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Find video protocols related to scientific articles indexed in Pubmed.
Hierarchical superstructures from a star-shaped molecule consisting of a cyclic oligosiloxane with cyanobiphenyl moieties.
Soft Matter
PUBLISHED: 11-20-2014
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Unconventional star-shaped liquid crystals (abbreviated as SiLCs) were successfully synthesized by chemically connecting four cyanobiphenyl anisotropic mesogens to the periphery of a super-hydrophobic and ultra-flexible cyclic tetramethyltetrasiloxane ring with flexible hexyl chains. Based on the combined experimental techniques of differential scanning calorimetry (DSC), cross-polarized optical microscopy (POM), solid-state carbon-13 ((13)C) nuclear magnetic resonance (NMR) spectroscopy and one-dimensional (1D) wide-angle X-ray diffraction (WAXD), it was found that the SiLC molecule exhibited the monotropic phase transition from a LC phase to a crystalline phase. The crystalline phase was only detected during slow heating processes above its glass transition temperature, while a LC phase was formed both during cooling and during heating processes. The hierarchical superstructures were identified from the structure-sensitive 2D WAXD of the macroscopically oriented SiLC film and confirmed by selected area electron diffraction (SAED) of the SiLC single crystals. The molecular packing symmetry in the monoclinic unit cell was further investigated by computer simulations on the real and reciprocal spaces. Macroscopically oriented SiLC hierarchical superstructures on the different length scales may provide the targeted physical properties, which can allow us to apply SiLC molecules in the fields of electro-optical devices and nonlinear optics.
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Thermal- and photo-induced phase-transition behaviors of a tapered dendritic liquid crystal with photochromic azobenzene mesogens and a bicyclic chiral center.
Chemistry
PUBLISHED: 02-10-2014
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A ribbon-shaped chiral liquid crystalline (LC) dendrimer with photochromic azobenzene mesogens and an isosorbide chiral center (abbreviated as AZ3 DLC) was successfully synthesized and its major phase transitions were studied by using differential scanning calorimetry (DSC) and linear polarized optical microscopy (POM). Its ordered structures at different temperatures were further identified through structure-sensitive diffraction techniques. Based on the experimental results, it was found that the AZ3 DLC molecule exhibited the low-ordered chiral smectic (Sm*) LC phase with 6.31?nm periodicity at a high-temperature phase region. AZ3 DLC showed the reversible photoisomerization in both organic solvents and nematic (N) LC media. As a chiral-inducing agent, it exhibited a good solubility, a high helical-twisting power, and a large change in the helical-twisting power due to its photochemical isomerization in the commercially available N LC hosts. Therefore, we were able to reversibly "remote-control" the colors in the whole visible region by finely tuning the helical pitch of the spontaneously formed helical superstructures.
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From random coil polymers to helical structures induced by carbon nanotubes and supramolecular interactions.
Macromol Rapid Commun
PUBLISHED: 07-11-2013
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A simple method is reported for the preparation of double-helical structures through a series of achiral random and block copolymers poly(styrene-co-4-vinylbenzyl triazolylmethyl methylthymine) (PS-co-PVBT) with various T units on the side chains through click reactions of poly(styrene-co-4-vinylbenzyl azide) (PS-co-PVBN(3)) with propargyl thymine (PT) and also the synthesis of the A-appended pyrene derivative (A-Py) through click chemistry. This double-helical structure is observed from achiral random-coil polystyrene (PS) main chains, stabilized through the combination of multiple A-T hydrogen bonds, and ?-? stacking between pyrene units and single-walled carbon nanotubes (SWCNTs).
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Tunable mesoporous lamellar silicas prepared using poly(ethylene oxide-b-L-lactide) and poly(ethylene-b-ethylene oxide-b-L-lactide) block copolymers as templates.
