Lyotropic Liquid Crystal Phases Research Articles

ChemInform Abstract: Silica-Based, Cubic Mesostructures: Synthesis, Characterization, and Relevance for Catalysis

We review the formation mechanism, synthetic history and catalytic applications of the cubic phases of mesoporous silica. MCM-48 and SBA-1, analogous to surfactant lyotropic liquid crystal phases, possess a three-dimensional pore array, a 15–30 A pore aperture and a narrow pore size distribution. Evidence for intermediate range order within the silicate walls based on PAS-FTIR spectra will be discussed. Isomorphic heteroatom substitution of aluminum and a number of transition metals has been achieved by both hydrothermal and post-synthetic methods in order to modify the surface activity of these materials. Modified materials containing fully oxidized, early transition metals were found to be catalytically active for photocatalytic reduction of CO2 with water as well as peroxidative oxidation and halogenation of large organic substrates.

Single-Walled Carbon Nanotube/Lyotropic Liquid Crystal Hybrid Materials Fabricated by a Phase Separation Method in the Presence of Polyelectrolyte

We present a detailed study on the incorporation of single-walled carbon nanotubes (SWNTs) into lyotropic liquid crystals (LLC) by phase separation in the presence of polyelectrolytes. Two cases were studied in this work: (i) incorporation of SWNTs into the LLC phase formed by an anionic surfactant sodium dodecyl sulfate (SDS) in the presence of an anionic polyelectrolyte poly(sodium styrenesulfonate) (PSS); (ii) incorporation of SWNTs into the LLC phase formed by a cationic surfactant cetyltrimethylammonium bromide (CTAB) in the presence of a cationic polyelectrolyte poly(diallydimethylammonium chloride) (PDADMAC). The SWNTs/LLC composites were characterized by polarized optical microscopy (POM) observations and small-angle X-ray scattering (SAXS) measurements. In both systems, the surfactant phase was condensed into a hexagonal lattice by the polyelectrolyte within the investigated concentration range. Several factors that can influence the property of SWNTs/LLC composite were examined, including concentration of surfactants and polyelectrolytes and temperature. Aggregated SWNTs were not observed, indicating that SWNTs were well dispersed in the LLC phases. SAXS measurements showed the lattice parameter of the host LLC phase changed upon varying the mixing ratio of polyelectrolyte to ionic surfactant. The SWNTs/LLC hybrids showed considerable stability against temperature rise in both systems, and desorption of surfactant from SWNTs was not observed at higher temperature.

Color Tunable Novel Amphotropic Liquid Crystalline Acrylate End-capped with a Cholesteryl Group

Abstract We report a novel, monomeric, lyotropic, cholesteric liquid crystal revealing selective reflection in the visible light region and having photochromic properties in the lyotropic liquid crystal phase. Monomer (+)-cholesteryl (6-acryloyloxyhexyloxy)-4-cinnamate was synthesized. Liquid crystal phases of M1 were identified using polarized optical microscopic and X-ray diffraction methods. Reflection light spectra were analyzed using an optical fiber system.

Synthesis of gold nanogears, nanobelts and nanoplates in hexagonal phase of lyotropic liquid crystal

Single crystalline planner gold nanostructures, including nanogears, nanobelts and nanoplates, are synthesised in hexagonal lyotropic liquid crystals made of P123/HAuCl4 aqueous solution. The effects of reaction temperature as well as capping agent on the growth of nanoproducts are studied in detail. When cetyltrimethyl ammonium bromide is used as the capping agent, gold nanobelts appear in the products at 45°C, while gold nanogears can be obtained with a large scale at room temperature when poly(N-vinyl-2-pyrrolidone) is the capping agent. Results show that temperature is an important factor that may influence the growth of gold nanoproducts through changing the lyotropic liquid crystal structure and the adsorption process of capping agent on nanocrystal surfaces. The growth mechanism of nanostructures is further certified by the products from the microwave assistant method.

