Hexagonal Cylinder Research Articles

Self-assembly of copper-free maltoheptaose-block-polystyrene nanostructured thin films in real and reciprocal space

The promising carbohydrate-based block copolymer maltoheptaose-block-polystyrene (MH-b-PS) has been used for high-performance memory transistors and next generation nanolithography. In order to realize the potential of MH-b-PS especially in microelectronic applications, we firstly improved its synthetic method for obtaining large amount of copper-free MH-b-PS. The main improvement relies on the removal of the residual copper catalyst by using a chelating resin. Then, the microphase separation of copper-free MH-b-PS in both thin film and bulk states under different solvent vapor annealing conditions were investigated comprehensively and compared with our previous report by using both real-space and reciprocal-space techniques. A phase transition of MH-b-PS from hexagonal close-packed horizontal cylinders to face-centered cubic were observed when increasing the amount of tetrahydrofuran in the mixture annealing solvent of tetrahydrofuran and H2O. More details about self-assembled MH-b-PS nanostructures were analyzed by comparing grazing incidence small angle X-ray scattering patterns with corresponding atomic force microscopy phase images.

Noise Source Distribution Generated by Longitudinal Vortex on the End Surface of the Hexagonal Cylinder

Noise Source Distribution Generated by Longitudinal Vortex on the End Surface of the Hexagonal Cylinder

Self-organization at the first stage of honeycomb construction: Analysis of an attachment-excavation model.

Honeybees construct nests that consist of regularly arrayed hexagonal cylinders. In the first stage of honeycomb construction, they build a linear sequence of tetrapod structures that form the basis of the comb. However, considering their physiological limitations, it is unknown how honeybees produce that initial pattern. Herein, in an attempt to understand the mechanisms of honeycomb construction, we propose an agent-based model, the attachment-excavation model, in which worker honeybees are classified into attachers who secrete and attach wax, and excavators who excise the attached wax. The model assumes that workers instinctively refrain from digging through the thin parts of a wax cluster. We then conduct two-dimensional (2D) simulations that show how a tripod pattern can be seen as a projection of tetrapods onto a plane. The simulation results show that the tripod pattern emerges due to competition between the attachers and excavators. As time advances, the isotropic wax growth causes the tripods to connect planarly. Because the homogeneously broadened structures do not match that of a natural comb, we employ anisotropic wax growth to obtain a linear sequence of constructed tripods, thus suggesting that anisotropy is a significant contributor to the first stage of honeycomb construction. From our simulation results, we conclude that honeybees utilize self-organization to achieve complexity during the first stage of honeycomb construction. It is anticipated that the results of our study will provide insights into how complexity can be achieved within a hierarchy.

2D Metal Chalcogenide Nanopatterns by Block Copolymer Lithography

AbstractNanoscale structure engineering is in high demand for various applications of 2D transition metal dichalcogenides (TMDs). An edge‐exposed 2D polycrystalline MoS2 nanomesh thin film is demonstrated via block copolymer (BCP) nanopatterning. Molybdenum nanomesh structure is formed by direct metal deposition of hexagonal cylinder BCP nanotemplate and the following lift‐off process. Subsequent sulfurization of the molybdenum nanomesh creates MoS2 nanomesh thin films without any degradative etching step. The approach is applicable to not only other metal sulfides and oxides but also other nanoscale structures of TMD thin films including nanodot and nanowire array by means of various BCP nanotemplate shapes. As the edge site of MoS2 is highly active for NO2 sensing, the edge‐exposed MoS2 nanomesh demonstrates sevenfold enhancement of sensitivity for NO2 molecules compared to uniform thin film as well as superior reversibility even under 80% relative humidity environment. This structure engineering method could greatly strengthen the potential application of 2D TMD materials with the optimal customized nanoscale structures.

