Two-dimensional Hexagonal Phase Research Articles

High-resolution structural elucidation of extremely swollen lyotropic phases

Self-assembled lyotropic phases are important in a variety of applications, in particular microemulsions are essential for formulation science. A spectacular situation arises when microemulsions are made to swell by systematically increasing the bending modulus of the surfactant film separating the oil and water regions. In an attempt to realize such extremely swollen microemulsion phases, Peter et al. [Phys. Rev. Lett., 76 (1996) 3866] found a variety of lyotropic phases including a long-range ordered three-dimensional cubic phase over a narrow section of the complex phase diagram of a pseudo-quaternary system composed of decane, brine, octanol, and sodium dodecyl sulfate. In this work, the same region of the phase diagram was reinvestigated using high-resolution small-angle X-ray scattering (HR-SAXS) and rheo-SAXS, which is an important technical aspect for homogenizing the sample and orienting the structural units. Whilst the formation of a swollen two-dimensional hexagonal phase was observed, the structural features of a cubic phase were not detected. The long correlation lengths noted prior were also seen here, over 2000 nm for the hexagonal phase, taken from rheo-SAXS measurements. Based on the measurements covering more than three orders of magnitude in scattering vector, the structure appeared to be an organization of elongated swollen emulsion droplets, which could form an interconnected structure, dense liquid-like order, or further order into a hexagonal morphology with unusually large lattice spacings for a surfactant system.

Structure and stoichiometry of CTAB-DNA complexes.

We have studied the structure of cetyltrimethylammonium bromide-DNA complexes using small angle x-ray diffraction and elemental analysis. These complexes exhibit a two-dimensional hexagonal phase. The diffraction data have been analyzed using electron density models based on two different structures of these complexes proposed in the literature, which differ in the micelle to DNA stoichiometry. The structure with a 1:2 micelle-DNA stoichiometry is found to be more consistent with the diffraction data. Furthermore, this structure is also supported by the stoichiometry deduced from elemental analysis. Madelung energies of the two structures, calculated from the electrostatic interaction between their cylindrical constituents, give insight into their relative stability.

Synthesis of ZnO nanoparticles supported on mesoporous SBA-15 with coordination effect -assist for anti-bacterial assessment

Polyethyleneimine (PEI) was immobilized on SBA-15 for obtaining polyethyleneimine-modified silica PEI@SBA-15s (PEI@SBA-1.0, PEI@SBA-1.5, and PEI@SBA-2.0). With the coordination from PEI, zinc ions were impregnated on the PEI@SBA-15s, and then, Zn2+-PEI@SBA-15s were calcined at 550 ℃ to obtain the nano zinc oxide loaded on the mesoporous silica, ZnO-SBA-15s (ZnO-SBA-1.0, ZnO-SBA-1.5, and ZnO-SBA-2.0). The anti-bacterial activity of ZnO-loaded SBA-15 was; thereafter, assessed by the zone of inhibition and enzyme labeling methods. The results confirmed that the coordination ability of the imino groups in PEI helped adsorb more zinc ions during the process of impregnation so that more nano-ZnO could be supported on the surface of SBA-15. The modification did not change the mesostructure of the two-dimensional hexagonal phase and orderliness of SBA-15. At the mass ratio of PEI:SBA-15 = 1.0:1, 1.5:1, and 2.0:1, the concentration of zinc element (wt.%) was measured by inductively coupled plasma optical emission spectrometry as 2.5, 2.56, and 3.5% for ZnO-SBA-1.0, ZnO-SBA-1.5, and ZnO-SBA-2.0, respectively. The size of inhibition of SBA-15, ZnO-SBA-0, ZnO-SBA-1.0, ZnO-SBA-1.5, and ZnO-SBA-2.0 were 0, 1.14 ± 0.01, 2.56 ± 0.01, 2.58 ± 0.01, and 2.69 ± 0.02 cm, respectively. ZnO-SBA-15s suppressed the growth of Escherichia coli compared to blank SBA-15 in a ZnO dose-dependent manner.

A study of two-dimensional hexagonal phase array grating in MgO:LN based on the Talbot effect

In this paper, theoretical researches on the MgO:LN tunable hexagonal phase array grating based on the Talbot effect were presented. Researches revealed the effects on the intensity distribution of near-field diffraction from array grating duty cycle which is defined as D, phase difference which is defined as Δφ and the distance coefficient which is defined as β. The results obtained show that good near-field diffraction images can be achieved at D=52%, Δφ=0.75π, β=0.2. Based on the theoretical researches, the tunable hexagonal phase array grating is designed and fabricated from periodically poled MgO:LN crystal. Through experimental test, the Talbot effect diffraction imaging map is successfully obtained at different Δφ and β, which verifies the results of the theoretical researches.