High Pressure Static and Time-Resolved X-Ray Studies of Inverse Phases in Cholesterol / Lipid Mixtures

Non-bilayer phases are thought to be of considerable biological relevance. Whenever there is a topological change in the membrane, corresponding to events such as membrane fusion, non-bilayer structures are assumed to be adopted locally. Several complex three-dimensional lyotropic liquid crystal phases are already known, such as the bicontinuous cubic phases, but for many years only a single example was found - a cubic phase of spacegroup Fd3m - of a structure based upon a complex close packing of inverse micelles. We have recently reported the discovery (1) of a novel lyotropic liquid crystal phase, of spacegroup, P63/mmc, whose structure is based upon a hexagonal close packing of identical quasi-spherical inverse micelles.Although a plethora of equilibrium phase diagrams have been published, there is a scarcity of knowledge regarding the kinetics and mechanisms of lyotropic phase transitions. If we are to further our knowledge of events such as membrane fusion then a comprehensive understanding of the processes governing phase transitions, the type of intermediates formed and the mechanism by which a transition occurs are vital.A superb technique for monitoring and initiating the structural evolution of such systems, in the millisecond regime, is time resolved X-ray diffraction, using pressure as the trigger mechanism. We have employed this technique to investigate lamellar - non-lamellar (P63/mmc phase) transition kinetics in cholesterol/ phospholipid/ diacylglycerol model membrane systems. Equilibrium pressure - temperature composition diagrams have been constructed, allowing us to choose appropriate pressure-jump parameters (temperature, initial and final pressures) for the kinetic studies.(1) G. C. Shearman, A. I. I. Tyler, N. J. Brooks, R. H. Templer, O. Ces, R. V. Law, J. M. Seddon, J. Am. Chem. Soc.131, 1678 (2009)

Self-assembly of an amyloid peptide fragment–PEG conjugate: lyotropic phase formation and influence of PEG crystallization

The self-assembly of polymer–peptide conjugates containing a modified amyloid peptide sequence is studied. Lyotropic liquid crystal phases are observed in water, and PEG crystallization is probed.

Polymerization Kinetics and Nanostructure Evolution of Reactive Lyotropic Liquid Crystals with Different Reactive Group Position

The synthesis of polymers with inherent nanostructure has recently received much attention because of the wide range of potential application in which these materials could be used. To understand the factors that affect the nanoscopic order preservation upon polymerization, this work examines the influence of reactive group position in polymerizable surfactants that form reactive lyotropic liquid crystals (LLCs) on polymerization kinetics and order before and after polymerization. Less ordered LLC phases are formed with reactive surfactants bearing reactive groups in the nonpolar tail compared to reactive surfactants with reactive groups near the polar head. The polymerization kinetics are influenced by both the LLC order and the position of the reactive group. Higher polymerization rates are observed for reactive surfactants with the reactive group near the polar head with increasing surfactant concentration and LLC order. On the other hand, lower polymerization rates are observed for the reactive surfactant with the reactive group in the aliphatic tail at higher surfactant concentrations and LLC order. This behavior is mainly due to segregation of the reactive groups in different regions of the LLC phases as indicated by an apparent increase in both the propagation and termination kinetic constants. When using initiators that induce higher polymerization rates, greater LLC order preservation is observed after polymerization. Also, by using higher light intensities, the resulting polymer exhibits higher degrees of LLC order retention than that observed when polymerization is initiated with lower light intensities and corresponding lower polymerization rate.

Predictive synthesis of ordered mesoporous silica with maltoside and cationic surfactants based on aqueous lyotropic phase behavior

