Hexagonal Cylinder Structure Research Articles

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

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.

Mesoporous silicas templated by symmetrical multiblock copolymers through evaporation-induced self-assembly

In this study, we synthesized long-range-ordered mesoporous silicas through evaporation-induced self-assembly (EISA), templated by the ABA-type triblock copolymer PEO-PPO-PEO (F127), and found that the morphologies of the mesostructures could be controlled from a hexagonal cylinder structure to a body-centered cubic (bcc) structure by varying the amount of added tetraethyl orthosilicate (TEOS). In addition, we synthesized the multiblock ABCBA-type copolymer PCL-PEO-PPO-PEO-PCL (PCL-F127-PCL) through ring-opening polymerization (using F127 as the macro-initiator) and then examined the effect of its PCL segments on the morphology of the resulting mesoporous silica. We employed small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and N2 adsorption/desorption isotherms to investigate the mesophase transformations of these mesoporous nanostructures containing various TEOS contents. Upon increasing the molecular weight of the PCL segments, the d-spacing decreased initially, but then increased thereafter. The PCL-F127-PCL multiblock copolymer assembled into an “m”-shaped structure, with the hydrophilic PEO segments folded outside and the hydrophobic PCL and PPO segments aggregated inside. In addition to the relatively strong interactions with the PCL segments, the hydrophilic PPO segments also interacted relatively strongly with the silica matrix, such that some of the PPO segments could enter within it. Using this approach with ABA-type triblock and ABCBA-type multiblock copolymers as templates, we can prepare highly ordered mesoporous silicas having narrow pore size distributions and various mesoporous structures.

Phase Behavior and Conductivity of Sulfonated Block Copolymers Containing Heterocyclic Diazole-Based Ionic Liquids

We have investigated morphologies and conductivities of ionic liquids (ILs) incorporated poly(styrenesulfonate-b-methylbutylene) (PSS-b-PMB) block copolymers by varying kinds of heterocyclic diazoles in ILs. A low molecular weight PSS-b-PMB copolymer (3.5–3.1 kg/mol) with sulfonation level of 17 mol % was employed as a matrix polymer, which indicates disordered morphology at entire temperature examined. The addition of different ILs results in the emergence of various ordered morphologies such as lamellar, hexagonal cylinder, and gyroid structures. Interestingly, it has been revealed that ring structures and alkyl substituents in diazoles play an important role in determining the morphologies of ILs impregnated PSS-b-PMB copolymers, attributed to the dissimilar strength of ionic interaction. Heating the ILs doped PSS-b-PMB copolymers causes intriguing thermoreversible order–order and order–disorder phase transitions, which can be rationalized by classical block copolymer thermodynamics. From conductivity measurements, it has been found that the enhanced conductivity could be achieved by increasing number of protic sites in heterocyclic diazoles. Upon exploring morphology effects on conductivities of ILs-containing PSS-b-PMB copolymers, with decoupled segmental motion of polymer chains and ion transport, similar morphology factor of 0.4 has determined if the morphologies are appeared to be lamellar and/or hexagonal cylinder structures. In contrast, the gyroid-forming sample revealed apparently high morphology factor in the range of 0.6 to 0.7, which is intimately related to better connectivity of ionic channels along cocontinuous PSS phases.

Use of layered double hydroxides to improve the triple phase boundary in anion-exchange membrane fuel cells

We propose a novel approach that uses a positively charged inorganic compound, layered double hydroxide (LDH), as an anion conductor in anion-exchange membrane fuel cells to improve the triple phase boundary (TPB) of catalyst layers. Pt/C catalyst layers with hydrothermally prepared Mg–Al- and Ni–Al-based LDHs (MgAl-LDH and NiAl-LDH, respectively) were constructed, and their oxygen-reduction currents were evaluated under the same conditions as in anion-exchange membrane fuel cells. Scanning electron microscopy and a surface-area analysis revealed that the two LDHs had almost the same surface-area, size, and hexagonal cylinder structure. In contrast, electrochemical measurements showed that MgAl-LDH improved the current densities while NiAl-LDH showed the same current densities as the catalyst layer with no LDHs. These results suggest that MgAl-LDH introduced OH −-conducting paths within the catalyst layers and effectively increased the TPB region in anion-exchange membrane fuel cells.

Phase Transitions in Thin Films of a Diblock Copolymer Composed of a Linear Polymer Block and a Brush Polymer Block with Mesogenic Oligothiophenyl Bristles

In this study, we quantitatively investigated the temperature-dependent phase transition behaviors in thin films of an interesting semirod−coil diblock copolymer, poly(styrene)-b-poly(oligothiophene side chain modified isoprene) (PS-b-POTI), and the resulting morphological structures using synchrotron grazing incidence X-ray scattering combined with differential scanning calorimetry. These analyses provided detailed information about the morphologies of the phase-separated domains and the molecular structures formed in each domain. At room temperature, the diblock copolymer molecules in thin films were found to form an alternately stacked structure comprised of amorphous PS and smectic-A POTI microdomains whose stacking direction is parallel to the film plane. On heating, the films underwent a phase transformation to a hexagonal cylinder structure with cylindrical POTI domains in the PS matrix oriented normal to the film plane. This phase conversion is induced by the transformation of the POTI domains fro...