Modelling of flow around hexagonal and textured cylinders

The flow regime around a hexagonal polygon with low Reynolds numbers Re < 200 is numerically investigated in two different orientations namely face- and corner oriented. The basic flow characteristics, including drag coefficient, lift coefficient, Strouhal number and critical Reynolds number of the hexagonal cylinders, are calculated by solving the Navier–Stokes and mass conservation (continuity) equations, using the Simple (semi-implicit method for pressure-linked equations) algorithm. Within the studied range of Re, the predicted lift coefficient and Strouhal number of the face-oriented hexagon were higher than those of the corner-oriented hexagon. In contrast, the predicted drag coefficient and critical Reynolds number of the corner-oriented hexagon were greater than those of the face-oriented one. Flow characteristics of a novel textured geometry are also studied using three-dimensional transient analysis. The Strouhal number St of the textured geometry was found to be in between the St of both the hexagonal cylinders, and its lift coefficient is lower than that of the hexagonal cylinders. The computational fluid dynamics results show that, within the studied Reynolds number range, the drag coefficient of the textured pipe is almost equal to that of the circular cylinder while its lift coefficient is substantially smaller than that of circular and face- and corner-oriented hexagon pipes.

Controlled Synthesis of Organic Frameworks of Pillar[6]Arene By Electrochemical Oxidation

Recently, the novel synthesis of supramolecular 2D sheet materials composed of a pillar[6]arene (a cyclic hexamer of p-arylenemethylene), driven by charge-transfer (CT) interaction between its hydroquinone form and its benzoquinone form was reported [1]. When the hydroquinone form of pillar[6]arene was oxidized with an oxidant in a methanol solution, a generated partially oxidized benzoquinone form underwent CT complex formation with its pristine form to 2D-assemble with a hexagonal packing, followed by further assembly to form fibrils. In order to control the size and shape of the material, we investigated the electrochemical oxidation of a pillar[6]arene, and resulted in the successful formation of uniform hexagonal cylinder structures on an electrode surface (Figure 1) [2]. [1] T. Ogoshi, K. Yoshikoshi, R. Sueto, H. Nishihara, T. Yamagishi, Angew. Chem. Int. Ed. 2015, 54, 6466-6469. [2] C. Tsuneishi, Y. Koizumi, R. Sueto, H. Nishiyama, K. Yasuhara, T. Yamagishi, T. Ogoshi, I. Tomita, S. Inagi, Chem. Commun. 2017, 53, 7454-7456. Figure 1

Low weight additive manufacturing FBG accelerometer: Design, characterization and testing

Structural Health Monitoring is considered the process of damage detection and structural characterization by any type of on-board sensors. Fibre Bragg Gratings (FBG) are increasing their popularity due to their many advantages like easy multiplexing, negligible weight and size, high sensitivity, inert to electromagnetic fields, etc. FBGs allow obtaining directly strain and temperature, and other magnitudes can also be measured by the adaptation of the Bragg condition. In particular, the acceleration is of special importance for dynamic analysis. In this work, a low weight accelerometer has been developed using a FBG. It consists in a hexagonal lattice hollow cylinder designed with a resonance frequency above 500 Hz. A Finite Element Model (FEM) was used to analyse dynamic behaviour of the sensor. Then, it was modelled in a CAD software and exported to additive manufacturing machines. Finally, a characterization test campaign was carried out obtaining a sensitivity of 19.65 pm/g. As a case study, this paper presents the experimental modal analysis of the wing of an Unmanned Aerial Vehicle. The measurements from piezoelectric, MEMS accelerometers, embedded FBGs sensors and the developed FBG accelerometer are compared.

Hierarchical Self-Organization of AB n Dendron-like Molecules into a Supramolecular Lattice Sequence.

To understand the hierarchical self-organization behaviors of soft materials as well as their dependence on molecular geometry, a series of ABn dendron-like molecules based on polyhedral oligomeric silsesquioxane (POSS) nanoparticles were designed and synthesized. The apex of these molecules is a hydrophilic POSS cage with 14 hydroxyl groups (denoted DPOSS). At its periphery, there are different numbers (n = 1–8) of hydrophobic POSS cages with seven isobutyl groups (denoted BPOSS), connected to the apical DPOSS via flexible dendron type linker(s). By varying the BPOSS number from one to seven, a supramolecular lattice formation sequence ranging from lamella (DPOSS-BPOSS), double gyroid (space group of Ia3̅d, DPOSS-BPOSS2), hexagonal cylinder (plane group of P6mm, DPOSS-BPOSS3), Frank–Kasper A15 (space group of Pm3̅n, DPOSS-BPOSS4, DPOSS-BPOSS5, and DPOSS-BPOSS6), to Frank–Kasper sigma (space group of P42/mnm, DPOSS-BPOSS7) phases can be observed. The nanostructure formations in this series of ABn dendron-like molecules are mainly directed by the molecular geometric shapes. Furthermore, within each spherical motif, the spherical core consists hydrophilic DPOSS cages with flexible linkages, while the hydrophobic BPOSS cages form the relative rigid shell, and contact with neighbors to provide decreased interfaces among the spherical motifs for constructing final polyhedral motifs in these Frank–Kasper lattices. This study provides the design principle of molecules with specific geometric shapes and functional groups to achieve anticipated structures and macroscopic properties.