Self-assembled nonionic alkyl glycoside surfactants are of interest for creating functional adsorption and catalytic sites at the surface of mesoporous sol-gel-derived materials, but they typically impart poor long-range order when they are used as pore templates. Improved order and control over the functional site density can be achieved by mixing the alkyl polyglycoside surfactant with a cationic surfactant. Here, we investigate the rarely reported lyotropic liquid crystalline (LLC) phase behavior of aqueous solutions of a nonionic disaccharide surfactant, n-dodecyl-beta-d-maltoside (C(12)G(2)/DM), and cetyltrimethylammonium bromide (C(16)TAB) by low-angle powder X-ray diffraction (XRD) and polarized optical microscopy (POM). An approximate ternary phase diagram of the C(16)TAB-C(12)G(2)-water system is developed at 50 degrees C, which includes 2-D hexagonal (P6mm symmetry), bicontinuous cubic (Ia3 d symmetry), lamellar, and rectangular (cmm symmetry) LLC phases. By replacing the volume of water in the phase diagram with an equivalent volume of silica, ordered mesoporous materials are prepared by a nanocasting technique with variable C(12)G(2)/C(16)TAB ratios. For large regions of the phase diagram, this approach is predictive. However, silica materials synthesized with comparatively high C(12)G(2)/C(16)TAB ratios are only poorly ordered in a way that does not correspond to their lyotropic liquid crystalline phase behavior. Also, in contrast with our previous study of mixed C(16)TAB/n-octyl-b-d-glucopyranoside templating [37] the boundary between hexagonal and bicontinuous cubic materials is shifted towards higher surfactant content than in the aqueous LLC system.

Spontaneous self-assembly of nucleic acids: liquid crystal condensation of complementary sequences in mixtures of DNA and RNA oligomers

“Le cose tutte quante hanno ordine tra loro, e questo e’ forma che l’universo a Dio fa simigliante.” (Dante Alighieri, Divina Commedia, Paradiso, I, 103) [All things whate’er they be Have order among themselves, and this is form, That makes the universe resemble God] A remarkable example of spontaneous self-assembly of biomolecules, driven purely by physical interactions, is reported. Short, complementary DNA and RNA oligomers, down to six bases in length, exhibit lyotropic liquid crystal phases, chiral nematic and columnar, although these duplexes lack the shape anisotropy required for liquid crystal ordering. Such phases are produced by the end-to-end stacking of the duplex oligomers into polydisperse, anisotropic, rod-shaped aggregates, which can order into liquid crystals. Furthermore, when only a fraction of the sample is composed of complementary sequences, and hence the solution is effectively a mixture of single strands and double-stranded helices, the system is found to phase separate with duplex-rich liquid crystalline domains emerging from an isotropic background rich in single strands. This spontaneous partitioning, resulting from a combination of entropic and enthalpic factors, is sensitive to the degree of complementarity of the sequences and can be tuned with temperature. We suggest that in a chemical environment where oligomer ligation is possible, such ordering and condensation could provide a plausible route for the selective synthesis of extended complementary oligomers, a mechanism of possible relevance in prebiotic scenarios.

Oriented and low‐density tin dioxide film by sol–gel mineralizing tin‐contained hydroxypropyl cellulose lyotropic liquid crystal for laser‐induced extreme ultraviolet emission

AbstractA series of tin‐doped hydroxypropyl cellulose (HPC) lyotropic liquid crystal (LC) was synthesized using a simple process and their properties were characterized using selective reflection, wide‐angle X‐ray diffraction (WAXD), and the band texture observed under polarized optical microscope. The present preparation is applicable for mass production using large substrate with low cost HPC. A cholesteric lyotropic LC phase was observed for the hybrid solution with higher than 40 wt % HPC. After sol–gel condensation, the HPC‐Sn hybrid LC films were calcined at 400 °C and the as‐prepared product was determined to obtain tin dioxide (SnO2) which was characterized using WAXD. The iridescent color and ∼2 nm structure seen after the condensation disappeared in the as‐prepared SnO2. Scanning electronic microscope images of the SnO2 showed that the HPC content in the HPC‐Sn hybrid played an important role in controlling the SnO2 morphology. A spectrum of relatively monochromatic extreme ultraviolet (13.5 nm) emission was measured in the as‐prepared SnO2 in comparison with bulk tin and inverse opal SnO2. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4566–4576, 2009

Electrolyte Effects on the Stability of Nematic and Lamellar Lyotropic Liquid Crystal Phases: Colligative and Ion-Specific Aspects