Order−Order and Order−Disorder Transitions in Thin Films of an Amphiphilic Liquid Crystalline Diblock Copolymer

In this study, we quantitatively investigated the temperature-dependent phase transition behaviors of thin films of an interesting amphiphilic diblock copolymer, poly(ethylene oxide)-b-poly(11-[4-(4-butylphenylazo)phenoxy]undecyl methacrylate) (p(EO)-b-p(MAAZ)) and the resulting morphological structures by using synchrotron grazing incidence X-ray scattering (GIXS) and differential scanning calorimetry. The quantitative GIXS analysis showed that the diblock copolymer in the homogeneous, isotropic melt state undergoes phase-separation near 190 degrees C and then forms a body-centered cubic (BCC) structure of spherical p(EO) domains in the p(MAAZ) matrix, at which point the p(EO) domains and the p(MAAZ) matrix are both in amorphous, liquid states. The BCC structure of spherical p(EO) domains is converted to a hexagonal cylinder structure near 120 degrees C, which is induced by the transformation of the isotropic phase of the p(MAAZ) matrix to the smectic A phase, which is composed of a laterally ordered structure of p(MAAZ) blocks with fully extended side groups. The resulting hexagonal cylinder structure is very stable below 120 degrees C. This microscopic hexagonal cylinder structure is retained as the smectic A phase of the p(MAAZ) matrix undergoes further transitions to smectic C near 104 degrees C and to a smectic X phase near 76 degrees C, while the amorphous, liquid phase of the p(EO) cylinders undergoes crystallization near -15 degrees C. These complicated temperature-dependent disorder-order and order-order phase transitions in the films were found to take place reversibly during the heating run. A face-centered orthorhombic structure of p(EO) domains was also found during the heating run and is an intermediate structure in the hexagonal cylinder structure to BCC structure transformation. We use these structural analysis results to propose molecular structure models at various temperatures for thin films of the diblock polymer.

Influence of Electric Field on the Phase Transitions of the Hexagonal Cylinder Phase of Diblock Copolymers

We have used the cell dynamic simulations (CDS) method to study the evolution of asymmetric and symmetric diblock copolymers under electric fields. For symmetric diblock copolymers, long-range-ordered lamellar phases form readily under electric fields. For asymmetric diblock copolymers, sphere-to-cylinder phase transitions occur rapidly when strong electric fields are applied, but it takes longer for the system to form hexagonal cylinder structures. The results of these simulations suggest that the sphere phase is stable under weak electric fields, but a threshold electric intensity exists for the sphere-to-cylinder phase transition. In addition, we also studied the kinetic pathways of the transition of the lamellar phase to the hexagonal cylinder phase of the asymmetric diblock copolymers under electric fields. Hexagonal cylinder structures form when the lamellar phase is subjected to a sudden temperature jump. The scattering functions suggest that the hexagonal cylinder structures are very regular and possess very few flaws.

Synthesis and Structural Characterization of Hollow Hexagonal Cylinder Co–SiO2 Composites Prepared in a Micelle Solution

Abstract Novel submicron scale composites with hollow hexagonal cylinder structures were prepared by hydrolysis of tetraethyl orthosilicate in a micelle solution composed of polyoxyethylene (n = 15) cetyl ether/cyclohexane/water containing Co–N2H4 compound nanoparticles.

Nanoorganization and Phase Behavior of Mixtures of Nicotinic Acid with Dodecylbenzenesulfonic Acid

Mesomorphically ordered structures and phase behavior of the mixtures of nicotinic acid (NICA) and dodecylbenzenesulfonic acid (DBSA) were investigated by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and polarized optical microscopy (POM). The POM observations revealed that the NICA–DBSA mixtures spontaneously formed liquid crystalline phases, although both NICA and DBSA were not liquid crystalline molecules. The NICA–DBSA mixtures formed ordered lamellar structures in DBSA‐rich mixtures and hexagonal cylinder structure in NICA‐rich mixtures. The mesomorphically ordered structures and optical anisotropy were caused by hierarchical interactions in the NICA–DBSA mixtures. The phase diagram divided into five regions—optically isotropic disordered phase, optically isotropic lamellar phase, optically anisotropic lamellar phase, optically anisotropic cylinder phase, and crystalline solid phase—is drawn by summarizing the XRD and POM results.