Numerical simulation of flow and heat transfer around hexagonal cylinder

Numerical simulation of flow and heat transfer around hexagonal cylinder

Nanopattern transformation of ABC triblock copolymer thin films induced by strong solvent selectivity and annealing

Nanopattern transformation behaviors of polyisoprene-block-polystyrene-block-poly(2-vinylpyridine) (PI-b-PS-b-P2VP) asymmetric ABC triblock copolymer were investigated systematically with various control parameters, including different solvents for polymer solution and annealing conditions in this paper. Ordered nanopattern of PI-b-PS-b-P2VP with hexagonal cylinders could be obtained when PI-b-PS-b-P2VP toluene solution was spin-coated on silicon substrate followed by toluene vapor annealing process. When the film with hexagonal and cylindrical nanopattern was exposed to saturated toluene vapor, the order-order transition of cylindrical nanopattern to parallel nanopattern was observed due to the strong selectivity of toluene to PS and PI blocks. Furthermore, fingerprint nanopattern could also be obtained by solvent annealing in tetrahydrofuran vapor. The nanopattern transformation was due to different selectivity of solvents and incompatibilities of the three blocks of PI-b-PS-b-P2VP under various solvent annealing conditions.

Precision Synthesis and Distinct Assembly of Double-Chain Giant Surfactant Regioisomers

The delicate influence of minute structural difference, such as regiochemistry, on self-assembly and phase behaviors has been commonly observed in small molecules but rarely in synthetic polymers. Herein, we report the precision synthesis of a series of double-chain giant surfactant regioisomers and their distinct phase structures and phase behaviors. These giant surfactants possess a hydroxyl-functionalized cubic T8 polyhedral oligomeric silsesquioxane head and two polystyrene tails tethered at para-, meta-, and ortho-configurations and were prepared following the sequential “click” method. As revealed by temperature-dependent small-angle X-ray scattering and bright-field transmission electron microscopy, their order–disorder transition temperatures decrease in the order of ortho-, meta-, and para-isomers, while order–order transitions were observed in the meta-isomer from lamellae to double gyroids and in the ortho-isomer from double gyroids to hexagonal cylinders upon increasing temperature. The mechan...

Films of Reduced Graphene Oxide with Metal Oxide Nanoparticles Formed at a Liquid/Liquid Interface as Reusable Surface Enhanced Raman Scattering Substrates for Dyes.

Free standing, thin films of reduced graphene oxide (rGO) with ZnO, CuO and SnO(2) nanostructures are prepared at a water/toluene interface utilizing simple interfacial reaction and self-assembly. rGO-ZnO, rGO-CuO and rGO-SnO(2) films exhibit unique morphologies such as hexagonal cylinders, elongated splinters, and balls, respectively, wrapped by rGO layers. The hybrid films exhibit surface enhanced Raman scattering (SERS) of rhodamine 6G dye with enhancement factors one order higher than bare metal oxide caused by a synergic effect of charge transfer between the dye, metal oxide and rGO. Doping with Ag+ ions improves SERS enhancement in rGO-Ag–ZnO hybrid films, exploiting the electromagnetic effect of metal surface plasmons. Detection sensitivity up to 10 μM dye with an enhancement factor of 104 is shown. The enhanced photodegradation rate by the hybrid films is utilized for UV induced regeneration of the used SERS substrate and is demonstrated for successive use of different analytes.