J Nanosci Nanotechnol
PUBLISHED: 06-15-2013
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In this study, we synthesized poly(ethylene oxide-b-L-lactide) (PEO-PLLA) diblock copolymers and poly(ethylene-b-ethylene oxide-b-L-lactide) (PE-PEO-PLLA) triblock terpolymers as templates for the preparation of mesoporous lamellar silicas, possessing single, bimodal, or trimodal pore size distributions, through an evaporation-induced self-assembly (EISA) approach. As templates, we synthesized the diblock copolymers EO114LLA26 and EO114LLA130 and the triblock terpolymers E13EO42LLA26 and E13EO42LLA35 using simple ring-opening polymerization. Small-angle X-ray scattering, transmission electron microscopy, and N2 sorption measurements revealed that the mesoporous silicas displayed the morphologies of either lamellar silica walls featuring a distribution of many short cylindrical mesopores or pure lamellar structures. The morphology was greatly affected by the nature of the template (diblock or triblock copolymer) and the molecular weight of the PLLA segment in the block copolymer.
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On modulating the self-assembly behaviors of poly(styrene-b-4-vinylpyridine)/octyl gallate blends in solution state via hydrogen bonding from different common solvents.
Langmuir
PUBLISHED: 07-12-2011
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We have investigated the complexation-induced phase behavior of the mixtures of poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) and octyl gallate (OG) due to hydrogen bonding in different solvents. The Fourier transform infrared spectroscopic result indicates that the hydrogen-bonding was formed between the P4VP blocks and OG in both THF and DMF, implying the P4VP blocks can bind to OG. For PS-b-P4VP/OG mixture in chloroform, the morphological transitions were induced from the unimer configuration to swollen aggregate and complex-micelles by adding OG. Interestingly, the complex-micelles can lead the formation of the honeycomb structure from chloroform solution. The PS-b-P4VP/OG mixture in THF, behaving an amphiphilic diblock copolymer in solution state, exhibited a series of morphological transitions from sphere, pearl-necklace-liked rod, worm-liked rod, vesicle, to core-shell-corona aggregates by increasing the OG content. In contrast, the PS-b-P4VP/OG mixture in DMF maintained the unimer configuration upon adding OG. Therefore, the complexation-induced morphology of the mixtures of PS-b-P4VP and OG can be mediated by adopting different common solvents to affect the self-assembly behavior.
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Glial cell line-derived neurotrophic factor gene transfer exerts protective effect on axons in sciatic nerve following constriction-induced peripheral nerve injury.
Hum. Gene Ther.
PUBLISHED: 05-23-2011
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Damage to peripheral nerves following trauma or neurodegenerative diseases often results in various sensory and motor abnormalities and chronic neuropathic pain. The loss of neurotrophic factor support has been proposed to contribute to the development of peripheral neuropathy. The main objective of this study was to investigate the protective effect of glial cell line-derived neurotrophic factor (GDNF) using peripheral gene delivery in a rat model of constriction-induced peripheral nerve injury. In this study, it was shown that mechanical and thermal hypersensitivity increased on the injured limb at day 7 after chronic constrictive injury (CCI) was induced. The neurological changes were correlated with the structural changes and loss of GDNF/Akt signaling, particularly in the distal stump of the injured sciatic nerve. Subsequently, recombinant adenovirus was employed to evaluate the potential of intramuscular GDNF gene delivery to alleviate the CCI-induced nerve degeneration ad neuropathic pain. After CCI for 3 days, intramuscular injection of adenovirus encoding GDNF (Ad-GDNF) restored the protein level and activity of GDNF/Akt signaling pathway in the sciatic nerve. This was associated with an improved myelination profile and behavioral outcomes in animals with CCI. In conclusion, the present study demonstrates the involvement of GDNF loss in the pathogenesis of CCI-induced neuropathic pain and the therapeutic potential of intramuscular GDNF gene delivery for the treatment of peripheral nerve degeneration.
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Using colloid lithography to fabricate silicon nanopillar arrays on silicon substrates.