Embedding DNA in surfactant mesophases: The phase diagram of the ternary system dodecyltrimethylammonium–DNA/monoolein/water in comparison to the DNA-free analogue

The self-assembly of a true ternary mixture comprising an electroneutral complex of DNA anions and surfactant cations (dodecyltrimethylammonium cations, DTA), water, and nonionic surfactant (monoolein, MO) has been studied. The phase diagrams of two systems, DTA–DNA/MO/water and, for comparison, dodecyltrimethylammonium bromide (DTAB)/MO/water, were obtained by visual inspection, microscopic examination under polarized light, small-angle X-ray scattering (SAXS) and deuterium NMR (2H NMR) at 298K and normal pressure. The isothermal phase diagram of the DTA–DNA/MO/water system contains four liquid crystalline (LC) phase regions (reversed hexagonal, Pn3m, Ia3d, lamellar). The supramolecular assemblies evolve from a bicontinuous cubic structure of the reversed type to the two-dimensional hexagonal phase as the content of DTA–DNA is increased. While DTA–DNA tends to form a reversed hexagonal phase, DTAB is incorporated into the existing lamellar phase formed by MO and water giving rise to swelling and to significant extension of the lamellar phase region. There is only a small tendency of the cubic phases existing in the binary system MO/water to accommodate DTAB or DTA–DNA.

Three-dimensional periodic complex structures in soft matter: investigation using scattering methods.

Three-dimensional periodic complex structures are encountered in various soft matter systems such as liquid crystals, block-copolymer phases and the related nano-structured materials. Here, we review several well-defined topologies: two-dimensional hexagonal phase, three-dimensional packing of spheres, tetrahedral close packing (tcp) bi-continuous and tri-continuous cubic phases. We illustrate how small-angle X-ray scattering experiments help us to investigate these different structures and introduce the main available structural models based on both direct and inverse methods.

Linear and nonlinear optical properties of Au/SiO2 nanocomposite prepared by P123

Mesoporous silica thin films loaded with gold nanoparticles are synthesized in the presence of EO20PO70EO20 (P123). Transmission electron microscope images show that the matrix of the nanocomposite is an ordered porous structure with a two-dimensional hexagonal phase. The wide-angle X-ray diffraction pattern implies that the nanocomposite contains gold crystals. These metallic nanoparticle-embedded solid thin films show some linear and nonlinear optical properties due to their special structure and composition. Gold nanoparticles bring about surface plasmon resonance, and an absorption peak stemming from this effect has been observed. The linear absorption property is analyzed by a quantum mechanism, and the results show that it is in°uenced by the size and volume fraction of gold nanoparticles. Furthermore, it shows an obviously clear nonlinear optical property measured by the z -scan technique. The magnitude of the nonlinear refractive index of the nanocomposite is estimated to be about 10^{-10} cm2/W.

A study of two-dimensional hexagonal phase array optical beam splitter modulated by external electric field

In this paper, we establish a theoretical model of reciprocal-lattice vector of the two-dimensional hexagonal phase array optical beam splitter modulated by an external electric field, perform the analysis of the tunable phase-difference array optical beam splitter according to the numerical simulation, and then obtain the images of intensity distribution with different values of fractional Talbot distance and external electric field. The two-dimensional hexagonal phase array optical beam splitter is designed and fabricated by lithium niobate. An experimental study of beam splitting is also given. When the applied voltage is 0.5 kV (with electric field of 1 kV/mm), we observe the phenomenon of the beam splitting in Talbot diffraction. As the external field increases, the images of beam splitting in diffraction become clearer, the experimental results are in agreement with theoretical results.

The theoretical study and numerical simulation of the tunable two-dimensional hexagonal phase array based on Talbot effect

In this paper, on the basis of Talbot effect and using numerical simulation, we analyzed the two-dimensional amplitude and fixed- phase-difference arrays and found that these arrays can easily be affected by temperature, and the intensity distribution at z position behind them can’t be tuned. To solve the problem, an external electric field is used to tune the phase-difference of the phase array. We derived a theoretical model which realizes uniform distribution of light intensity via the application of an external electric field to tune the phase-difference, and the model agreed with Paturzo’s experimental results. The result make a good foundation for the research of new kinds of arrays.

New insights into the initial steps of the formation of SBA-15 materials: an in situ small angle neutron scattering investigation

Time-resolved in situ SANS investigations have provided direct experimental evidence for the three initial steps in the formation of the SBA-15 mesoporous material: an induction period is followed by a shape transformation of the micelles from spherical to cylindrical ones followed by the precipitation of a two-dimensional hexagonal phase.

Tunable two-dimensional hexagonal phase array in domain-engineered Z-cut lithium niobate crystal

An optical phase array with tunable phase step is demonstrated. The phase array consists of a two-dimensional hexagonal lattice of inverted ferroelectric domains fabricated on a Z-cut lithium niobate substrate. The electro-optically tunable phase step is obtained by the application of an external electric field along the z axis of the crystal via transparent electrodes. Theoretical analysis and experimental results are presented, showing that a tunable and flexible adaptive optical illuminator device can be realized by combining the electro-optic tunability with the Talbot effect. Generation of a multiplicity of light patterns is shown.

