Highly Ordered Hexagonal Arrays of Hybridized Micelles from Bimodal Self‐Assemblies of Diblock Copolymer Micelles

We demonstrate the formation of highly ordered hexagonal arrays of hybridized polystyrene–poly(4‐vinyl pyridine), PS–PVP, micelles with controllable size by solvent annealing techniques. Because the formation of hybridized micelles was prohibited in the mixture solutions of two different‐sized PS–PVP micelles, single‐layered films with bimodal self‐assemblies of small and large micelles were fabricated from the mixture solutions by adjusting their mixing ratios. When the single‐layered films were solvent annealed by saturated vapor of tetrahydrofuran (THF), on the other hand, small and large PS–PVP micelles in the bimodal self‐assemblies merged together to form hybridized micelles. In addition, the hybridized micelles arranged themselves in a highly ordered hexagonal array, the diameter and center‐to‐center distance of which were precisely adjusted by varying the mixing ratio of small to large micelles in the bimodal assemblies.

     

Localized synthesis of polypyrrole in the nanopattern of monolayer films of diblock copolymer micelles

A single-layered array of polystyrene-block-poly(4-vinylpyridine), PS-PVP, micelles in hexagonal order, fabricated by spin coating, was employed as a nanostructured template for synthesis of polypyrrole, a conducting polymer, in nanometer-sized domains. Oxidative catalysts of FeCl3 for the polymerization were selectively loaded in spherical PVP nanodamains so that they were hexagonally arranged over the film but confined in the nanometer range. The vapor-phase polymerization of pyrrole was localized in the PVP nanodomains, leading to a morphological transition from spherical to wormlike domains. In addition, the nanodomains containing polypyrrole were converted to open cavities by ethanol, a PVP block-selective solvent.     

Co-deposits of Pt and Bi on Au disk toward formic acid oxidation

Journal of Solid State Electrochemistry - Presented in this work is an investigation of co-deposits of Pt and Bi on Au disk (Pt-Bi/Au) toward formic acid oxidation (FAO) using voltammetry and X-ray...     

TWO FEEDBACK PROBLEMS FOR GRAPHS WITH BOUNDED TREE-WIDTH

Many difficult (often NP-complete) optimization problems can be solved efficiently on graphs of small tree-width with a given tree decomposition. In this paper,it is discussed how to solve the minimum feedback vertex set problem and the minimum vertex feedback edge set problem efficiently by using dynamic programming on a tree-decomposition.     

Biocompatibility of a PDMS-coated micro-device: Bladder volume monitoring sensor

We evaluated the biocompatibility of a dimethylpolysiloxane-coated micro-device which had been designed for monitoring real-time bladder volume in previous studies.The extract assay with dimethylpolysiloxane which had been used for coating the micro-device to measure the bladder volume was performed as an in vitro cytotoxicity test.For in vivo biocompatibility testing,the inflammatory responses around the implantation site of the micro-device in subcutaneous tissue of rat were assessed by light microscope with H&E stain and fluorescence microscope with ED1 stain and von Willebrand factor stain.The averages of cell viability in dimethylpolysiloxane group were 84.6%and 82.3%at 24 h and 72 h incubation, respectively.The qualitative evaluations with light and fluorescence microscope revealed that the inflammatory changes peaked during 2 weeks but almost disappeared at 4 weeks after implantation of devices.The quantitative evaluations for granulation layer formation and neovascularization showed that the thickness of the layer in dimethylpolysiloxane group peaked during 2 weeks but it came to be stabilized at 4 weeks as thin as at 2 weeks in control group,and the frequency of neovascularization was higher in dimethylpolysiloxane group than in control group but it was not increased with time.The dimethylpolysiloxane-coated micro-device is thought be a reliable bio-medical device.     

PVDF-HFP/PMMA-coated PE separator for lithium ion battery

Microporous poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP)/poly(methyl methacryate) (PMMA)-coated polyethylene (PE) separators were prepared by a simple dip-coating process with various compositions of PVDF-HFP/PMMA mixture under 40% relative humidity condition. The results indicate that the porosity, liquid electrolyte uptake, and ionic conductivity of the coated separators are largely affected by a ratio of PVDF-HFP/PMMA mixture and the highest porosity, electrolyte uptake, and ionic conductivity can be achieved at a composition of PVDF-HFP/PMMA (5/5). The results of the cell performance tests also reveal that the PE separator coated with PVDF-HFP/PMMA in a ratio of 5:5 provides better rate capability and cycle stability than other PE separators coated with different ratios.     

A module of a TiO2 nanocrystalline dye-sensitized solar cell with effective dimensions

As dye-sensitized solar cells (DSSCs) have advanced to large-scale applications from lab-level research, the large-scale performance has attracted much attention. Modules of DSSCs with size up to 10 cm × 15 cm have been investigated to optimize the efficiency for effective application. Essentially, these modules have an extended structure with lab-scale works with the exception of the dimensions and methods for the series connection. The 10 cm × 10 cm modules have shown an efficiency of 6.3% without a scattering layer and over 6.6% with a scattering layer. While the fill factors of modules depend on the width of each TiO₂ unit cell, they are much less dependent on the lengths of the unit cells.     

Cylindrical cavity with a circumferential edge crack subjected to a uniform shearing stress

This paper contains an analysis of the stress distribution in an elastic medium having cylindrical cavity with a circumferential edge crack when it is deformed by the application of uniform shearing stress. By making a suitable representation of the stress function for the problem, the problem is reduced to the solution of a pair of singular integral equations. This pair of singular integral equations is solved numerically, and the stress intensity factor due to the effect of the crack size is calculated. Also the crack opening displacements are displayed in graphical forms.Received: January 24, 2002; revised: October 17, 2002     

Epitaxial MnP thin films: epitaxial growth,magnetic and electrical properties

We have grown 500 Å MnP on undoped GaAs(1 0 0) substrate using solid-source molecular beam epitaxy. In order to characterize the crystal structure of MnP, we performed in-situ reflection high energy electron diffraction and θ–2θ XRD X-ray diffraction studies. From the measurements of superconducting quantum interference device, Quantum Design, MnP thin film shows ferromagnetic ordering at around 291.5 K. It shows a metallic resistivity in MnP thin film.     

Probe diffusion from dilute to concentrated in polyelectrolyte solution: salt effect

The adsorption behaviors between a positively charged poly(allyamine) hydrochloride (PAH) matrix and negatively charged sulfate polystyrene (PS) particle probe were investigated using dynamic light scattering (DLS) and fluorescence photobleaching recovery (FPR) with reference to the matrix and salt concentration. The system experienced a steep decrease of diffusion (flocculation) under dilute conditions and a gradual decrease above semidilute concentrations. The fluorescence photobleaching recovery and viscometry experiments revealed that the probe behaviors in the polyelectrolyte solution were strongly affected by the coil overlap concentration (0.5 g/L poly(allyamine) hydrochloride). Near the coil overlap concentration, the hydrodynamic radius representing the entanglement dimension of the matrix was approximately 30 nm; however, at higher concentrations the radius gradually decreased, suggesting a transition toward a network structure. In this system, the salt performed two roles: (1) reinforcing the electrostatic interaction, and (2) preventing electrostatic interaction between the probe and the matrix.