J Colloid Interface Sci
PUBLISHED: 02-15-2011
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In this study, we partially grafted geminal silanol groups in the protecting organic shells on the surfaces of gold nanoparticles (AuNPs) and then assembled the alkyl-AuNP-Si(OH)(4) particles onto the surfaces of silicon (Si) wafers. The density of assembled AuNPs on the Si surface was adjusted by varying the geminal silanol group content on the AuNP surface; at its optimal content, it approached the high assembly density (0.0254 particles/nm(2)) of an AuNP assembled monolayer. Using reactive-ion etching (RIE) with the templates as masks, we transferred the patterned AuNP assemblies to form large-area, size-tunable, Si nanopillar arrays, the assembly density of which was controlled by the dimensions of the AuNPs. Using this colloidal lithography (CL) process, we could generate Si nanopillars having sub-10-nm diameters and high aspect ratios. The water contact angles of the high-aspect-ratio Si nanopillars approached 150°. We used another fabrication process, involving electron beam lithography and oxygen plasma treatment, to generate hydrophilic 200-nm-resolution line patterns on a Si surface to assemble the AuNPs into 200-nm-resolution dense lines for use as an etching mask. Subsequent CL provided a patterned Si nanopillar array having a feature size of 200 nm on the Si surface. Using this approach, it was possible to pattern sub-10-nm Si nanopillar arrays having densities as high as 0.0232 nm(-2).
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Self-assembly behavior and photoluminescence property of bispyrenyl-POSS nanoparticle hybrid.
J Colloid Interface Sci
PUBLISHED: 02-14-2011
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Two flexible ether bonds were designed to connect two pyrene rings on a polyhedral oligomeric silsesquioxane (BPy-POSS) to enrich the fraction of "intrinsic intramolecular pyrene-dimer" on the surface of crystal isobutyl-POSS (iBu-POSS) thin-films. Compared to the monomer emission of 1-pyrenemethanol (Py-OH), the emission spectra of BPy-POSS in dichloromethane show the large proportion of intramolecular and intermolecular excimers due to the formation of pyrenyl dimers or aggregates via the easy rotation of two adjacent ether bonds and the ?-? interaction of pyrene rings, respectively. By blending inert iBu-POSS, the fluorescent dimers or aggregates of 5 wt.% and 20 wt.% BPy-POSS are distributed on the surface of iBu-POSS crystal fractal pattern as shown by confocal photoluminescence microscopy. Upon exposure to the vapors of nitrobenzene, the 5 wt.% BPy-POSS blend shows the similar quenching efficiency as 100 wt.% BPy-POSS blends, indicating the better excimer dispersion for vapor permeability of blend thin-films.
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Improved reliability from a plasma-assisted metal-insulator-metal capacitor comprising a high-k HfO2 film on a flexible polyimide substrate.
Phys Chem Chem Phys
PUBLISHED: 01-26-2010
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We have used a sol-gel spin-coating process to fabricate a new metal-insulator-metal (MIM) capacitor comprising a 10 nm-thick high-k thin dielectric HfO(2) film on a flexible polyimide (PI) substrate. The surface morphology of this HfO(2) film was investigated using atomic force microscopy and scanning electron microscopy, which confirmed that continuous and crack-free film growth had occurred on the film surface. After oxygen (O(2)) plasma pretreatment and subsequent annealing at 250 degrees C, the film on the PI substrate exhibited a low leakage current density of 3.64 x 10(-9) A cm(-2) at 5 V and a maximum capacitance density of 10.35 fF microm(-2) at 1 MHz. The as-deposited sol-gel film was completely oxidized when employing O(2) plasma at a relatively low temperature (ca. 250 degrees C), thereby enhancing the electrical performance. We employed X-ray photoelectron spectroscopy (XPS) at both high and low resolution to examine the chemical composition of the film subjected to various treatment conditions. The shift of the XPS peaks towards higher binding energy, revealed that O(2) plasma treatment was the most effective process for the complete oxidation of hafnium atoms at low temperature. A study of the insulator properties indicated the excellent bendability of our MIM capacitor; the flexible PI substrate could be bent up to 10(5) times and folded to near 360 degrees without any deterioration in its electrical performance.