We investigated the electrolyte effects on the stability of nematic and lamellar lyotropic liquid crystalline (LLC) phases formed by the simple anionic surfactant cesium pentadecafluorooctanoate (CsPFO) in water. To the lyotropic guest phase, at the constant CsPFO-mass fraction of 0.55, the series of electrolytes LiCl, NaCl, KCl, CsCl, CsI, and Cs(2)SO(4), respectively, was added at concentrations ranging from 0.5 to 2.5 mol %. With increasing electrolyte concentration two substantially different effects were observed. At low concentrations all added electrolytes caused an increase of the thermal stability of the LLC phases, favoring the lamellar phase over the nematic phase. This behavior is, at least qualitatively, understood within the packing parameter model. The extent of the stabilization clearly depends on the chemical nature of the added cation. For a given cation, however, the effect is colligative, i.e., independent of the chemical nature of the added anion. At higher salt concentrations a salting-out-like phase separation was induced. This effect is clearly ion-specific as the salting-out concentration varied for each cation following the order of the Hofmeister series for cations.

Aging and yielding in a sheared AOT/iso-octane/water lyotropic lamellar phase

We define a creep-flow-based measurement procedure to allow reliable and reproducible results on aging and yielding materials to be obtained. Investigation of the effects of different parameter such as the pre-shear time, the recovery time and the applied stress magnitude on the viscoelastic properties of a lyotropic liquid crystal phase is reported. Cryo-TEM observations indicate the formation of multiconnected bilayers at rest. Shearing the investigated material shows a propensity to acquire all the macroscopic properties of "soft jammed systems". These properties are then interpreted in terms of shear-induced structural rearrangement on the basis of cryofracture observation obtained at different times after the preshear imposed.

Cross-Linking of Reactive Lyotropic Liquid Crystals for Nanostructure Retention

In applications requiring nanoscale order, control over the structure formation is critical for appropriate function. Reactive surfactants forming reactive lyotropic liquid crystals (LLC) enable the formation of nanotructured polymers that exhibit enhanced physical properties when the original order is retained after polymerization. In this work, the use of a cross-linker to retain the LLC order for a monomethacrylate quaternary ammonium surfactant monomer in water during polymerization was explored. The cross-linker segregates to the polar regions of the surfactant assembly, likely near the quaternary ammonium group of the reactive surfactant. The use of a cross-linker enables the retention of the original LLC order after polymerization for hexagonal LLC phases that are not retained by other means. Increased polymerization rates are observed at low cross-linker concentrations. At higher cross-linker concentrations, the polymerization rates decrease because of a decrease in LLC order. More regular ordered morphologies are observed for systems that retain the hexagonal LLC order during polymerization. The resulting LLC order is also present after drying and swelling the polymer in water, therefore producing a polymer with robust LLC order. Enhancements in water uptake were also observed for polymers that retain the original order through cross-linking compared to systems that exhibit change in order. This behavior is directly related to the retention of the original LLC order.

Main-chain azo polyaramides with high thermal stability and liquid crystal properties

Two novel main-chain aromatic polyamides containing azobenzene were synthesized by polycondensation of trans-azobenzene-4,4′-dicarbonyl chloride with various aromatic diamines under low temperature. Their molecular structures were identified to be symmetric and regular by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy and elemental analysis. Polymers exhibited not only high thermal stability, but also lyotropic liquid crystal (LC) phases in N,N-dimethylacetamide solution which is due to hydrogen bonding and an ordered rigid structure. The crystal behaviours of the polymers were studied with X-ray diffraction analysis, and the photochromism was investigated with an ultraviolet–visible spectrophotometer with 365 nm ultraviolet irradiation. An abnormal change of the crystal behavior and thermal stability of polymer was found to be related with molecular structure containing ether linkage. The azo polyaramides can be applied in fields of optical techniques and potential photochromics fibres spinning in wide temperature ranges

Aliphatic chain length effects on photopolymerization kinetics and structural evolution of polymerizable lyotropic liquid crystals