Tunable quasi-monochromatic near-field radiative heat transfer in s and p polarizations by a hyperbolic metamaterial layer

The spectra of thermal radiation have been controlled for thermophotovoltaics and mid-infrared light sources, and the spectral heat flux has been shown to exceed the blackbody limit by utilizing near-field coupling. We show that a hyperbolic metamaterial layer enables quasi-monochromatic near-field radiative heat transfer between a metallic emitter and a dielectric receiver. The quasi-monochromatic transfer originates from the Fabry-Perot resonance in the hyperbolic layer, where evanescent waves in the vacuum gap become propagative. The Fabry-Perot resonance is excited in s and p polarizations, and the resonant condition is almost independent of the lateral wavenumber due to the large effective parallel permittivity of the hyperbolic metamaterial. The resonant frequency is tuned by the volume filling fraction and the thickness of the layer, while the frequency misalignment between polarizations is kept small. Furthermore, the resonant frequency is shown to be robust to the fluctuation of the gap width and the refractive index of the receiver dielectrics. The hyperbolic metamaterial layer is applied to near-field thermophotovoltaic energy generation, and both the power output and the efficiency are enhanced simultaneously. Numerical simulation reveals that the hyperbolic metamaterial layer can be realized by a hexagonal cylinder array.

Lattice Boltzmann Simulation of Natural Convection in an Annulus between a Hexagonal Cylinder and a Square Enclosure

Laminar natural convection in a water filled square enclosure containing at its center a horizontal hexagonal cylinder is studied by the lattice Boltzmann method. The hexagonal cylinder is heated while the walls of the cavity are maintained at the same cold temperature. Two orientations are treated, corresponding to two opposite sides of the hexagonal cross-section which are horizontal (case I) or vertical (case II). For each case, the results are presented in terms of streamlines, isotherms, local and average convective heat transfers as a function of the dimensionless size of the hexagonal cylinder cross-section (0.1≤B≤0.4), and the Rayleigh number (103≤Ra≤106).

Vortex shedding control on a bare cylinder using hexagonal perforated outer cylinder

The aim of the study is to observe the effect of outer hexagonal perforated cylinder surrounding an inner cylinder on vortex structure behind bluff body. Vortex shedding characteristics from bluff body are experimentally studied by particle image velocimetry (PIV) in deep water. The inner cylinder had seven different diameters (Di), varied from 30 to 90 mm with an increment of 10 mm and the hexagonally perforated outer cylinder placed outside of the inner cylinder was used as a control element. Experiments were carried out with six perforated cylinders with a diameters of 100 mm (Do) and six porosities, β, with hole diameter 10 mm. The porosity, β, and diameter ratio, Di/Do, had substantial effect on the flow characteristics behind the cylinder. For the range of diameter ratios of 0.3 ≤ Di/Do≤ 0.5 the optimum porosity that controls the flow structure is found to be β = 0.6. For 0.6 ≤ Di/Do≤ 0.7 it is β = 0.5 and β = 0.4 for 0.8 ≤ Di/Do≤ 0.9. With increasing diameter ratio, Di/Do, peak magnitude locations of Reynolds shear stress, [Formula: see text], and turbulence kinetic energy approach the inner outer cylinder system slightly. For all diameter ratios, β = 0.6 is the most effective porosity ratio.

Progesterone solubilization within reverse hexagonal mesophase

The present work reports on the preparation and characterization of progesterone-loaded reverse hexagonal (HII) mesophase based on a glycerol monooleate (GMO)/tricaprylin (TAG)/water mixture for transdermal application.Several compositions into which progesterone was quantitatively solubilized were selected and used in the present study in order to evaluate the effect of the hormone on structural transitions and characteristics.A GMO/TAG of 90:1wt ratio with 20wt% water was found to form HII mesophases with relative high solubilization capacity of 4wt% progesterone and a shelf life of over one year. The structures were identified by cross-polarized light microscopy (CPLM). Structural confirmations were obtained from small-angle X-ray scattering (SAXS) measurements. The hormone is solubilized at the interface of the HII mesophase as confirmed by SAXS, rheology, FTIR, and DSC. The progesterone, which is loaded onto reverse hexagonal cylinders, leads to strengthening the hydrogen bonding and to better packing of the HII mesophase, suggesting that progesterone is a kosmotropic agent.The reverse hexagonal mesophase seems to be a promising carrier for solubilization of progesterone.

Graft-through Synthesis and Assembly of Janus Bottlebrush Polymers from A-Branch-B Diblock Macromonomers.

We report the synthesis of Janus bottlebrush block copolymers by graft-through polymerization of branched diblock macromonomers. Self-assembly of the bottlebrushes was characterized by small-angle X-ray scattering, atomic force microscopy, and scanning electron microscopy. Phase separation and packing models of the bottlebrushes were computed, and their self-assembly behavior was corroborated experimentally in bulk and in thin films. Lamellar, hexagonal cylinder, and gyroid phases were observed and modeled. The A-branch-B Janus bottlebrush structure provides several unique advantages in the context of bottlebrush polymer assembly, including access to the first examples of gyroid phases.

