has been paid to ILs as the self-assembly media. Among them, the LLCs formed by surfactants in ILs have received increasingly studies. Exploration on the LLC behaviors of surfactants in ILs may provide not only a better understanding of intermolecular actions in self-assembly, but also certain new properties to LLCs, like better thermostability compared to those constructed in aqueous media. For these reasons, this account here reviews the LLC phase behaviors in ILs of various surfactants, including quarternary ammonium cationic surfactant, alkyl polyoxyethylene nonionic surfactant and Pluronic block copolymer. For the cationic surfactants, several single chain molecules like the hexadecyltrimethylammonium bromide, 1-hexadecyl-3-methylimidazolium chloride, and N-hexadecyl-N-methylpyrrolidinium bromide, their phase behaviors in various ILs were summaried. Various LLC phases including the normal hexagonal, lamellar, and reverse bicontinuous cubic LLC phases could be detected in ethylammonium nitrate (EAN). The hexagonal LLC phase with better thermostability was formed in EAN compared to that in water. For the molecule with two alkyl chains on one head, the dimethyldidodecylammonium bromide, the sponge and lamellar phases were observed in EAN and the sponge phase could be extended to larger region than that in aqueous system. Unlike the single chain surfactants, the reverse hexagonal phases were observed in the quarternary ammonium Gemini surfactants/EAN systems, which were not observed in corresponding water media. With increasing the chain length of one or two ethylene groups in cation of EAN, that is, from EAN to PAN or BAN, the normal LLC phases were formed back. As for the polyoxyethylene nonionic surfactants (C n E m ) in EAN, their phase behaviors were similar to those in water. Due to the weaker solvophobic interactions in EAN than in water, the longer alkyl chains were necessary for the formation of LLC. While in aprotic ILs, no LLC phase was observed. However, for the phytosterol ethoxylate surfactants (BPS-n), the LLC phases were observed both in EAN and also in aprotic ILs like [Bmim]BF4 and [Bmim]BF6. Similar aggregation behaviors were also observed for Pluronic block copolymer in EAN and [Bmim]BF4. The difference in phase behaviors of these surfactants in various ILs was analyzed by Gordon parameter, which was a measure of the cohesive energy density of the solvent. Generally speaking, ILs with higher Gordon parameters are correspondent to greater LLC diversity and better thermostability. The protic ionic liquids, which are capable of accepting protons and form hydrogen bonding network, would have a stronger ability of supporting surfactant self-assembly than the aprotic ionic liquids. This is the reason why richer phases are usually formed in EAN than in [Bmim]BF4 and [Bmim]BF6. Based on the review, the perspective for future research in this area has been also provided, such as synthesis of novel kinds of ILs and surfactants and investigation on new self-assembly systems.