Polymerizable lyotropic liquid crystals (LLCs) have the potential advantage of producing materials with anisotropic morphologies and nanometer size dimensions with potential in applications, such as drug delivery, catalysis, and tissue engineering. With the goal of more clearly understanding the factors involved in LLC phase retention after polymerization, this work describes the effect of aliphatic tail length in the amphiphilic molecule on order, polymerization kinetics, and structural evolution of reactive LLC systems. The polymerization kinetics are influenced by the LLC phase morphology with increases in the polymerization rate as the LLC phase increases in order. Enhanced polymerization rates are a result of an apparent increase in the termination and propagation rate parameters, induced by a local increase in monomer concentration due to segregation effects in the LLC phases. Polymerization in hexagonal phases formed from reactive amphiphiles with longer aliphatic tails exhibit lower polymerization rates when compared to systems with shorter aliphatic tails, suggesting that the order of the hexagonal phase decreases as the aliphatic tail increases. Two peaks are observed in the polymerization rate profiles when polymerizing in the hexagonal and cubic phases, with the second peak becoming more pronounced as the aliphatic tail length increases and the order of the LLC phase decreases. This effect appears to be due to changes in morphology during the polymerization process as the hexagonal phase morphology changes significantly during the polymer formation. Different behavior is observed for polymerizations in the lamellar phase for which the LLC phase is retained after polymerization.

Apparent electrocatalysis on 3D nanoporous platinum film electroplated from hexagonal lyotropic liquid crystalline phase of Triton X-100

Electrocatalytic effect of nanoporous interface between platinum (Pt) and electrolyte was investigated in terms of direct electrochemical oxidation of glucose. A Pt film with 3D nanopores was electroplated from the hexagonal (H 1) lyotropic liquid crystal (LLC) phase of t-octylphenoxypolyethoxyethanol (Triton X-100), a nonionic surfactant with a phenyl group in a hydrophobic tail. This Pt film, which was electroplated from H 1-LLC of Triton X-100 (ePt-H 1-TX100), comprised closely stacked crystalline (face centered cubic) nanoparticles (diameter, 4–7 nm) with 3D nanopores (width, 1–2 nm) developed among the particles. The ePt-H 1-TX100 showed high surface roughness and selective enhancement of a sluggish redox reaction, that is, kinetic-controlled reaction such as glucose oxidation. Nonenzymatic glucose sensing can be achieved by using discriminatively enhanced sensitivity to glucose over redox active interfering molecules.

Template electrochemical deposition and characterization of zinc–nickel alloy nanomaterial

Abstract Anodic aluminium oxide and the hexagonal phase of lyotropic liquid crystals containing zinc and nickel ions were used to prepare Zn–Ni alloy nanorods. Highly ordered alloy nanoparticles were obtained by direct electrochemical reduction of zinc and nickel ions from an aqueous solution into the pores of the alumina membrane. The combination of the hexagonal phase of a liquid crystal and the alumina membrane (double template deposition) leads to the reduction of size of the nanorods. Particles that grow from the bottom of the pore of alumina membrane have many subdivisions due to the columns of the liquid crystals. Potentiodynamic stripping of the film confirmed the presence of the alloy phases. Electrochemical impedance spectroscopy analysis reveals the existence of two-separated time constants and the diffusion of lithium ions in the pores of the nanostructured film.

Mechanical and Chemical Protection of a Wired Enzyme Oxygen Cathode by a Cubic Phase Lyotropic Liquid Crystal

