Materials Literature
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The synthesis and characterization of a new series of mesogen-jacketed liquid crystal polymers, poly{2,5-bis[(para-substituted phenyl)oxycarbonyl]styrene}s, based on 2-vinylterephthalic acid are reported. These polymers formed very stable liquid crystal phases above the glass transition temperatures. A brief compariso…
Magnon linewidth of La_1.2 Sr_1.8 Mn_2 O_7 near the Brillouin zone boundary is investigated from both theoretical and experimental points of view. Abrupt magnon broadening is ascribed to a strong magnon-phonon coupling. Magnon broadening observed in cubic perovskite manganites is also discussed.
Hexagonal BaTiO_3 undergoes a structural phase transition to an orthorhombic C222_1 phase at T_0 = 222 K. The transition is driven by a soft optical mode with E_2u symmetry whose couplings force the appearance of a spontaneous E_2g strain (improper ferroelastic character). Staying within the same E_2u subspace, the sy…
We reexamine two essential issues within the Peierls-Nabarro model which are critical in obtaining accurate values for the Peierls stress. The first issue is related to the sampling scheme of the misfit energy across the glide plane and the second one is the effect of relaxation on the Peierls stress. It is shown that…
New approach on interpretation and processing of Raman spectra of complex perovskites is suggested. Raman spectra of $PbMg_{1/3}Nb_{2/3}O_{3}$ and $% PbSc_{1/2}Ta_{1/2}O_{3}$ are successfully described on the basis of the phonon-confinement model and validity of the method is demonstrated on good agreement of experime…
The linear generalized equation described in this paper provides a further dimension to the prediction of lattice potential energies/enthalpies of ionic solids. First, it offers an alternative (and often more direct) approach to the well-established Kapustinskii equation (whose capabilities have also recently been ext…
Kinetics and dynamics of CO oxidation have been studied on a stepped Pd(335) surface at a steady-state condition and compared with those on flat Pd(111). The infrared (IR) chemiluminescence technique was applied to determine where the active catalytic sites are on the Pd(335) surface. Since the vibrational energy stat…
We present a series of new 6,6‘-distyryl-3,3‘-bipyridine derivatives synthesized via a Knoevenagel condensation reaction and disubstituted with electron donor and acceptor groups. These molecules were characterized by spectroscopic methods (NMR, Raman, UV−vis, photoluminescence). These compounds were all found to exhi…
ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorDendrimers with Both Hydrophilic and Hydrophobic Chains at Every EndYijun Pan and Warren T. FordView Author Information Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078 Cite this: Macromolecules 1999, 32, 1…
A promising route to new functionalized compounds could be provided by two new heteropolyoxothio anions resulting from self−condensation of the [Mo2S2O2]2+ building unit with arsenate or phosphate ions. There is 31P NMR evidence (illustrated) that the three peripheral PO4 or AsO4 groups in the products are labile.
The microphase separation of symmetric cyclic diblock copolymer with decreasing temperature is simulated using the Monte Carlo method. In order to investigate the effect of the ring-shape chain architecture on order–disorder transition (ODT), the microphase separation of the cyclic diblock copolymer is compared with t…
The preparation, rheological behavior, and solution properties of branched poly(3-hydroxy butyrate)- co -(3-hydroxy valerate), PHBV, are described. Branching is produced by the use of dicumyl peroxide (DCP) during the reactive extrusion of PHBV. The shear viscosities of reactively extruded PHBV and the straight-chain…
We report on the structure and dynamics of model mono-, di-, and tri-ω-functionalized three-arm star polybutadiene melts. By using x-ray scattering and dynamic rheological measurements, we find that functionalization of the arm ends can lead to distinctly different supramolecular structures and material behavior. The…
We study the nematic–isotropic transition in model colloidal systems composed of platelets of various shapes using grand canonical simulations. This is of relevance for recently synthesized hard platelet systems, since the platelets in such systems are found to be not circular but irregular hexagons, and so cannot be…
The nanoenvironment provided by the neighboring dendra characteristically influences the redox potentials and the photophysical properties of the tetraphenylporphyrin–zinc (Zn-TPP; denoted as P in Figure) chromophore within the dendrimers 1, which are based on C60 as a structure-determining core. Such functional dendr…
Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry was utilized to study simple poly(ethylene glycol)s (PEG) and a series of amphiphilic copolymers prepared from PEG and dendritic molecules. For the amphiphilic copolymers with branched dendritic structures, MALDI-TOF spectrometry…
Despite the relevance to most aspects of crystallization, a comprehensive understanding of the kinetics of heterogeneous nucleation has not been well established yet. In this paper, a new kinetic model based on the “steady-state” approach will be put forward to describe both heterogeneous and homogeneous nucleation. A…
A method, using a Corbino disk sample geometry, is described and applied to study of resistive tails of sintered $YBCO$. When the transport current passes radially from the rim of the disk sample to its center, the two component potential drop signal is detected below $T_c$, which is due to (i) quasiparticles $W_q$ an…
We measured the temperature dependence of the linear high field Hall resistivity of La_0.67Ca_0.33MnO_3 (T_C=232K) and La_0.67Sr_0.33MnO_3 (T_C=345K) thin films in the temperature range from 4K up to 360K in magnetic fields up to 20T. At low temperatures we find a charge carrier density of 1.3 and 1.4 holes per unit c…
Orange− or yellow−orange-colored aqueous dispersions of ultrafine gold particles (∼2 nm) result from the γ-irradiation of deaerated solutions containing hydrolyzed AuCl 4 - and poly(vinyl alcohol) or poly(vinylpyrrolidone), respectively. The particles have a weak and very broad plasmon absorption band with maximum in…