Are liquid crystalline properties of nucleosomes involved in chromosome structure and dynamics?

Nucleosome core particles correspond to the structural units of eukaryotic chromatin. They are charged colloids, 101 Angstrom in diameter and 55 Angstrom in length, formed by the coiling of a 146/147 bp DNA fragment (50 nm) around the histone protein octamer. Solutions of these particles can be concentrated, under osmotic pressure, up to the concentrations found in the nuclei of living cells. In the presence of monovalent cations (Na(+)), nucleosomes self-assemble into crystalline or liquid crystalline phases. A lamello-columnar phase is observed at 'low salt' concentrations, while a two-dimensional hexagonal phase and a three-dimensional quasi-hexagonal phase form at 'high salt' concentrations. We followed the formation of these phases from the dilute isotropic solutions to the ordered phases by combining cryoelectron microscopy and X-ray diffraction analyses. The phase diagram is presented as a function of the monovalent salt concentration and applied osmotic pressure. An alternative method to condense nucleosomes is to induce their aggregation upon addition of divalent or multivalent cations (Mg(2+), spermidine(3+) and spermine(4+)). Ordered phases are also found in the aggregates. We also discuss whether these condensed phases of nucleosomes may be relevant from a biological point of view.

Dynamics of Guanosine Self-Assembled Aggregates in the Hexagonal Columnar Phase by Quasielastic Neutron Scattering

Abstract Guanosine, one component of the nucleic acids, presents a simple model system to study the self-assembling process and the properties of columnar liquid-crystalline phases. In a recent x-ray study we investigated the structure of the aggregates at medium concentrations and explored the phase-diagram as a function of salt concentration in the solution. A microscopic model has been presented describing the size and distribution of the rod-shaped aggregates consisting of stacked guanosine tetramers. Here we present a first study of the dynamics of guanosine in the two-dimensional hexagonal phase. Inelastic neutron scattering gives further evidence for the “persistent-flexible-hard-rod” model; displacements in the hexagonal plane are found to be extremely high. To a detection limit of 0.04 meV we find no evidence for propagating phonon modes. The quasielastic signal measured is attributed to relaxational motions that is extremely overdamped motions of the guanosine rods.

Structure and morphology of Langmuir-Blodgett films of rod-like poly(phthalocyaninato germoxane)s, studied by transmission electron microscopy

The domain structures and molecular orientation in Langmuir-Blodgett mono-, double and multilayers of rod-like poly(pthalocyaninato germoxane)s with dodecyloxycarbonyl side-chains deposited onto a carbon film substrate are directly visualized using electron diffraction (ED), as well as bright-field (BF) and dark-field (DF) imaging. The ED patterns show an oriented intramolecular spacing of 0.37 nm from the axially stacked phthalocyaninato rings, aligned along the dipping direction and an orthogonally oriented intermolecular spacing of 3.4 nm, arising from parallel packing of rod-like molecules parallel to the layer plane. In addition, arched ( hk0)-type reflections arise from about 40% of the film area of a single monolayer, indicating an end-on orientation of the rod-like molecules relative to the layer plane. In multilayer films, a two-dimensional hexagonal phase and a less ordered layer state with no registration between the molecules in adjacent layers coexist, and the portion of molecules oriented preferentially normal to the layer significantly decreases. The BF images of the monolayers and double layers show a mosaic-like structure, with darker band-like regions about 50 nm in size surrounding brighter mosaic pieces about 300 nm in size. The DF images confirm that the darker regions in the BF image mainly arise as a result of scattering from the 0.37 nm reflection, indicating that the rod-like molecules are oriented parallel to the layer plane. High resolution electron microscopy images taken from the monolayer films show patches of parallel fringes, directly visualizing the lateral 3.4 nm packing of the rods. The fringe regions exhibit a broad orientational distribution about the dipping direction.

The lyotropic liquid crystal properties of n-octyl 1- O-β- d-glucopyranoside and related n-alkyl pyranosides

X-ray diffraction patterns have been obtained for the lyotropic phases of n-octyl 1- O-β- d-glucopyranoside and the related n-heptyl, n-nonyl and n-decyl compounds with water. The octyl compound exhibits all three liquid crystal phases and forms a micellar solution with increasing solvation, when the crystal come into contact with water at room temperature. The X-ray diffraction patterns show a one-dimensional lamellar phase with 〈 d x〉 = 28.4 Å, a three-dimensional face-centered cubic phase with 〈 a〉 = 51.2 Å, and a two-dimensional hexagonal phase with 〈 a〉 = 〈 b〉= 36.7 Å. The micellar solution has a distribution pattern with a maximum at 〈 d x〉 = 33.8 Å. Crystals of the heptyl, nonyl and decyl derivatives form only the lamellar phases and the micellar solution on contact with water at room temperature.