When implanted in animals, enzyme-containing battery electrodes, biofuel cell electrodes, and biosensors are often damaged by components of the biological environment. An O2 cathode, superior to the classical platinum cathode, which would be implanted, as part of a caseless physiological pH miniature Zn-O2 battery or as part of a caseless and membraneless miniature glucose-O2 biofuel cell, is rapidly damaged by serum urate at its operating potential. The cathode is made by electrically connecting, or wiring, reaction centers of bilirubin oxidase to carbon with an electron-conducting redox hydrogel. In the physiological pH 7.3 electrolyte battery or biofuel cell, the O2 cathode should operate at, or positive of, 0.3 V (Ag/AgCl), where the urate anion, a common serum component, is electrooxidized. Because an unidentified urate electrooxidation intermediate, formed in the presence of O2, damages the wired bilirubin oxidase electrocatalyst, urate must be excluded from the cathode. Unlike O2, which permeates through both the lipid and the aqueous interconnected networks of cubic-phase lyotropic liquid crystals, urate permeates only through their continuous three-dimensional aqueous channel networks. The aqueous channels have well-defined diameters of approximately 5 nm in the monoolein/water cubic-phase liquid crystal. Through tailoring the wall charge of the aqueous channels, the anion/cation permeability ratio can be modulated. Thus, doping the monoolein of the monoolein/water liquid crystal with 1,2-dioleoyl-sn-glycero-3-phosphate makes the aqueous channel walls anionic and reduces the urate permeation in the liquid crystal. As a result, the ratio of the urate electrooxidation current to the O2 electroreduction current is reduced from 1:3 to 1:100 for 5-mm O2 cathodes rotating at 1000 rpm. Doping with 1,2-dioleoyl-sn-glycero-3-phosphate also increases the shear strength of the cubic-phase monoolein/water lyotropic liquid crystal. While the undoped liquid crystal is promptly damaged at the 0.1 N m-2 average shear stress generated by rotating the 5-mm-diameter disk cathode at 1000 rpm in a physiological aqueous solution, the 10 mol % 1,2-dioleoyl-sn-glycero-3-phosphate-doped film remains intact. The mechanical strengthening of the lyotropic liquid crystal by the two-tailed 1,2-dioleoyl-sn-glycero-3-phosphate is attributed to cross-linking hydrophobic bonds (i.e., bonds resulting of the increase in entropy upon the freeing of the translation and rotation of multiple water molecules), which is analogous to the strengthening of polymer-based plastic materials by cross-linking through covalent bonds.

Application of a Water Soluble Alkoxysilane for the Formation of Mesoporous Silica from Nonionic Surfactant Micelles Bearing Cholesterol

Abstract A water soluble silica precursor, tetrahydroxyethyl orthosilicate (THEOS), was used for the synthesis of mesoporous silica from micellar solutions of a nonionic surfactant bearing cholesterol moiety (ChEO10), which also forms a variety of lyotropic liquid crystal (LLC) structures. The resulting mesoporous silica showed ribbon-like structures, both in μm and nm scale, corresponding to the rectangular LLC phase of ChEO10. We propose the use of THEOS as a novel silica precursor for the investigation of tailored imprinting of LLC topology into the mesoporous silica.

Self-Organization of a Wedge-Shaped Surfactant in Monolayers and Multilayers

The self-organization behavior of a wedge-shaped surfactant, disodium-3,4,5-tris(dodecyloxy)phenylmethylphosphonate, was studied in Langmuir monolayers (at the air-water interface), Langmuir-Blodgett (LB) monolayers and multilayers, and films adsorbed spontaneously from isooctane solution onto a mica substrate (self-assembled films). This compound forms an inverted hexagonal lyotropic liquid crystal phase in the bulk and in thick adsorbed films. Surface pressure isotherm and Brewster angle microscope (BAM) studies of Langmuir monolayers revealed three phases: gas (G), liquid expanded (LE), and liquid condensed (LC). The surface pressure-temperature phase diagram was determined in detail; a triple point was found at approximately 10 degrees C. Atomic force microscope (AFM) images of LB monolayers transferred from various regions of the phase diagram were consistent with the BAM images and indicated that the LE regions are approximately 0.5 nm thinner than the LC regions. AFM images were also obtained of self-assembled films after various adsorption times. For short adsorption times, when monolayer self-assembly was incomplete, the film topography indicated the coexistence of two distinct monolayer phases. The height difference between these two phases was again 0.5 nm, suggesting a correspondence with the LE/LC coexistence observed in the Langmuir monolayers. For longer immersion times, adsorbed multilayers assembled into highly organized periodic arrays of inverse cylindrical micelles. Similar periodic structures, with the same repeat distance of 4.5 nm, were also observed in three-layer LB films. However, the regions of organized periodic structure were much smaller and more poorly correlated in the LB multilayers than in the films adsorbed from solution. Collectively, these observations indicate a high degree of similarity between the molecular organization in Langmuir layers/LB films and adsorbed self-assembled films. In both cases, monolayers progress through an LE phase, into LE/LC coexistence, and finally into LC phase as surface density increases. Following the deposition of an additional bilayer, the film reorganizes to form an array of inverted cylindrical micelles.