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Resonance effect on self- and inter-association hydrogen bonding interaction of polymer blend.
J Phys Chem B
PUBLISHED: 01-09-2010
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A comparative study of three poly(methacrylamides) containing different N-substitutions was carried out in order to obtain a better understanding of the resonance effects on the inter-association and self-association hydrogen bonding interactions in polymer blends. DSC and solid-state NMR analyses are employed to study the relative miscibility of these three binary blends, indicating that the PNPAA/P4VP blend has a better miscibility than the PNMAA/P4VP and PNCHAA/P4VP blends, because the resonance characteristic of the aromatic ring in PNPAA enhances the inter-association hydrogen bonding with P4VP based on FTIR and solid-state NMR analyses.
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Columnar structures from asymmetrically tapered biphenylamide.
J Phys Chem B
PUBLISHED: 09-22-2009
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An asymmetrically tapered N,N-tris[[(2-dodecylaminocarbonyl)ethyl]methyl]-4-biphenylamide (asym-C(12)PhA, where n is the number of carbon atoms in the alkyl chains, n = 12) was newly designed and synthesized. In this asymmetrically tapered asym-C(12)PhA biphenylamide, H-bondable hydrophilic amide moieties are located at between a rigid hydrophobic biphenyl rod and three flexible hydrophobic alkyl chains. Computer energy minimization indicated that three-dimensional (3D) geometry of asym-C(12)PhA biphenylamide looks like a cone with dimensions of 3.01 nm in height and 1.44 nm in bottom radius. Phase transitions and supra-molecular structures were identified utilizing the combined techniques of differential scanning calorimetry, 1D wide-angle X-ray diffraction (1D WAXD), Fourier-transform infrared spectroscopy, and solid-state (13)C nuclear magnetic resonance analyses. The asym-C(12)PhA self-assembled into a highly ordered columnar mesophase just below the isotropization temperature and then transformed to 3D columnar crystalline phase (Phi(Cr)) on further cooling. Selected area electron diffractions in transmission electron microscopy (TEM) along with 1D WAXD and cross-polarized optical microscopy suggested that discotic building blocks were constructed by rotating 120 degrees of three asym-C(12)PhA with respect to neighboring ones and the tmb (top-middle-bottom) stacked discotic building blocks further self-organized into columns. These columns are laterally intercalated to form the Phi(Cr) phase. On the basis of the TEM image and polyethylene surface decoration technology, it was identified that the self-assembled asym-C(12)PhA fibers with approximately 1 mum in diameter and several millimeters in length were braids of tiny single crystals.
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The Self-Assembled Structure of the Diblock Copolymer PCL-b-P4VP Transforms Upon Competitive Interactions with Octaphenol Polyhedral Oligomeric Silsesquioxane.
Macromol Rapid Commun
PUBLISHED: 06-22-2009
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This paper describes the miscibility and self-assembly, mediated by hydrogen-bonding interactions, of new block copolymer/nanoparticle blends. The morphologies adopted by the immiscible poly[(?-caprolactone)-block-(4-vinyl pyridine)] (PCL-b-P4VP) diblock copolymer changes upon increasing the number of competitive hydrogen-bonding interactions after adding increasing amounts of octaphenol polyhedral oligomeric silsesquioxane (OP-POSS). Transmission electron microscopy reveals morphologies that exhibit high degrees of long-range order, such as cylindrical and spherical structures, at relatively low OP-POSS contents, and short-range order or disordered structures at higher OP-POSS contents. Analyses performed using differential scanning calorimetry, wide-angle X-ray diffraction, and FT-IR spectroscopy provide positive evidence that the pyridyl units of the P4VP block are significantly stronger hydrogen-bond acceptors toward the OH group of OP-POSS than are the C?O groups of the PCL block, thereby resulting in excluded and confined PCL phases.
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Upregulation of hepatoma-derived growth factor is involved in murine hepatic fibrogenesis.