Synchrotron X-ray scattering and photon correlation spectroscopy studies on thin film morphology details and structural changes of an amorphous-crystalline brush diblock copolymer

Abstract We investigated structural details and temperature-induced structural changes of an amorphous-crystalline brush diblock copolymer, poly(3-((6-((7-(9H-carbazol-9-yl)heptanoyl)oxy)hexyl)thio)propyl glycidyl ether) 60 - b -poly(glycidyl 12-((3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl)oxy)-12-oxododecanoate) 20 (PGK 60 -PGF 20 ) in nanoscale thin films using synchrotron grazing incidence X-ray scattering (GIXS) and X-ray photon correlation spectroscopy (XPCS). Interestingly, the diblock copolymer was found to form a mixture of two different hexagonal cylinder structures (HEX1 and HEX2) where the PGF cylinders were aligned in the film plane. HEX1 was composed of PGF cylinders with higher population of crystals while HEX2 consisted of PGF cylinders with lower population of crystals. Surprisingly, the PGF block chains favorably self-assembled because of strong lateral interactions in the bristles, forming vertical multibilayer structure with partial interdigitation even in the highly confined cylindrical geometry. In heating run up to 340 K, some fraction of HEX2 was transformed to HEX1 via cold crystallization. In contrast, HEX1 was transformed to HEX2 above 340 K because of melting of the PGF crystals. The XPCS analysis found that the HEX structural changes associated with the cold crystallization in the PGF cylinder domains took place with relatively fast dynamics. The HEX structural changes associated with melting of the PGF crystals in the cylinder domains occurred with relatively slow dynamics; this unusual dynamics of structural changes might be attributed to a high energy melting process of PGF crystals against strong lateral interactions of the bristles.

Iterative Exponential Growth Synthesis and Assembly of Uniform Diblock Copolymers.

Studies on the phase segregation of unimolecular block copolymers (BCPs) are limited by a lack of reliable, versatile methods for the synthesis of such polymers on the preparative scale. Herein, we describe an advancement of Iterative Exponential Growth (IEG) wherein chiral allyl-based IEG oligomers are subjected to thiol-ene reactions and converted into unimolecular BCPs. With this strategy we have synthesized uniform BCPs with molar masses up to 12.1 kDa on ∼1 g scale. BCPs composed of decane-based side chains and either triethyleneglycol- or thioglycerol-based side chains phase-segregate into hexagonal cylinder morphologies. The assembly is not driven by side-chain crystallization, but is instead the result of amorphous BCP assembly.

Effect of Geometrical Asymmetry on the Phase Behavior of Rod-Coil Diblock Copolymers.

The effect of geometrical asymmetry β (described by the length-diameter ratio of rods) on the rod-coil diblock copolymer phase behavior is studied by implementation of self-consistent field theory (SCFT) in three-dimensional (3D) position space while considering the rod orientation on the spherical surface. The phase diagrams at different geometrical asymmetry show that the aspect ratio of rods β influences not only the order-disorder transition (ODT) but also the order-order transition (OOT). By exploring the phase diagram with interactions between rods and coils plotted against β, the β effect on the phase diagram is similar to the copolymer composition f. This suggests that non-lamellae structures can be obtained by tuning β, besides f. When the rods are slim compared with the isotropic shape of the coil segment (β is relatively large), the phase behavior is quite different from that of coil-coil diblock copolymers. In this case, only hexagonal cylinders with the coil at the convex side of the interface and lamella phases are stable even in the absence of orientational interaction between rods. The phase diagram is no longer symmetrical about the symmetric copolymer composition and cylinder phases occupy the large area of the phase diagram. The ODT is much lower than that of the coil-coil diblock copolymer system and the triple point at which disordered, cylinder and lamella phases coexist in equilibrium is located at rod composition fR = 0.66. In contrast, when the rods are short and stumpy (β is smaller), the stretching entropy cost of coils can be alleviated and the phase behavior is similar to coil-coil diblocks. Therefore, the hexagonal cylinder phase formed by coils is also found beside the former two structures. Moreover, the ODT may even become a little higher than that of the coil-coil diblock copolymers due to the large interfacial area per chain provided by the stumpy rods, thus compensating the stretching entropy loss of the coils.