Materials Literature
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Abstract A novel preparation approach for high‐performance polyimide gels that are swollen or have a jungle‐gym‐type structure is proposed. A new rigid and symmetric trifunctional amine, 1,3,5‐tris(4‐aminophenyl)benzene (TAPB), was synthesized as a crosslinker. Three different kinds of amic acid oligomers derived from…
Thermally activated mobility of clusters of interstitial atoms is an important factor driving microstructural evolution of materials under irradiation. Molecular dynamics simulations show that the statistics of one-dimensional Brownian motion of clusters is characterized by unusual correlated jumps spanning many inter…
Mixtures of Ln(SC(6)F(5))(3) and Ln(EPh)(3) (E = S, Se) react with elemental E to give chalcogen-rich clusters with fluorinated thiolate ancillary ligands. The structures of both (THF)(6)Yb(4)S(SS)(4)(SC(6)F(5))(2) and (THF)(6)Yb(4)Se(SeSe)(4)(SC(6)F(5))(2) have been established by low-temperature single-crystal X-ray…
New misfit cobaltites, containing lead and mercury, have been synthesized, [Pb 0.7 Sr 1.9 Co 0.4 O 3 ][CoO 2 ] 1.8 and [Pb 0.7 Hg 0.2 Sr 1.9 Co 0.2 O 3 ][CoO 2 ] 1.8 . Their structural study, using high resolution electron microscopy and X-ray powder diffraction, shows that the samples are perfectly homogeneous and co…
The structure and bonding in alpha and beta octamolybdate anions have been investigated using density functional methods. In general, good computational-experimental agreement for the geometrical parameters has been obtained. The electronic structure of the anions has been probed with molecular orbital and Mulliken-Ma…
Rare-earth-doped SiO2 colloids can be grown in a wet chemical procedure by adding the appropriate rare earth chloride to a solution of tetraethoxysilane, glacial acetic acid, and water. The size polydispersity of the particles can be controlled in a seeded growth process, and monodisperse Er3+-doped particles were gro…
Maleated polyethylene/silicate nanocomposite (PEMA/20A) and maleated polyethylene/SiO 2 composite (PEMA/SiO 2 ) were prepared by the melt compounding. Transmission electron microscopy and X-ray scattering results confirmed the exfoliation of the silicate layers (20A) throughout the maleated polyethylene (PEMA) matrix,…
ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTSANS and Cryo-TEM Study of Self-Assembled Diblock Copolypeptide Hydrogels with Rich Nano- through Microscale MorphologyDarrin J. Pochan, Lisa Pakstis, Bulent Ozbas, Andrew P. Nowak, and Timothy J. DemingView Author Information Mater…
Experimental control of block copolymer segregation is ideally achieved by varying temperature, but in practice, the range of segregation is very restricted. A far greater range can be accessed by diluting the block copolymer melt with a solvent, assuming the mixture obeys the so-called dilution approximation. We exam…
UV excitation of ${\mathrm{Ce}}^{3+}$-doped ${\mathrm{Ca}}_{2}{\mathrm{Al}}_{2}{\mathrm{SiO}}_{7}$ melilite crystals produces long-lasting phosphorescence $(1\ensuremath{-}{10}^{3} \mathrm{s})$ from ${\mathrm{Ce}}^{3+}$ ions in addition to the intrinsic ${\mathrm{Ce}}^{3+}$ luminescence with a lifetime of 40 ns. The d…
Polymers containing coumarin and Ru(BpyMe 2 ) 3 2+ chromophores were synthesized using a grafting approach and also a copolymerization approach. It was found that the solubility of polymers made from Ru-containing monomers was higher than that observed for comparable polymers obtained by grafting of Ru complexes onto…
Surface-tethered triblock copolymers composed of poly(methyl acrylate), poly(methyl methacrylate), and poly(2-hydroxyethyl methacrylate) were grown from gold substrates by a series of atom transfer radical polymerizations at ambient temperature. GPC determinations of the molecular weights of desorbed triblock homopoly…
Covalently bonded layered silicates/polyimide (BTDA-ODA) nanocomposites have been synthesized from γ-(aminopropyl)triethoxysilane (APTS) grafted kenyaite and poly(amic acid). The existence of covalent bonds between APTS and silicates and between APTS and the dianhydride end groups of the polymer have been confirmed by…
Two novel B 3 monomers, tri(phthalic anhydride) and tri(phthalic acid methyl ester), were synthesized. Hyperbranched polyimides were prepared by A 2 + B 3 polymerizations of (a) 1,4-phenylenediamine (A 2 ) and tri(phthalic anhydride) (B 3 ) (method A) and (b) 1,4-phenylenediamine (A 2 ) and tri(phthalic acid methyl es…
We have studied the thin film morphologies of polystyrene- b -poly(2-vinylpyridine) diblock copolymers and polystyrene- b -poly(2-vinylpyridine)- b -poly( tert -butyl methacrylate) triblock copolymers after “annealing” in the vapor of different solvents. We find distinct differences in the resulting thin film morpholo…
In this paper we report on the optical spectroscopy and upconversion studies of Ho 3+ -doped nanocrystalline and bulk Y 2 O 3, as a function of holmium concentration (0.1, 0.5, 1, 2, 5, and 10 mol %). Emission in the blue, green, red, and NIR portions of the spectrum is recorded after 457.9-nm excitation. Red (646 nm)…
High-field electron-spin-resonance (ESR) experiments have been carried out in single crystals of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ in the concentration range $0<~x<~0.175.$ Different quasioptical arrangements have been utilized for frequencies $40<~\ensuremath{\nu}<~700…
A new model of crystal growth is presented that describes the phenomena on atomic length and diffusive time scales. The former incorporates elastic and plastic deformation in a natural manner, and the latter enables access to time scales much larger than conventional atomic methods. The model is shown to be consistent…
We describe measurements of the stiffness and Young’s modulus, Y of single crystals of molybdenum-based compounds. Atomic force microscopy is used first to image, and then to perform stiffness measurements on crystals which are growing up out of a substrate. Y is extracted by comparing the measured stiffness with that…
Von schwach blau zu intensiv blaugrün: Diese Veränderung der Emission ist die Folge der Reaktion von [RuCl2(POC4Pyr-P,O)2] mit Kohlenmonoxid. Der Grund ist die Bildung des gezeigten Dicarbonylkomplexes, in dem CO das labile Koordinationszentrum des hemilabilen Liganden POC4Pyr verdrängt hat. Die höhere Flexibilität de…