J. Hepatol.
PUBLISHED: 04-29-2009
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Hepatoma-derived growth factor (HDGF) expression is correlated with progression of hepatocellular carcinoma. Since liver fibrosis frequently occurs before hepatoma development, this study investigated the expression profile of HDGF and its relationship with transforming growth factor-beta (TGF-beta) signaling in experimental models of hepatofibrogenesis.
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Phase behaviors and structures of a symmetrically tapered biphenylamide.
J Phys Chem B
PUBLISHED: 04-03-2009
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A symmetrically tapered N,N-bis[tris[(2-dodecylaminocarbonyl)ethyl]methyl]]-4,4-biphenylamide (d-C(n)PhA, where n is the number of carbon atoms in the alkyl chains, n = 12), was newly designed and synthesized in order to investigate the supramolecular ordered structures induced by phase separation, hydrogen (H)-bonding, and pi-pi stacking interaction. This symmetrically tapered d-C(12)PhA biphenylamide consists of three different parts: H-bondable hydrophilic amide moieties, a rigid hydrophobic biphenyl aromatic core, and three flexible hydrophobic alkyl chains at each end of the core. Major phase transitions and supramolecular structures in d-C(12)PhA biphenylamide were characterized by differential scanning calorimetry (DSC), one-dimensional (1D) wide-angle X-ray diffraction (WAXD), 1D and 2D Fourier-transform infrared spectroscopy (FT-IR), and solid-state (13)C nuclear magnetic resonance (NMR). The symmetrically tapered d-C(12)PhA biphenylamide formed a hexagonal columnar (Phi(H)) liquid crystalline (LC) mesophase at a cooling process and a highly ordered columnar (Phi(HK)) crystalline phase at a subsequent heating process. Selected area electron diffractions (SAED) from single crystals combined with the results of WAXD and POM suggest that discotic building blocks are constructed by three d-C(12)PhA biphenylamides rotating 60 degrees with respect to neighboring ones and the ABC stacked discotic building blocks further self-assemble into columns and then these columns are laterally close-packed to give nanorods. Furthermore, it was identified that the long axis of column is parallel to the long axis of rods.
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Complexation of fluorescent tetraphenylthiophene-derived ammonium chloride to poly(N-isopropylacrylamide) with sulfonate terminal: aggregation-induced emission, critical micelle concentration, and lower critical solution temperature.
Langmuir
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Amphiphilic polymers with hydrophilic poly(N-isopropylacylamide) (PNIPAM) shell connecting hydrophobic tetraphenylthiophene (TP) core, which has the novel aggregation-induced emission (AIE) property, by ionic bonds were prepared to explore the AIE-operative emission responses toward critical micelle concentration (CMC) and lower critical solution temperature (LCST). To exercise the idea, ammonium-functionalized TP2NH(3)(+) and sulfonate-terminated PNIPAM were separately prepared and mixed in different molar ratios to yield three amphiphilic TP-PNIPAMn complexes for the evaluations of CMC and LCST by fluorescence responses. The nonemissive dilute aqueous solutions of TP-PNIPAMn became fluorescent when increasing concentrations above CMC. Heating micelles solution to temperatures above LCSTs causes further enhancement on the emission intensity. The fluorescence responses are explained by the extent of aggregation in the micelles and in the globules formed at room temperature and at high temperatures, respectively.
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Hierarchical mesoporous silica fabricated from an ABC triblock terpolymer as a single template.
Macromol Rapid Commun
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Hierarchical mesoporous silicas containing two kinds of mesoporous size are successfully synthesized using the simple evaporation-induced self-assembly (EISA) strategy. Two blocks of hydrophobic segments (PE and PCL) in the poly(ethylene-block-ethylene oxide-block-?-caprolactone) (PE-PEO-PCL) triblock copolymer are involved in the two types of mesopore after calcination, the PE segment being attributed to the face-centered cubic (fcc) morphology (spherical pores) and the PCL segment attributed to the tetragonal cylinder structure (cylindrical pores).
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